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OCR 21st Century Science: C5 Chemicals of the natural environment
C5 Module Introduction
Pages 130−131 in the Student Book provide an introduction to this module.
When and how to use these pages
These pages summarise what students should already know from KS3 or from previous GCSE units and provide
an overview of the content that they will learn in this module.
o Use these pages as a revision lesson before you start the first new topic.
o Brainstorm everything that students remember about the different topics using the headings as a starting
point. Compare your list with the points on page 130.
o Use the questions on page 130 as a starting point for class discussions.
o Ask students if they can tell you anything about the topics on the right-hand page.
o Make a note of any unfamiliar / difficult terms and return to these in the relevant lessons.
Suitable answers to the questions on page 130 are:
o Substances burn in air showing it contains oxygen. Air will turn limewater cloudy if bubbled though it
showing that it contains carbon dioxide
o Test its malleability and conduction of electricity.
o Add a little sodium carbonate to water in a test tube, stir and check that all the solid has disappeared
o Igneous rocks are crystalline; sedimentary rocks contain fossils.
You could revisit these pages at the following points:
o before lesson c5_06 on giant covalent structures, pages 144−145
o before lesson c5_10 on electrolysis, pages 152−153
Overview of module
Students begin by learning about the substances found in the air, which are molecular, and hence find out about
covalent bonding and the properties of simple molecular substances.
Next we explore the ionic compounds found in seawater, in particular how the ionic bond forms ionic crystals.
Students then discover methods of testing ionic salts to identify the metals and non-metals present.
Students go on to learn about the giant molecules found in the Earth’s crust, and the extraction of metals from
metal ores by reduction with carbon and by electrolysis. Alongside this, students learn about writing chemical
equations and using relative atomic mass and relative formula mass. Finally they learn about the bonding in
metals and the importance that this has.
Obstacles to learning
Students may need extra guidance with the following terms and concepts:
Molecular bonds
Some students may have difficulty in seeing 3-D diagrams as 2-D projections of the shape of molecules.
Students may have little sense of scale as to what constitutes a high or low melting or boiling point.
Difficulty in visualising the forces within and between molecules may leave students still confused as to why
molecules do not break up at their boiling points.
Ionic compounds
It could confuse students that many compounds are ionic but are not found in seawater, are insoluble in water and
do not have ‘simple’ melting and boiling points (they decompose).
Ion tests
Some students have difficulty in understanding that metal ions give the same results with sodium hydroxide
regardless of what other ions are in solution.
The importance of negative results – e.g. no fizzing means no carbonate – can cause confusion.
Giant molecular structures
It can be difficult for students to visualise the 3D structure of giant molecules from diagrams.
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C5 Module Introduction continued
Reduction of copper oxide
There is a high chance of failure in this practical so students may have difficulty in seeing how the small scale and
unsuccessful reaction is scaled up to produce millions of tons of metal a year.
The term ‘reduction’ has rather obscure origins and can be difficult for students to relate to reactions.
Chemical equations
Some students find chemical equations too abstract. Demonstrating reactions and using models can make the
topic more concrete.
Masses
The terms such as ‘relative atomic mass’ can themselves make this topic seem more difficult than it really is. Try to
build up confidence with numbers by giving lots of simple examples.
Electrolysis
The ionic theory of electrolysis requires visualisation of an abstract concept. This is difficult for many students who
may nevertheless be able to learn the definitions and identify the products in the reactions
Metals
The crystal structure of metals is not obvious and the great diversity in properties of metals can make it difficult to
see that one theory can explain all the variations. Poor diagrams can give a picture of the metallic bond that bears
no relation to the incompressible nature of metals.
Practicals in this module
In this module students will do the following practical work:
o
o
o
o
o
o
o
o
investigating the properties of some simple molecular substances (demonstration)
preparing crystals of ionic compounds
testing metal ions
testing negative ions
reducing copper oxide
measuring the mass of reactants and products
electrolysis of a molten salt (demonstration)
investigating the properties of metals (demonstration)
Key vocabulary covered in this module
dry air molecule covalent bond
quantitative data qualitative data intermolecular intramolecular
hydrosphere salts crystals ionic compounds lattice ionic bond molecular ion
precipitate insoluble ionic equation
effervescence
mineral lithosphere giant covalent structure
ore reduce reduction oxidise oxidation redox reaction
relative atomic mass relative formula mass gram formula mass
electrolysis electrolyte decompose electrode cathode anode
malleability metallic bond
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OCR 21st Century Science: C5 Chemicals of the natural environment
C5 Analysing, evaluating and reviewing
Pages142−143 in the Student Book prepare students for controlled assessment.
When and how to use these pages
This activity provides an opportunity to build and assess the skills that students will use when evaluating an
investigation.
Ask students to:
o read through the context and tasks, listing any terms that they do not understand
o as a whole class or in small groups, discuss the tasks to ensure that all students understand the terminology
used and to clarify what is required
o work individually or in small groups to answer the questions for each task.
If time allows, ask the students to mark one another’s work using the mark scheme provided.
Notes
This activity uses students’ knowledge of analytical tests to evaluate the experimental method presented, which is
an attempt to identify white powders by anion tests.
Answers
Task 1
No. They only carried out the second part of the test, using silver nitrate.
Both substances produced a white precipitate with silver nitrate.
Task 2
They should have added nitric acid to both solutions first.
Test tube and test tube rack, dropper (small quantities should be used and the reactions carried out in test
tubes not beakers), and maybe a delivery tube and limewater to test for carbon dioxide.
Task 3
If one of the powders was a carbonate, its solution would fizz when nitric acid was added. Carbon dioxide gas
would be produced which could be collected and tested with limewater. When the fizzing had stopped the
solution would not form a precipitate when silver nitrate was added.
If the other powder was a chloride it would not fizz with nitric acid. It would form a white precipitate with silver
nitrate.
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C5 Analysing, evaluating and reviewing continued
Mark scheme
For grade E, students should show that they can:
o comment about problems encountered during the experiment
o say how the equipment or methods used prevented collection of all the data needed.
For grades D, C, in addition show that they can:
o suggest some improvements to the apparatus or methods used
o or suggest different ways of collecting data
o or explain how the method used gives enough information to write a conclusion.
For grades B, A, in addition show that they can:
o give a detailed set of improvements to the apparatus or method
o or suggest different ways of collecting data and explain why these are better
o or explain why the method used cannot be improved upon.
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OCR 21st Century Science: C5 Chemicals of the natural environment
C5 Exam-style questions
Pages 160−161 in the Student Book are exam-style questions.
When and how to use these pages
These questions are based on the whole of Module C5 and cover a range of different types of questions that
students will meet in their written exams.
o
o
o
o
The questions could be used as a revision test once you’ve completed the module.
Work through the questions as a class as part of a revision lesson.
Ask students to mark each other’s work, using the mark scheme provided.
As a class, make a list of the questions that most students did not get right. Work through these as a class.
Notes on the worked examples
The first question is concerned with the interplay of data and imagination in formulating explanations; it presents
students with four statements to assess which are a mixture of factual data, explanation and creative thinking.
The second question tests students’ ability to apply the analytical tests covered in the module, and requires an
extended answer. The answer provided is missing some essential details required to identify the ions together and
has some spelling errors and so is awarded only 3 marks. Students should attempt to write an answer worth the full
6 marks.
Question 3 assesses students’ ability to make judgements, while the final question tests Higher tier students’ skills
in writing chemical equations. (Note that students will have a data sheet listing the formulae of ions.)
Assessment Objectives
These exam-style questions cover the Assessment Objectives as described below.
Assessment Objectives
Questions
AO1
Recall, select and communicate their knowledge and
understanding of science
1b, 2e, 3, 4a,
worked example 2, 4
AO2
Apply skills, knowledge and understanding of science in
practical and other contexts
1a, 2a, c, d, 4b,
worked example 1, 2
AO3
Analyse and evaluate evidence, make reasoned judgements
and draw conclusions based on evidence
2b, worked example 3
Answers
These answers are also supplied on the Teacher Pack CD so that students can mark their own or their peer’s work.
Question
number
Answer
Additional notes
Mark
1a
The electrical wiring in homes is made
of copper – Copper is a good conductor
of electricity
Central heating pipes in homes are
made of copper – Copper can be bent
easily
Copper (mixed with other metals) is
used in coins – Copper is not very
reactive
All correct: 2 marks
1 correct: 1 mark
2
b
Positive ions in a giant (metallic)
structure attracted to (a sea of) free
electrons
Electrons move freely conducting
electricity (and heat) / strong force so
metals usually have high melting points
1 mark for copper having a giant (metallic)
structure with strong bonds
1 mark for a property explained correctly
2
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C5 Exam-style questions continued
and are strong
2a
b
c
d
The demand for galvanised steel rose in
2006/7 and fell in 2007/8
because the demand for zinc rose and
fell at these times and half of the zinc
was used for galvanising
Description of shape of graph
The impact on the environment would
have been greatest in 2006/7
because it was during this period that
the demand for zinc was greatest
Or vice versa
Gram atomic mass of Zn = 65 g
Gram formula mass of ZnCO3 = 125 g
1 g of zinc carbonate contains 65/125 =
0.52 g zinc
So, 40 g of zinc carbonate contains 40 ×
0.52 = 20.8 g zinc
2 marks for 20.8g
1 mark if correct method used but final
answer wrong
ZnCO3(s) → ZnO(s) + CO2(g)
1 mark for correct formulae
1 mark for correct state symbols
2
1
Explanation related to zinc
1
1
1
2
e
Zinc oxide is heated with carbon
Zinc is reduced during the reaction
because it loses oxygen
Carbon is oxidised during the reaction
because it gains oxygen
1 mark if three words correct
2
3
Relevant points:
both oxygen and silicon dioxide have
covalent bonding
in covalent bonds atoms share pairs of
electrons
the bond is the attraction of the nuclei
for the shared electrons
oxygen is a simple molecule
covalent bonds are strong
in simple molecules such as O2 there
are only weak forces between molecules
hence the low boiling point/it is a gas
in giant covalent structures there are
covalent bonds joining many atoms
together
in a regular arrangement/lattice
hence a lot of energy is needed to melt
silicon dioxide
Labelled diagrams can be used
For 5–6 marks:
Answer demonstrates knowledge of
covalent bonding and how it relates to the
properties of simple and giant molecular
substances. All information given is
relevant, clear, organised and presented
in a structured and coherent format.
Specialist terms are used appropriately.
Few, if any, errors in grammar,
punctuation and spelling
For 3–4 marks:
States and explains some aspects of
covalent bonding. For the most part the
information given is relevant and
presented in a structured and coherent
format. Specialist terms are used for the
most part appropriately. There may be
occasional errors in grammar, punctuation
and spelling
For 1–2 marks:
States that there is covalent bonding in
both materials but the explanations are
missing or incorrect. Answer may be
simplistic. There may be limited use of
specialist terms. Errors of grammar,
punctuation and spelling may be intrusive
For 0 marks:
Insufficient or irrelevant science. Answer
not worthy of credit
6
4a
A, D
1 mark each
Deduct 1 mark for each incorrect answer
(minimum 0)
2
b
Cathode/negative electrode – lithium
Anode/positive electrode – bromine
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Not bromide
1
1
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OCR 21st Century Science: C5 Chemicals of the natural environment
C5 Module Checklist
Pages 158−159 in the Student Book provide a student-friendly checklist for revision.
When and how to use these pages
This checklist is presented in three columns showing progression, based on the grading criteria. Bold italic means
Higher tier only.
Remind students that they need to be able to use these ideas in various ways, such as:
o interpreting pictures, diagrams and graphs
o applying ideas to new situations
o explaining ethical implications
o suggesting some benefits and risks to society
o drawing conclusions from evidence they have been given.
These pages can be used for individual or class revision using any combination of the suggestions below.
o Ask students to construct a mind map linking the points on this checklist.
o Work through the checklist as a class and note the points that need further class discussion.
o Ask students to tick the boxes on the checklist worksheet (on the Teacher Pack CD) if they feel confident
that they are well prepared for the topics. Students should refer back to the relevant Student Book pages to
revise the points that they feel less confident about.
o Ask students to use the search terms at the foot of the relevant Student Book pages to do further research
on the different points in the checklist.
o Students could work in pairs, and ask each other what points they think they can do, and why they think that
they can do those, and not others.
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C5 Module Checklist continued
Module summary
In the introduction to this module, students were presented with a number of new ideas. Work through the list
below as part of their revision. Ask students to write their own summaries and mind maps, using this list as a
starting point.
Simple molecular substances
o The air consists of a mixture of gases all of which are molecular.
o The atoms in a molecule are joined by covalent bonds. The arrangement of the atoms in a molecule can be
represented by a 3-D model or by 2-D or 3-D diagrams.
o The properties of simple molecular compounds are explained by the weak forces between molecules.
Ionic compounds and ion tests
o The Earth’s hydrosphere consist of water with dissolved salts. Salts are ionic compounds.
o The positively and negatively charged ions in an ionic compound are joined by ionic bonds. This is a strong
bond that holds the ions in a regular lattice arrangement.
o The properties of ionic crystals are determined by the strong ionic bonding.
o The metal ions in ionic compounds can be identified by the colour of the precipitate formed whensodium
hydroxide is added to a solution of the salt.
o There are also chemical tests for the negative ions in compounds.
Giant molecular structures
o The Earth’s lithosphere contains minerals (crystals) composed of elements such as silicon and oxygen
o Diamond and graphite are minerals which are crystalline forms of carbon with giant covalent structures.
o The properties of giant molecular substances depend on the structure of the crystal lattice.
Reduction and oxidation
o Some metals can be extracted from their ores using carbon. This reduces the metal oxide to the metal.
o Reduction is the loss of oxygen; oxidation is the gain of oxygen.
Equations and reacting masses
o In a balanced chemical equation there are the same number of atoms of each element on each side of the
equation.
o The relative atomic mass (RAM) of an element is the mass of the atom compared to the mass of an atom of
carbon (RAM 12). RAMs are given in the Periodic Table.
o The relative formula mass (RFM) of a compound is the sum of the RAMs of all the atoms or ions in its
formula.
o RFMs allow the calculation of the mass of metal that can be obtained from an ore.
Electrolysis
o Reactive metals may be extracted from their ores by electrolysis of the molten ionic compound.
o Positive metal ions move to the negative electrode; negative non-metal ions move to the positive electrode.
Metals and their uses
o The many useful properties of metals is a result of their structure and the strong metallic bond.
o The widespread use of metals has an undesirable impact on the environment..
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Checklist C5 Aiming for A
Use this checklist to see what you can do now. Refer back to pages 132–157 if you’re
not sure. Look across the rows to see how you could progress – bold italic means
Higher tier only.
Remember you’ll need to be able to use these ideas in many ways:
interpreting pictures, diagrams and graphs
applying ideas to new situations
explaining ethical implications
suggesting some benefits and risks to society
drawing conclusions from evidence you’ve been given.
Look at pages 300–306 for information about how you’ll be assessed.
Working towards an A grade
Aiming for Grade C
Aiming for Grade A
recall the names, symbols and formulas of elements and compounds that make
up air, and the percentages they make up in dry air
understand that in molecules of
non-metallic elements the atoms
are joined together by covalent
bonds; understand 2-D and 3-D
representations of bonds in
molecules
understand that the covalent bond
is caused by the attraction
between the positively charged
nuclei of atoms and a shared pair
of negatively charged electrons
understand that as molecules
are uncharged the forces
between them are weak and that
this explains the physical
properties of molecular
substances
understand that while the forces
between molecules are weak the
covalent bonds in the molecules are
strong
understand that the charged ions
in ionic compounds have a strong
force between them called the
ionic bond that results in the
properties of ionic compounds
work out the formulas of the
compounds dissolved in water,
given the charges on the ions
describe what happens when ionic
compounds form solutions
understand that a precipitate of
an ionic compound may be
formed when solutions
containing the ions are mixed
write ionic equations for these
precipitation reactions
understand the reactions that
produce an insoluble solid when
reagents are added to solutions
containing negative ions
given solubility data, predict when
a precipitate may be formed
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Aiming for Grade C
Aiming for Grade A
understand that strong covalent bonds between carbon atoms in diamond and
graphite, and between silicon and oxygen in silicon dioxide, form giant covalent
structures and how these different structures have particular physical properties
understand that in the reaction
for extracting a metal, the oxide
is reduced (loss of oxygen) and
carbon is oxidised (gains
oxygen)
explain that the extraction of metals
is an example of oxidation and
reduction occurring at the same time
write word equations from
information about a reaction;
recognise symbols of elements,
understand formulae of
molecules and ionic compounds,
and interpret symbol equations
balance unbalanced symbol
equations and write balanced
equations, including state
symbols
calculate relative formula
masses and calculate the mass
of a metal in the formula mass of
a compound
calculate the mass of a metal that
can be extracted from a mineral,
given the formula of the compound
or an equation
understand that in electrolysis of
molten ionic compounds, metals
are formed at the negative
electrode
use diagrams and ionic equations
to explain changes that occur at
the electrodes and in the
electrolyte in the electrolysis of
molten salts and molten
aluminium oxide
explain that the properties of
metals are due to the strong
metallic bond holding metal
atoms in a giant structure
understand that metal crystals are
made up of positive ions bound to
freely moving electrons
evaluate, given appropriate
information, the environmental
impact of the extraction, use and
disposal of metals on the
environment
develop arguments on the ethics of
the environmental impact of metals
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Checklist C5 Aiming for C
Use this checklist to see what you can do now. Refer back to pages 132–157 if you’re
not sure. Look across the rows to see how you could progress.
Remember you’ll need to be able to use these ideas in many ways:
interpreting pictures, diagrams and graphs
applying ideas to new situations
explaining ethical implications
suggesting some benefits and risks to society
drawing conclusions from evidence you’ve been given.
Look at pages 300–306 for information about how you’ll be assessed.
Working towards a C grade
Aiming for Grade E
Aiming for Grade C
recall the names, symbols and formulas of elements and compounds that make
up air, and the percentages they make up in dry air
recall that most non-metal
elements and compounds exist
as molecules
understand that in molecules of nonmetallic elements the atoms are
joined together by covalent bonds;
understand 2-D and 3-D
representations of bonds in
molecules
interpret data about the physical
properties of simple molecular
substances and recall that they
have low melting and boiling
points and do not conduct
electricity
understand that as molecules are
uncharged the forces between them
are weak and that this explains the
physical properties of molecular
substances
recall that the hydrosphere
consists largely of water which
contains dissolved salts
understand that the charged ions in
ionic compounds have a strong force
between them called the ionic bond
that results in the properties of ionic
compounds
understand that salts are ionic
compounds made up of ions,
which in the solid state form a
regular crystal lattice
describe what happens when ionic
compounds form solutions
understand that some metal ions
can be identified by the coloured
precipitate formed with an alkali
understand that a precipitate of an
ionic compound may be formed
when solutions containing the ions
are mixed
interpret the results for tests for
some negative ions in salts,
given a data sheet
understand the reactions that
produce an insoluble solid when
reagents are added to solutions
containing negative ions
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OCR 21st Century Science: C5 Checklist
Aiming for Grade E
recall that the lithosphere is made
up of minerals in which oxygen,
silicon and aluminium are the
most abundant elements
recall that diamond and graphite
are made up of carbon atoms
interpret data on the abundance
of elements
recall that ores contain minerals
from which metals can be
obtained
recall that copper, iron and zinc
can be extracted by heating their
oxides with carbon
Aiming for Grade C
understand that strong covalent
bonds between carbon atoms in
diamond and graphite, and between
silicon and oxygen in silicon dioxide,
form giant covalent structures and
how these different structures have
particular physical properties
understand that in the reaction for
extracting a metal, the oxide is
reduced (loss of oxygen) and carbon
is oxidised (gains oxygen)
write word equations from information about a reaction; recognise symbols of
elements, understand formulae of molecules and ionic compounds, and interpret
symbol equations
recall that relative atomic
masses compare the masses of
atoms of elements and can be
read off the Periodic Table
calculate relative formula masses
and calculate the mass of a metal in
the formula mass of a compound
understand that metals such as
aluminium can be obtained by
electrolysis of molten ionic
compounds, and that in this
process the compound is
decomposed by electricity
understand that in electrolysis of
molten ionic compounds, metals are
formed at the negative electrode
recall the properties of metals
and understand that their uses
relate to these properties
explain that the properties of metals
are due to the strong metallic bond
holding metal atoms in a giant
structure
describe the impact that the
extraction, use and disposal of
metals has on the environment
evaluate, given appropriate
information, the environmental
impact of metals
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_01 Molecules in the air
Resources
Student Book pages 132−133 Interactive Book: Drag and drop ‘Composition of air’; Naked Scientist animation ‘What is
covalent bonding?’ Homework pack c5_01
Files on Teacher Pack CD: c5_01_worksheet
Models or pictures of simple molecules
Learning outcomes
C5.1.1 recall that dry air consists of gases, some of which are elements (for example, oxygen, nitrogen and
argon) and some of which are compounds (for example, carbon dioxide)
C5.1.2 recall that the relative proportions of the main gases in the atmosphere are about 78% nitrogen, 21%
oxygen, 1% argon and 0.04% carbon dioxide
C5.1.3 recall the symbols for the atoms and molecules of these gases in the air
C5.1.4 recall that most non-metal elements and most compounds between non-metal elements are molecular
C5.1.9 understand that bonding within molecules is covalent and arises from the electrostatic attraction
between the nuclei of the atoms and the electrons shared between them
C5.1.11 translate between representations of molecules including molecular formulae, 2-D diagrams in which
covalent bonds are represented by lines, and 3-D diagrams for: a. elements that are gases at 20°C, b. simple
molecular compounds
Ideas about Science
IaS 3.1 scientific hypotheses, explanations and theories are not simply summaries of the available data – they are
based on data but are distinct from them
IaS 3.2 an explanation cannot simply be deduced from data, but has to be thought up creatively to account for the
data
Literacy focus: Sharing ideas and understanding about molecules and bonds.
Numeracy focus: Developing a sense of scale in the context of the Earth and its atmosphere; extracting
information from charts, graphs and tables including the abundance of elements on the Earth.
ICT focus: Using physical models and modelling software to show the shapes of molecules.
In this lesson students are learning to:
recall the elements and compounds that make up the air
explain that non-metallic elements and compounds form molecules
understand that in molecules the atoms are joined by covalent bonds.
Key vocabulary
dry air molecule covalent bond
Obstacles to learning
This topic moves swiftly from considering the names of gases in the air to understanding the bonds holding atoms
together in molecules. Some students may have difficulty in seeing the 3-D diagrams as 2-D projections of the
shape of molecules.
Stimuli and starter suggestions
Tell students that in this module they will be investigating the materials that make up land, sea and air. Ask them
to list the useful substances that we get from these:
air – oxygen (for welding, divers and medical uses); nitrogen (cooling); argon (lights); helium (balloons)
oceans, lakes and rivers – water, salt
land – fossil fuels, metals, limestone, rocks for building.
Note that these substances are solids, liquids and gases with different properties, which can be explained by the
way the atoms are joined together. Assess understanding of the terms ‘element’, ‘compound’, ‘mixture’, ‘solid’,
‘liquid’, ‘gas’ and ‘atom’.
Learning activities
worksheet c5_01
Low demand Ask students if they recall the gases that make up the air. Display the table of percentages
(Student Book p. 132) and explain why they refer to dry air (% of water vapour can vary from 0 to about 1 and
would affect all the other percentages if included). Check if they appreciate the difference in scale of the amounts
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c5_01 Molecules in the air continued
of N2 and O2 compared with CO2. For example if the 50 000 crowd in a football stadium were all molecules of air
then only about 20 of them would be CO2. Note that despite having a low percentage, CO2 has important effects
(greenhouse effect). Show models/diagrams and formulas of molecules of the substances. Explain what a
molecule is and note the difference between molecular elements and compounds, all of which are made up of nonmetals. Explain diatomic molecules. The worksheet provides tasks to reinforce this topic.
Teaching and learning notes: Test recall of the gases in the air from C1. Use tables and charts to relate the
names, formulae and percentages.
Standard demand Ask what holds molecules together. Show models/pictures of simple molecules (elements and
compounds). Explain that there is a bond between the atoms in a molecule (explain ‘bond’ as a force, glue,
attraction). Note that these bonds are called covalent bonds and that they hold a molecule together in a particular
shape. Show the various types of diagram that can be drawn for covalent molecules, explain how they are drawn
and what they show. Students could build models using kits. Explain the role of models and diagrams in helping to
visualise the theories based on, but not solely deduced from, data (e.g. the physical properties of the gases). The
worksheet provides tasks on this topic.
Teaching and learning notes: Students need to appreciate the difference between the 2D and 3D diagrams and
draw one, given the other, for simple molecular substances – they do not have to recall shapes of molecules.
High demand (Higher tier only) Ask what could hold the atoms together in a molecule. Discuss different types
of force (gravity, magnetism, electrostatic). Explain that a covalent bond is the electrostatic attraction between two
nuclei (+) and one, two or three pairs of electrons (−) shared between the atoms. Draw and explain dot and cross
diagrams and note that the shared electrons give the atoms the same electron arrangement as noble gases (they
may recall this from the work on ions in C4). Discuss the role of imagination and creativity in understanding
covalent bonding (but note that none of the diagrams or descriptions of a covalent bond at this level explains what
is happening to the electrons).
Plenary suggestions
Odd one out – ask students to pick out the odd one from the following trios (e.g.) and to say why it is different:
nitrogen, oxygen, carbon dioxide – carbon dioxide; compound
nitrogen, oxygen, argon – argon; monatomic
H2, O2, F2 – O2; has a double covalent bond
sketches of two 2-D and one 3-D molecules – 3-D; shows shape.
Student Book answers
Q1 O2
Q2 0.04%
Q3 a) Cl – Cl; b) Planar diagram as in Student Book p. 133
Q4 3D diagrams show the true shape of the molecule/the arrangement of the atoms in space, as well as the
arrangement of the bonds.
Q5 Hydrogen and oxygen atoms have a full outer shell; with the electron arrangements of noble gas atoms.
Q6 There is a bigger force between the nuclei and the shared electrons because there are four shared electrons;
unlike in chlorine where there are just two.
Worksheet answers
Activity 1 (Low demand)
Q1 a) water; b) nitrogen; c) argon; d) nitrogen, oxygen; e) carbon dioxide
Q2 a) A; b) C; c) B; d) D; e) all of them
Q3 Diagram with single atoms and a molecule with two different atoms
Activity 2 (Standard demand)
Q1 a) (Covalent) bonds; b) nitrogen, hydrogen; non-metals; c) 3-D diagram shows correct shape of molecule
Q2 a) Planar diagram; b) Diagram with arrow and dotted line to represent shape; c) Covalent bond
Q3 Diagram of O=O
Activity 3 (High demand)
Q1 a) Dot/cross diagrams showing one, two or three pairs of shared electrons as appropriate with correct number
of non-bonding electrons (outer shell only).
b) The nuclei of the atoms are attracted to the shared electron pair(s); this pulls and holds the nuclei together.
Q2 Dot/cross diagram for HCl
Q3 Dot/cross and 2-D diagrams for H2S; similar to water
Q4 2-D, 3-D and dot/cross diagrams similar to methane; with C replaced by Si
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_01 Molecules in the air
1
Air
1
a) Which substance that can make up to 1% of the air is missing from the chart?
...................................................................................................................................
b) Which gas makes up over three-quarters of dry air? ……………………………..….
c) Which gas in the air is made of molecules of single atoms? ………………………..
d) Which substances in the air are made up of diatomic molecules?
………………………………………………………………………………………………
e) Which substance in dry air is a molecular compound? ………………………………
2
Which box contains molecules:
a) of a pure element
……
b) of a pure compound
……
c) of a mixture of elements
……
d) of a mixture of an element and a compound
……
e) that are diatomic?
……
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c5_01 Molecules in the air continued
3
2
1
Sketch a diagram showing a mixture of an element made up of single atoms and a
diatomic molecular compound.
Molecules and models
The diagrams are models of ammonia molecules.
Ammonia is a gas room temperature.
a) What do the straight lines in the 2-D model
represent?
b) Name the elements that make up ammonia.
Are they metals, non-metals or both?
c) What does the 3-D diagram show that the 2-D
cannot show?
2
a) Draw a 2-D diagram to show the covalent bonds in methane.
b) Draw a 3-D diagram to show the shape of a methane molecule.
c) What is the name of the type of bond in methane molecules?
methane
3
3
1
Oxygen gas is made up of diatomic molecules with a double covalent bond.
Draw a 2-D diagram of the molecule.
Covalent bonds (Higher tier only)
Here are five elements that have diatomic molecules and are gases at room
temperature:
hydrogen, H2 (proton number = 1)
fluorine, F2 (9)
oxygen, O2 (8)
nitrogen, N2 (7)
chlorine, Cl2 (17)
a) Draw dot and cross diagrams to show the bonds in the molecules
b) Use one of your examples above to explain how the bond holds the atoms
together.
2
Hydrogen forms a simple molecular compound with each of the halogens (Group 7).
Draw a dot and cross diagram for hydrogen chloride, HCl.
3
Hydrogen sulfide is a molecule with a similar shape and bonds to water. Draw a 2-D
line diagram and a dot and cross diagram of hydrogen sulfide (proton number of sulfur
is 16).
4
Silane is a gas that has molecules resembling those of methane (CH4) but with the
carbon atoms replaced by silicon atoms. Draw 2-D and 3-D diagrams and a dot and
cross diagram of silane (proton number of silicon is 14).
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_02 Simple molecular substances
Resources
Student Book pages 134−135 Homework pack c5_02
Files on Teacher Pack CD: c5_02_worksheet; c5_02_technician
Equipment for demonstrations
Learning outcomes
C5.1.5 understand that molecular elements and compounds with small molecules have low melting and boiling
points
C5.1.6 interpret quantitative data (for example, melting and boiling points) and qualitative data about the
properties of molecular elements and compounds
C5.1.7 understand that molecular elements and compounds, such as those in the air, have low melting and
boiling points, and are gases at room temperature, because they consist of small molecules with weak forces of
attraction between the molecules
C5.1.8 understand that pure molecular compounds do not conduct electricity because their molecules are not
charged
C5.1.10 understand that covalent bonds are strong, in contrast to the weak forces of attraction between small
covalent molecules
Ideas about Science
IaS 3.1 scientific hypotheses, explanations and theories are not simply summaries of the available data – they are
based on data but are distinct from them
IaS 3.2 an explanation cannot simply be deduced from data, but has to be thought up creatively to account for the
data
Literacy focus: Using models to describe the theory of simple molecular substances.
Numeracy focus: Plotting, drawing and interpreting graphs and charts from students’ own and secondary data;
extracting information from charts, graphs and tables.
ICT focus: Modelling molecules and giant structures to explain properties; using animation to show the movement
of molecules in a gas over a range of temperatures.
In this lesson students are learning to:
use data about the properties of simple molecular substances
explain the properties of simple molecular substances
compare the forces between atoms in molecules and between molecules.
Key vocabulary
quantitative data qualitative data intermolecular intramolecular
Obstacles to learning
Students may have little sense of scale as to what constitutes a high or low melting or boiling point. Difficulty in
visualising the forces within and between molecules may leave students still confused as to why molecules do not
break up at their boiling points.
Stimuli and starter suggestions
What do you know and what would you like to know? Show some samples of simple molecular materials and ask
them to answer this question for each material. They can record appearance and they may know symbols and
formula. If they struggle guide them to realise that they need quantitative data such as melting points.
Learning activities
worksheet c5_02
Low demand Demonstrate to students the properties of some simple molecular substances (see technician
sheet). Display data/charts on the melting and boiling points of various simple molecular substances and note the
meaning of the terms ‘quantitative’ and ‘qualitative’. Ask if students can make any generalisations about these
substances – e.g. low melting and boiling points (What is ‘low’? – lower than room temperature, the boiling point of
water, a little higher?) and poor electrical conductivity. Draw students to conclude that all these substances have
similar properties because they have similar structures – i.e. all have small molecules. The worksheet gives further
tasks.
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c5_02 Simple molecular substances continued
Teaching and learning notes: Students need to read data from tables and charts and make comparisons
between data – e.g. high and low melting points in comparison to room temperature. Students will need to handle
negative Celsius temperatures.
Standard demand Show gas jars of oxygen and nitrogen and ask students to describe what they imagine is
happening in the gases. Discuss what happens when the gases are cooled to their condensation and freezing
points. Do they bring up the idea of (weak) forces pulling the molecules together? Note that this visualisation is an
important part of producing a theory that is not just a matter of looking at the data. Show an animation of the effect
of temperature on the molecules in a gas. Guide students to the conclusion that the forces between simple
molecules are weak. Similarly account for the poor conductivity of simple molecular substances (no charged
particles to move freely). The worksheet gives further tasks on this.
Teaching and learning notes: Students should be familiar with the kinetic theory of matter and models of the
states of matter. This can be reinforced with emphasis on change of state and the magnitude of forces between
particles, particularly in the solid and liquid states.
High demand Discuss the difference between the magnitude of intermolecular and intramolecular forces in
simple molecular substances. Note that a temperature in excess of 1000 °C is needed to break the covalent bonds
water molecules – there are strong force of attraction between nuclei and shared electrons. (An extra consideration
here is that temperature is a measure of the average kinetic energy of particles.) Hence explain that covalent
bonds are very strong.
Plenary suggestions
Ask students to summarise what they have learned about simple molecular substances – e.g. where are they found
naturally on Earth (in the air), type of elements, formulae, covalent bonds and diagrams, properties, explanations
for properties. This could be done by students writing down one point, sharing with a neighbour, then the pairs
sharing with a group to build up a list of features of simple molecular substances.
Student Book answers
Q1 Nitrogen
Q2 Disappears/ turns to solid (accept liquid) carbon dioxide
Q3 Methane has small molecules with weak forces between them
Q4 Hydrogen chloride; it has low boiling point/ is a gas at room temperature
Q5 The positive and negative charges inside the molecule are balanced; the molecule is neutral so is not affected
by an electric current
Q6 The forces between water molecules are relatively weak; little energy is needed to separate them into a gas.
The covalent bonds in water molecules are strong; much more energy is needed to break the bonds and free
the hydrogen and oxygen atoms.
Worksheet answers
Activity 1 (Low demand)
Q1 A series of cards (like the one shown); PowerPoint pages, etc.
Q2 a) Bar chart; one quantitative variable and one categoric
b) Hydrogen, phosphorus, chlorine, oxygen, nitrogen; have low boiling points and do not conduct electricity
c) Non-metal elements
Activity 2 (Standard demand)
Q1 Observations (see technician sheet); ethyl ethanoate has a low boiling point and is a non-conductor.
Q2 Room (high) temperature – particles moving randomly and colliding in large volume, small forces between
particles; Low temperature – particles clustered together in smaller volume, forces same size as before
Q3 a) and c) are true; b) Simple molecular substances are poor conductors …
d) The weak forces between … give molecular substances low …
e) … have boiling points below room temperature
Activity 3 (High demand)
Q1 Should show two molecules that each have two or more atoms joined by strong covalent bonds that do not
break easily; but there are weak forces between the molecules that can be overcome easily.
Q2 Boiling just overcomes the weak forces between the molecules; the covalent bonds are much stronger and
need a lot more energy to break them to separate the atoms.
Q3 a) Oxygen gas is still made up of O2 molecules; not O atoms.
b) In a molecule the positive and negative charges are balanced/number of protons is equal to the number of
electrons; so the molecule has no overall charge and is not attracted to an electric charge/electrode.
COLLINS NEW GCSE SCIENCE
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_02 Simple molecular substances
Technician sheet
Equipment and materials
Demonstration
gas jars labelled ‘nitrogen’ and ‘oxygen’ – they don’t have to contain the gases
ethyl ethanoate
sulfur
iodine
liquid nitrogen or dry ice would be useful
power pack (0–12 V)
leads and crocodile clips
carbon electrodes
light bulb in holder; or ammeter
Bunsen burner, tripod and water bath; or heating mantle
small evaporating dish
thermometer
spatula
Method
1
Show that some substances change state with little or no heating – liquid nitrogen, dry
ice, sulfur, iodine. Heat a little sulfur or iodine – on a spatula in a fume cupboard.
2
In a fume cupboard, warm about 5 cm3 of ethyl ethanoate in a boiling tube and
measure the temperature at which it boils – record the temperature.
3
In a fume cupboard, set up an electric circuit using two carbon electrodes in a holder, a
power pack and a light bulb or ammeter. Check that the circuit works. Hold the
electrodes in an evaporating dish containing cold ethyl ethanoate. Turn on the power –
note that no current flows. Make sure that the electrodes do not short and cause a spark.
Notes
Ethyl ethanoate boils at 77 °C. It is used as nail-varnish remover and as a flavouring. It
is safer to use than propanone. It does not conduct electricity.
Melting point of sulfur is 113 °C.
Iodine melts at 114 °C and boils at 184 °C. The liquid stage is usually missed when it is
heated in a Bunsen burner flame.
Health and Safety
Ethyl ethanoate is HIGHLY FLAMMABLE, so will require very careful heating. Carry out
the tests on ethyl ethanoate in a fume cupboard.
Sulfur is FLAMMABLE and produces TOXIC fumes when burning – heat in a fume
cupboard (if a CLEAPSS member, read the Model Risk Assessment on Hazcard 96A).
Iodine is TOXIC and produces a toxic vapour when heated – heat it in a fume cupboard
and do not allow students to touch it (if a CLEAPSS member, read the Model Risk
Assessment on Hazcard 54A).
Liquid nitrogen and dry ice are extremely cold – do not allow either to touch the skin.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_02 Simple molecular substances
1
1
Looking at data
Design a virtual exhibition of substances made up of
simple molecules.
Use qualitative data such as appearance and whether
the substance conducts electricity, and quantitative data
such as melting and boiling points.
Make sure you show the things that are similar about
simple molecular substances.
Photo: © Andrew Lambert Photography/Science Photo Library
2
The table below gives some data about various elements.
Substance
Hydrogen
Boiling point (°C)
Conduct electricity in
the solid or liquid state?
−253
no
Phosphorus
280
no
Magnesium
1107
yes
Chlorine
−25
no
Oxygen
−183
no
Nitrogen
−196
no
907
yes
Zinc
a) What would be the best way to display this data to show the differences between
substances? Display the data in the way you suggest.
……………………………………………………………………………………………
……………………………………………………………………………………………
b) Which elements in the table are probably made up of simple molecules? Explain
your answer.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
c) What does your answer to part (b) suggest is the type of element that has simple
molecules?
……………………………………………………………………………………………
……………………………………………………………………………………………
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c5_02 Simple molecular substances continued
2
Forces between molecules
1
Make observations and note some data about ethyl ethanoate. Compare ethyl
ethanoate with the other substances shown to you. Prepare an evidence file to show
that ethyl ethanoate is a simple molecular substance.
2
Sketch a storyboard (a series of diagrams) showing what happens to the molecules
when a gas cools to below its condensation (boiling) temperature. Label the diagrams
with the forces acting between molecules.
3
Which of the following are true statements about simple molecular substances? Write
corrections of the false statements to make them true for simple molecular substances.
a) Elements and compounds can be simple molecular substances.
b) Simple molecular substances are good conductors of electricity in the solid and
liquid states.
c) Simple molecular substances are made up of small molecules.
d) The strong forces of attraction between small molecules give molecular substances
high melting and boiling points.
e) Simple molecular substances found in the air have boiling points above room
temperature.
3
Forces within and between molecules
1
How could you show someone less experienced in science than yourself the difference
between the size of the forces between molecules and the forces between the atoms in
a molecule? (You could draw diagrams, construct models, devise a role-play drama or
dance).
What are the main points that you need to make about simple molecular substances?
2
William says that steam is a mixture of hydrogen and oxygen atoms because when
water boils at 100 °C the weak covalent bonds in water molecules break apart.
What is wrong with William’s idea? What is the correct story?
3
a) What evidence is there that oxygen molecules have strong bonds – even though it
boils at −183 °C?
b)
If covalent bonds are the attraction between positively charge nuclei and
negatively charged electrons, why don’t simple molecular substances conduct
electricity?
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_03 Ionic crystals
Resources
Student Book pages 136−137 Interactive Book: Matching pairs ‘Identifying ionic compounds’ Homework pack c5_03
Files on Teacher Pack CD: c5_03_worksheet; c5_03_practical; c5_03_technician
Equipment for practical
Learning outcomes
C5. 2.1 recall that the Earth’s hydrosphere (oceans, seas, lakes and rivers) consists mainly of water with some
dissolved compounds, called salts
C5.2.2 understand that the ions in crystals of a solid ionic compound are arranged in a regular way forming a
lattice
C5.2.3 understand that ions in a crystal are held together by forces of attraction between oppositely charged ions
and that this is called ionic bonding
C5.2.4 understand how the physical properties of solid ionic compounds (melting point, boiling point, electrical
conductivity) relate to their bonding and giant, three-dimensional structures
C5.2.5 describe what happens to the ions when an ionic crystal dissolves in water
C5.2.6 explain that ionic compounds conduct electricity when dissolved in water because the ions are charged
and they are able to move around independently in the solution
C5.2.7 work out the formulae for salts in seawater given the charges on ions (for example sodium
chloride, magnesium chloride, magnesium sulfate, sodium sulfate, potassium chloride and potassium
bromide)
Ideas about Science
IaS 3.1 scientific hypotheses, explanations and theories are not simply summaries of the available data – they are
based on data but are distinct from them
IaS 3.2 an explanation cannot simply be deduced from data, but has to be thought up creatively to account for the
data
Literacy focus: Using theory to explain observations.
Numeracy focus: Developing a sense of scale in the context of the Earth; plotting, drawing and interpreting graphs
and charts from students’ own and secondary data; extracting information from charts, graphs and tables including
the abundance of elements on the Earth.
ICT focus: Modelling giant structures to explain properties; using modelling software to illustrate ionic structures
In this lesson students are learning to:
recall that salts are ionic compounds that are found dissolved in water on the Earth’s surface
understand that the ions in ionic compounds are arranged in a lattice structure held together by ionic bonds
explain how the properties of ionic compounds depend on the forces between ions and the arrangement of the
ions in the crystal lattice.
Key vocabulary
hydrosphere salts crystals ionic compounds lattice ionic bond molecular ion
Obstacles to learning
Many compounds are ionic but are not found in seawater, are insoluble in water and do not have ‘simple’ melting
and boiling points (they decompose). These examples could confuse students.
Stimuli and starter suggestions
Ask students to make a list of things that they know about seawater and think that they would like to know about
seawater. They can swap their knowledge and questions. Elicit whether or not they understand that seawater is a
mixture of dissolved compounds and elements, including simple molecular substances such as oxygen and
carbon dioxide, and salts such as sodium chloride.
Learning activities
worksheet c5_03 + practical c5_03
Low demand Ask students to name some of the types of places where they may find water on the Earth. Remind
them that water can be solid, liquid or gas – e.g. ice caps and glaciers, oceans, lakes, rivers, aquifers, clouds, air.
The hydrosphere includes all the solid and liquid water. Ask students to suggest how we could show that a sample
of water contains dissolved solids – evaporation (not by tasting). Explain that the solid formed is probably a salt.
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c5_03 Ionic crystals continued
Explain the terms ‘salt’, ‘ion’, ‘crystal lattice’, ‘giant structure’. See the practical sheet for the procedure to grow
crystals.
Teaching and learning notes: In C4 students met ions, ionic compounds and crystal lattice structures – assess
their understanding of these ideas. The practical on making crystals is probably more suited to lower-attaining
students because it takes a considerable time.
Standard demand Follow this with a study of the properties of ionic compounds such as sodium chloride (melting
and boiling point). Discuss electrical conduction by ionic compounds (demonstrations in c4_11 and 12). If there is
time students could research data on a variety of ionic compounds and build up a virtual exhibition as they did for
the molecular substances. Invite them to offer an explanation for the properties – i.e. strong forces between the
ions in the lattice; that requires a lot of energy to disturb; and incompressibility. Explain that the force is due to the
attraction between positive and negative ions. Show computer models and animations, or build up the NaCl
structure by adding more and more ions to make a giant ionic lattice.
Teaching and learning notes: Ideas about ions need to be extended to explain the properties of ionic
compounds, as compared with the simple molecular materials met in previous lessons.
High demand (Higher tier only) Explain that the formula of an ionic compound gives the ratio of the numbers of
positive ions and negative ions. Remind students that that an ionic compound has no overall charge so the positive
and negative charges are balanced. Hence, show how to work out a formula (covered in c4_12). Explain the term
‘molecular ion’ and show how they are used in formulae – e.g. sulfate, nitrate, carbonate. This can be related back
to the hydrosphere and composition of salt water. See the worksheet.
Plenary suggestions
Ask students to examine the labels of mineral water bottles. Make a list of the (ionic) compounds present (by
combining positive and negative ions). Higher tier students could work out the formulas.
Student Book answers
Q1 Oceans, seas, lakes, rivers
Q2 Evaporate the water
Q3 Strong forces of attraction between the sodium and chloride ions; a lot of energy/high temperature needed to
disturb the ions.
Q4 Sodium and chloride ions are trapped/ fixed in the solid; are free to move when dissolved in water.
Q5 a) NaBr; b) CaCl2; c) MgSO4; d) K2SO4
Worksheet answers
Activity 1 (Low demand)
Q1 a) glaciers; b) oceans; c) rivers and lakes; d) oceans
Q2 a) ions; b) Regular pattern of rows and columns; c) Pattern is repeated over and over again to build up the
crystals; d) Heat the seawater to evaporate the water
Activity 2 (Standard demand)
Q1 a) Nickel; a metal that conducts in the solid state; ethanol; simple molecule; non-conductor with low m.p.
b) High m.p. and b.p.; non-conductor in solid state; conductor in liquid state and in solution.
Q2 a) Ions not large; regular structure repeats many times with many billions of ions.
b) Ions don’t ‘stick’; positive and negative ions are attracted by electrostatic force.
c) Crystal shapes vary with the relative numbers of ions; and the sizes of the ions.
d) Ions do not lose their charge; energy needed to overcome the attractive force between the ions.
e) Charges do cancel; but the solid does not conduct because the ions are not free to move.
f) Dissolves; water molecules cluster round the ions separating them; allowing them to move freely.
g) Data itself does not give much information about what an ionic compound is; imagination and creativity can
help to produce a theory; that makes predictions that can be tested.
Activity 3 (High demand)
Q1 NaCl, Na2SO4, Na2CO3, NaBr, MgCl2, MgSO4, MgCO3, MgBr2, CaCl2, CaSO4, CaCO3, CaBr2, KCl, K2SO4,
K2CO3, KBr
Q2 The sulfate is said to be molecular because it has S and O atoms joined by covalent bonds; it is an ion because
it has an overall negative charge/it has gained two extra electrons.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_03 Ionic crystals
P
Making large crystals
Objectives
In this activity you will:
prepare large crystals of an ionic compound
examine the shapes of various ionic compounds.
Some ionic compounds are toxic or irritants. Wear goggles throughout the
experiment and avoid contact with the skin.
Equipment and materials
• beakers (small and large) • crystallising dish • Bunsen burner, tripod, gauze
• samples of soluble ionic compounds • distilled water • spatula • glass rod • fine thread
Method
Part A – making the seed crystals
1
Half fill a small, clean beaker with distilled water.
2
Put the beaker on the tripod and gauze, and warm the water.
3
Take the beaker off heat and add a spatula of the ionic compound you are going to
make into crystals. Note the name of the solute you are using.
4
Stir the mixture until all the solid dissolves. Add more solid and stir again. Repeat this
until some of the solid will not dissolve. The solution is now saturated with the solute.
5
Pour the saturated solution into the crystallising dish. Put the dish somewhere away
from draughts and where the temperature will remain fairly constant.
6
Examine the contents of the dish every day until all the water has evaporated.
Part B – making the crystal larger
7
Use a large beaker to make up a saturated solution of your ionic compound (see steps
1–5). Let the solution cool.
8
Choose the largest of your crystals (from step 6) with a good, regular shape.
9
Tie a length of fine thread around your crystal. Hang it from the glass rod in the
saturated solution (step 7).
10 Leave your beaker and crystal for a few weeks. You may have to top up the beaker
with saturated solution every week or so. Do not add water to the beaker (your crystal
may dissolve).
Results
Sketch the shape of your new crystal(s). Measure and record the length each week.
Questions
1
What are the meanings of the terms ‘solution’, ‘solute’ and ‘saturated’?
2
Describe and explain what happens when an ionic crystal is put in water.
3
Why do different ionic compounds have different shaped crystals?
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_03 Ionic crystals
Technician sheet
Equipment and materials
Each group will need:
beakers – 100 cm3 and 250 cm3
crystallising dish – or evaporating dish, watch glass, etc.
Bunsen burner, tripod and gauze
fine thread
spatula
glass rod
hydrated copper sulfate – powdered
alum (potassium aluminium sulfate) – powdered
magnesium sulfate – powdered
distilled water
Method
Full instructions are given on practical sheet c5_03.
Notes
Health and Safety: copper sulfate is TOXIC by ingestion; potassium aluminium sulfate
(alum) is an IRRITANT. Wear goggles. If a member of CLEAPSS, refer to Hazcard 2B.
Producing large crystals takes a long time (weeks) and is expensive in materials
(especially copper sulfate). The method describes how to produce small, regular
shaped crystals (in a day or so) before going on to grow large crystals. The procedure
can initially involve just the first stage. The second stage can carried out as a class or
group task using the best of the small crystals formed.
This task may be more suitable for Foundation tier candidates.
It would be interesting to use a variety of compounds to show the different crystal
structures.
Note how small crystals grow into larger crystals maintaining the same shape. This
illustrates the idea of ‘giant ionic crystals’.
The method described does not work well for sodium chloride. Sodium chloride is
hygroscopic. Crystals exposed to moist air will absorb water, losing their sharp crystal
shape. Sodium chloride crystals, large enough to see the cubic shape, can be grown by
hanging a wire in a saturated sodium chloride solution.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_03 Ionic crystals
1
1
The hydrosphere
This is a list of the parts of the hydrosphere:
oceans
rivers
glaciers
lakes
Choose your answers to these questions from these words.
a) Where in the hydrosphere can you find water in the solid state? .............................
b) Which part of the hydrosphere contains the most dissolved salts? ..........................
c) Which part(s) of the hydrosphere do we use as a source of fresh water?
................................................................................................................................
d) Which part of the hydrosphere contains most of the water on the Earth? ................
2
The diagram shows part of the crystal lattice of sodium chloride:
a) What are the particles that make up sodium chloride called? ..................................
b) Why is the pattern called a ‘lattice’? ........................................................................
................................................................................................................................
c) A crystal of sodium chloride is called a giant ionic lattice. What does the word
‘giant’ mean?
................................................................................................................................
d) How could you make crystals of sodium chloride from seawater?
................................................................................................................................
................................................................................................................................
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c5_03 Ionic crystals continued
2
1
Ionic compounds and ionic bonds
Look at the data in the table:
Substance
Melting point (°C)
Sodium chloride
Boiling point (°C)
Does it conduct electricity?
801
1413
Only when liquid or in solution
Calcium oxide
2614
2850
Only when liquid or in solution
Nickel
1455
2730
In the solid or liquid state
Potassium iodide
681
1330
Only when liquid or in solution
Magnesium bromide
700
1230
Only when liquid or in solution
−117
78
Ethanol
No
a) Which substances are probably not ionic compounds? Give your reasons.
b) What properties are typical of ionic compounds?
c) Find out more facts about the ionic compounds listed above and other ionic
compounds. Design a virtual exhibition of data on various ionic compounds.
2
You have been asked to explain the properties of ionic compounds to a group of
students who have some confused ideas – here are some of the ideas they have:
a) Sodium chloride is called a giant ionic structure because it is made up of very large
ions.
b) An ionic crystal is made by sticking ions together.
c) All ionic crystals have the same shape lattice.
d) Ionic crystals have high melting and boiling points because it takes a lot of energy
to take the charges away from the ions.
e) Solid ionic substances do not conduct electricity because the charges on the ions
cancel out.
f)
An ionic crystal melts when it is put in water.
g) There is no place for imagination in chemistry. Ionic theory is all about measuring
quantities such as melting points.
Give correct explanations using the theory of ions. You can use diagrams if you wish.
3
1
Ions and formulae
Seawater is a mixture containing many different ions. When evaporated to dryness,
over 99% of the solid formed is made up of the following ions:
sodium (Na+)
magnesium (Mg2+) calcium (Ca2+)
potassium (K+)
chloride (Cl−)
sulfate (SO42−)
bromide (Br−)
carbonate (CO32−)
Name and write the formula of all the compounds that could be obtained from
seawater. (Hint: there are sixteen possible compounds.)
2
The sulfate ion, SO42−, is called a molecular ion.
How can something be both a molecule and an ion?
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_04 Testing metal ions
Resources
Student Book pages 138−139 Interactive Book: Practical investigations ‘Flame tests’; Matching pairs ‘Testing for ions’
Homework pack c5_04
Files on Teacher Pack CD: c5_04_practical; c5_04_technician
Equipment for practical
Learning outcomes
C5. 2.8 understand that the ions in an ionic compound can be detected and identified because they have distinct
properties and they form compounds with distinct properties
C5.2.9 understand that an insoluble compound may precipitate on mixing two solutions of ionic compounds
C5.2.10 be able to write ionic equations for precipitation reactions when given appropriate information
C5.2.11 interpret given information on solubility to predict chemicals that precipitate on mixing solutions
of ionic compounds
C5.2.12 understand that some metal ions can be identified in solution by adding alkali because they form insoluble
hydroxides with characteristic colours
C5.2.13 interpret the results of adding aqueous sodium hydroxide to solutions of salts, given a data sheet of tests
for positively charged ions and appropriate results
Candidates will be given a qualitative analysis data sheet showing tests for positively charged ions.
Literacy focus: Following instructions and describing observations.
Numeracy focus: Balancing ionic equations.
ICT focus: Viewing animations of ions in solutions forming precipitates.
In this lesson students are learning to:
understand how precipitates can be formed when two solutions are mixed
identify the metal ion in a salt
write equations for precipitation reactions.
Key vocabulary
precipitate insoluble ionic equation
Obstacles to learning
Some students have difficulty in understanding that the metal ions give the same results with sodium hydroxide
regardless of what other ions are in solution.
Stimuli and starter suggestions
This topic could be given a forensic science slant. Give the students the following information – a murder has
been committed and there are five suspects. A is a plasterer working with calcium sulfate; B is a gardener who
has been using copper sulfate as a fungicide; C works in an electronics factory using iron(III) chloride to prepare
printed circuit boards; D is a carpenter using iron(II) sulfate to stain wood; E was recycling the zinc compounds
from batteries. The murderer left traces of a substance at the scene of the crime and the scientists have made a
solution using it. How can they identify the killer? Discuss the problem with students – they may recall that flame
tests can be used to identify some metal ions, but not in this case.
Learning activities
practical c5_04
Low demand Explain that scientists often need to know what metal ions are present in samples – e.g. mineral
water, food, hair – and that there are some simple tests we can do to identify the ions present. Give out the
practical sheet and if necessary go through the procedure. Students can work in pairs to carry out the tests on the
five known and two unknown solutions. Discuss their observations – make sure they match the observations given
in the specification – and how they can be used to identify the ions in unknown solutions. Explain the term
‘precipitate’. Note that the tests work because the ions have properties independent of the other ions present.
Teaching and learning notes: Students will need practice interpreting the results of the test and can be given
copies of the test chart.
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c5_04 Testing metal ions continued
Standard demand Explain the precipitation of insoluble ionic compounds from the mixing of two solutions of ions.
An animation would be useful – or students can make storyboards showing their own cartoons on what happens
when the solutions mix. There are further questions on the practical worksheet relating to the reactions.
Teaching and learning notes: There is no expectation that students will understand why the zinc precipitate
dissolves on addition of excess sodium hydroxide, nor is there any requirement to draw attention to the variable
valency of iron.
High demand Explain that an ionic equation is one that shows the ions taking part in a chemical reaction with the
numbers of each ion present. Go through the mechanism for writing ionic equations, eliminating spectator ions.
Also work backwards from the ionic equation to a reaction between two soluble compounds including other
examples of precipitation reactions. The practical worksheet gives further exercises.
Plenary suggestions
Look back at the murder scenario given in the starter. Ask students to suggest what result would be obtained if
each of the suspects turned out to be the murderer. You could then say that one (or both) of the unidentified
samples in the practical exercise was the sample from the murderer and hence they can identify who it was.
Student Book answers
Q1 Contain copper (ions)
Q2 Iron(II), Fe
2+
3+
Q3 Iron(III); Fe ; iron(III) ions combine with hydroxide ions to form insoluble iron(III) hydroxide.
Q4 Make a solution of the unknown compound; add NaOH until in excess; a white precipitate forms; add excess
NaOH; precipitate dissolves.
3+
−
Q5 Fe (aq) + 3OH (aq) → Fe(OH)3(s)
Q6 Mix solutions of lead(II) nitrate and sodium iodide.
Practical sheet answers
Q1 A white precipitate (calcium hydroxide)
Q2 Zinc
Q3 Iron(II)
Q4 Red-brown precipitate; of iron(III) hydroxide
Q5 Mix solutions of zinc nitrate and sodium carbonate.
2+
−
Q6 (H) a) Fe (aq) + 2OH (aq) → Fe(OH)2(s)
2+
−
b) Pb (aq) + 2Cl (aq) → PbCl2(s)
3+
3−
c) 2Al (aq) + 3CO
2+
(aq) → Al2(CO3)3(s)
−
Q7 (H) (1) Ca (aq) + 2OH (aq) → Ca(OH)2(s)
2+
−
2+
−
3+
−
2+
2−
(2) Zn (aq) + 2OH (aq) → Zn(OH)2(s)
(3) Fe (aq) + 2OH (aq) → Fe(OH)2(s)
(4) Fe (aq) + 3OH (aq) → Fe(OH)3(s)
(5) Zn (aq) + CO3 (aq) → ZnCO3(s)
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_04 Testing metal ions
P
Testing solutions containing metal ions
Objectives
In this activity you will:
learn to carry out tests to identify some metal ions in solution
identify the unknown metal ion in some solutions.
Sodium hydroxide solution is an IRRITANT – wear goggles.
Some of the metal ions are TOXIC – do not ingest any.
Clear up spills.
Equipment and materials
• test tubes and test tube rack • droppers • sodium hydroxide solution
• solutions containing metal ions – calcium, copper, iron 2+, iron 3+ and zinc
• unidentified solutions X and Y
Method
1
Pour about 2 cm3 of one of the metal ion solutions into a clean test tube. Note which
metal ion it is.
2
Add sodium hydroxide solution drop by drop. Record what you see.
3
Shake the test tube to mix the solutions thoroughly.
4
Continue adding drops of sodium hydroxide solution and shaking until you have added
the same volume of sodium hydroxide. Record what you see.
5
Empty the test tube and wash it thoroughly.
6
Repeat all this for each of the metal ion solutions provided.
7
Use the same method to test the unidentified solutions X and Y.
Results
Record your observations in a table and identify the metal ions in solutions X and Y.
Questions
1 Calcium is the second most common metal ion in seawater. What would you expect to
happen if seawater was tested with sodium hydroxide solution? (The sodium ions have
no effect.)
2 A solution of a substance used to control the growth of moss on houses was tested with
sodium hydroxide solution. A white precipitate was formed that dissolved when extra
sodium hydroxide was added. What metal ion is in the moss killer?
3 Peter was feeling unwell – his doctor told him to take some tablets. Peter decided to
test a tablet and dissolved it in water. When he added some sodium hydroxide solution,
a green precipitate was formed. What metal ion was in the tablets?
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c5_04 Testing metal ions continued
4 Look at the equation shown below. What would you expect to see in this reaction?
Explain your answer.
FeCl3(aq) + 3NaOH(aq) → Fe(OH)3(s) + 3NaCl(aq)
5 Zinc carbonate is used as a white pigment. Describe how you could make zinc
carbonate. (Hint: most carbonates are insoluble in water. All sodium compounds and all
nitrates are soluble.)
Extension (Higher tier only)
6 Balance the following ionic equations:
a) … Fe2+(aq) + … OH−(aq) → … Fe(OH)2(s)
b) … Pb2+(aq) + … Cl−(aq) → … PbCl2(s)
c) … Al3+(aq) + … CO32−(aq) → … Al2(CO3)3(s)
7 Write ionic equations for the formation of the precipitates in questions 1 to 5.
Formula of ions: calcium Ca2+, copper Cu2+, iron(II) Fe2+, iron(III) Fe3+, zinc Zn2+,
hydroxide OH−, carbonate CO32−
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_04 Testing metal ions
Technician sheet
Equipment and materials
Each group will need:
test tubes (×7)
test tube rack
droppers – or dropping bottles
sodium hydroxide solution (0.5 mol dm−3) – approx. 20 cm3 per group
about 2 cm3 per group of 0.1 mol dm−3:
– calcium chloride labelled ‘Solution containing calcium ions’
– copper(II) sulfate labelled ‘Solution containing copper ions’
– iron(II) sulfate labelled ‘Solution containing iron 2+ ions’
– iron(III) chloride labelled ‘Solution containing iron 3+ ions’
– zinc chloride labelled ‘Solution containing zinc ions’
solutions in bottles marked ‘Solution X’ and ‘Solution Y’
Method
Full instructions are given on practical sheet c5_04.
Notes
Health and Safety: sodium hydroxide solution is an IRRITANT at the concentration
suggested – wear goggles. Copper ion solutions are TOXIC by ingestion.
It is important that the solutions are not contaminated. It is better to use dropping bottles
instead of loose droppers. If pairs of students can be supplied with sufficient amounts of
each solution then the waste of chemicals can be reduced.
The volume of the test solution is not critical. Students should not need to measure out
2 cm3 – about a 2 cm depth in a test tube is sufficient.
If there is a limited supply of test tubes, students must clean the tubes thoroughly
between tests.
Bungs can be provided to stopper the test tubes for mixing, but care must be taken to
prevent the bungs contaminating the solutions. Show students how to shake test tubes
from side to side without spillage or the need for a bung.
If the iron(II) solution is stabilised by addition of acid (to prevent oxidation) then students
will need to add a larger amount of sodium hydroxide to see the precipitate.
The expected results are given in Appendix G of the specification and on Student Book
p.138. If some of the iron(II) has oxidised it will give a brownish-green precipitate.
The tests can be done on a smaller scale using dimple trays. The only problem is
adding excess sodium hydroxide when testing for zinc ions.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_05 Analysing salts
Resources
Student Book pages 140−141 Homework pack c5_05
Files on Teacher Pack CD: c5_05_practical; c5_05_technician
Equipment for practical
Learning outcomes
C5.2.10 be able to write ionic equations for precipitation reactions when given appropriate information
C5. 2.14 understand that some negative ions in salts can be identified in solution by adding a reagent that reacts
with the ions to form an insoluble solid
C5.2.15 interpret the results of tests for carbonate, chloride, bromide, iodide and sulfate ions given a data sheet of
tests for negatively charged ions and appropriate results (using dilute acid, limewater, silver nitrate and barium
chloride or barium nitrate as the reagents)
Candidates will be given a qualitative analysis data sheet showing tests for negatively charged ions.
Literacy focus: Following written instructions and recording observations.
In this lesson students are learning to:
describe and explain tests to identify the negative ions in salts
write ionic equations for the reactions in the tests.
Key vocabulary
effervescence
Obstacles to learning
The importance of negative results – e.g. no fizzing means no carbonate – can make these tests confusing.
Stimuli and starter suggestions
This lesson could be introduced with another forensic scenario. Yet another murder has been committed with five
suspects, one of whom left a sample of a powder at the crime scene. Suspect A works in a limestone quarry;
suspect B says she was recharging the home water softener with salt (sodium chloride); suspect C is an amateur
photographer using potassium bromide to make his own photographic paper; suspect D works at a nuclear
power station and was preparing potassium iodide tablets for use in a nuclear emergency; suspect E is a tomato
farmer who says he was putting magnesium sulfate fertiliser on his crop. Discuss how the murderer could be
discovered.
Learning activities
practical c5_05
Low demand Remind students that ionic compounds (salts) are made up of positive ions and negative ions. In
the previous lesson they learned about tests for the positive metal ions – now it is the turn of the negative ions. Go
through the procedure on the practical sheet. Students should observe the result of tests on the five known ions,
and one or two unknown solutions. They should record their observations – make sure that these match the
observations in Appendix G of the specification and as given in Student Book p.140.
Teaching and learning notes: Some students will need assistance in carrying out the sequence of tests.
Standard demand Discuss what is happening at each stage of the tests and write word equations. Discuss the
different solubilities of salts – in particular that silver halides are insoluble whereas barium halides are soluble, and
vice versa for the sulfates. The practical sheet gives further questions for students to answer.
Teaching and learning notes: Students may recall earlier work on the reactions of acids with carbonates. The
ionic equation is not required but they should understand the word equation and symbol equations for the reaction
of a named metal carbonate with nitric acid.
High demand Students should write ionic equations for the precipitation of each of the ions in the tests. They
should be able to cope with solutions containing a mixture of negative ions. There are some Higher tier questions
on the practical sheet.
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c5_05 Analysing salts continued
Plenary suggestions
Complete the murder scenario from the starter. If there is time summarise the tests on both positive ions and
negative ions. Ask students to explain how they could show that a sample contains calcium chloride, iron(II)sulfate,
zinc bromide, etc. This could be a practical exercise with students given samples of the salts, which they dissolve
in water.
Student Book answers
Q1 Contains carbonate ions
Q2 Contains sulfate ions
Q3 No effervescence; yellow precipitate is formed; precipitate of silver iodide formed.
Q4 Bromide ion; precipitate of silver bromide formed
+
−
Q5 a) Ag (aq) + Br (aq) → AgBr(s)
−
b) Ag+(aq) + I (aq) → AgI(s)
2+
2−
c) Ba (aq) + SO4 (aq) → BaSO4(s)
Practical sheet answers
Q1 Compare with specification Appendix G and Student Book p.140.
Q2 Answer depends on which solutions were chosen as X and Y.
Q3 Bromide ions, Br
−
Q4 Sulfate ions, SO4
2−
Q5 It would fizz when nitric acid was added, showing the presence of carbonate ions; give a white precipitate with
silver nitrate showing the presence of chloride ions; and a white precipitate with barium ions showing the
presence of sulfate ions.
+
−
Q6 (3) Ag (aq) + Br (aq) → AgBr(s)
2+
2−
(4) Ba (aq) + SO4 (aq) → BaSO4(s)
+
2−
(5) [CO3 (s) + 2H (aq) → CO2(g) + H2O(l), but no precipitate formed]
+
−
Ag (aq) + Cl (aq) → AgCl(s)
2+
2−
Ba (aq) + SO4 (aq) → BaSO4(s)
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_05 Analysing salts
P
Testing the negative ions in salts
Objectives
In this activity you will:
learn to carry out tests to identify some negative ions in solution
identify the unknown negative ion in some solutions.
Nitric acid is CORROSIVE – wear goggles throughout the experiment.
Equipment and materials
• test tubes, test tube rack • droppers • nitric acid • silver nitrate solution • barium nitrate solution
• test solutions containing carbonate ions, chloride ions, bromide ions, iodide ions, sulfate ions
• unidentified solutions X and Y
Method
1
Pour about 2 cm3 of one of the test solutions into a test tube.
2
Add a few drops of nitric acid and shake gently. Look closely to see if it is fizzing – if
there is no fizzing go to step 4.
3
If there is some fizzing, add more nitric acid and wait until there is no more fizzing.
4
Divide the solution between two test tubes.
5
To one of these test tubes add a few drops of silver nitrate solution and shake gently.
6
To the other add a few drops of barium nitrate solution and shake gently.
7
Wash your test tubes thoroughly.
8
Repeat steps 1–7 with the other test solutions.
9
Repeat steps 1–7 with the solutions X and Y.
Results
Record all your results in a suitable table.
Questions
1 Compare your results with the data given on page 140 of the Student Book.
2 Which negative ions were in solutions X and Y? Explain your answer.
3 A solution did not fizz when nitric acid was added to it, but formed a cream-coloured
precipitate when silver nitrate was added to the mixture. Which negative ion was
present in the original solution?
4 Some people take Epsom salts for health reasons. This compound is soluble in water
but does not react with nitric acid. The solution formed does not form a precipitate with
silver nitrate, but a white precipitate is formed when barium nitrate solution is added.
What is the negative ion in Epsom salts?
5 Mineral waters may contain carbonate ions, chloride ions and sulfate ions. What would
you see if you carried out the test method you have used in this activity?
6 Write ionic equations for the formation of the precipitates in questions 3, 4 and 5.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_05 Analysing salts
Technician sheet
Equipment and materials
Each group will need:
test tubes (×6)
test tube rack
droppers
20 cm3 each of:
– nitric acid solution (0.1 mol dm−3)
– silver nitrate solution (0.05 mol dm−3)
– barium chloride or nitrate solution (1 mol dm−3)
about 2 cm3 each of 1 mol dm−3 solution of:
– sodium carbonate labelled ‘Solution containing carbonate ions’
– sodium chloride labelled ‘Solution containing chloride ions’
– sodium or potassium bromide labelled ‘Solution containing bromide ions’
– sodium or potassium iodide labelled ‘Solution containing iodide ions’
– sodium sulfate labelled ‘Solution containing sulfate ions’
solutions of two of the above labelled ‘Solution X’ and ‘Solution Y’
Method
Full instructions are given on practical sheet c5_05.
Notes
It is important to use clean test tubes to prevent contamination – students should wash
the test tubes carefully between tests.
It is important not to contaminate the test solutions. Dropping bottles are better than
droppers to deliver the test solutions to students.
The volumes suggested are not critical and there is no need to measure volumes. 2 cm3
is about a 2 cm depth in a test tube.
The experiment can be done on a smaller scale using dimple trays. Two samples of
each test solution are needed – nitric acid is added to both; then silver ions to one and
barium ions to the other.
As an additional point of interest, the effect of light on the silver salts (particularly silver
chloride) can be noted.
The expected results are given in Appendix G of the specification and Student Book
p.140.
Health and Safety
Nitric acid is CORROSIVE – wear goggles.
Silver nitrate is corrosive but is an IRRITANT at the concentration used here.
Barium salts are toxic by ingestion but are low hazard at the concentration used here.
If a member of CLEAPSS, refer to Hazcards 10A, 11 and 87.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_06 Minerals and giant molecules
Resources
Student Book pages 144−145 Interactive Book: iCould career video ‘How coal, oil and natural gas were formed’ Homework
pack c5_06
Files on Teacher Pack CD: c5_06_worksheet
Samples of quartz, graphite and (optional) diamond
Learning outcomes
C5.3.1 recall that the Earth’s lithosphere (the rigid outer layer of the Earth made up of the crust and the part of
the mantle just below it) is made up of a mixture of minerals
C5.3.2 recall that diamond and graphite are minerals, both of which are composed of carbon atoms
C5.3.3 explain the properties of diamond in terms of a giant structure of atoms held together by strong covalent
bonding (for example, melting point, boiling point, hardness, solubility and electrical conductivity)
C5.3.4 understand how the giant structure of graphite differs from that of diamond, and how this affects its
properties
C5.3.5 recall that silicon, oxygen and aluminium are very abundant elements in the Earth’s crust
C5.3.6 interpret data about the abundances of elements in rocks
C5.3.7 recall that much of the silicon and oxygen is present in the Earth’s crust as the compound silicon dioxide
C5.3.8 understand that silicon dioxide is another giant covalent compound and so has properties similar to
diamond
Ideas about Science
IaS 3.1 scientific hypotheses, explanations and theories are not simply summaries of the available data – they are
based on data but are distinct from them
IaS 3.2 an explanation cannot simply be deduced from data, but has to be thought up creatively to account for the
data
Literacy focus: Describing properties and explaining structures.
Numeracy focus: Extracting information from charts, graphs and tables, including abundance of elements on Earth.
ICT focus: Modelling molecules and giant structures to explain properties; using modelling software to show the
shapes of molecules and to illustrate giant structures.
In this lesson students are learning to:
recall which elements are commonly found in minerals in the Earth’s crust
explain the properties of some elements and compounds that have giant covalent structures
explain the differences in structure and properties of diamond and graphite.
Key vocabulary
mineral lithosphere giant covalent structure
Obstacles to learning
It can be difficult to visualise the three-dimensional structure of giant molecules from diagrams.
Stimuli and starter suggestions
Hand out or display samples of quartz (or diamond!). Ask students to discuss how they could show whether the
substance is a simple molecular substance or ionic compound or something else. Provide data if requested, e.g.
melting and boiling points, conductivity. Assess students’ use of ideas from the previous lessons.
Learning activities
worksheet c5_06
Low demand Show a picture of the lithosphere (Student Book p.144). Discuss the terms ‘lithosphere’, ‘crust’,
‘mantle’, ‘mineral’. Note that quartz (silicon dioxide) is a mineral, as are diamond and graphite (and so are calcium
carbonate/calcite, iron ore/haematite, rock salt, etc.) Remind students that everything is made from elements and
display the list of abundances of elements (Student Book p.144). Discuss what the figures show – e.g. almost half
the crust is oxygen, carbon is not a very common element in the crust., top two are non-metals, next seven are
metals, etc. The worksheet gives further tasks using these figures.
Teaching and learning notes: Students are expected to recall the names of the most abundant elements. Make
sure they do not get confused with the elements in the air.
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c5_06 Minerals and giant molecules continued
Standard demand Following the discussion about minerals, the lithosphere and the abundance of elements,
return to the starter topic – ‘What type of substance is quartz/ diamond?’. Confirm that they are not simple
molecular or ionic. Explain the structure of diamond and silicon dioxide as examples of giant covalent structures
using models and diagrams. Note that the substances have very high melting and boiling points and are nonconductors. They are also very hard and strong, and insoluble in water. As a diversion you could show a video clip
proving that diamond is form of carbon by burning it. Remind students that a covalent bond between two atoms
involves a shared pair of electrons. These bonds hold the atoms in a rigid structure. Note again the importance of
imagination and creativity in explaining giant covalent structures. There are further tasks on the worksheet that can
be done individually or as group activities.
Teaching and learning notes: If students can experience putting together part of a model of diamond they will
have a better chance of remembering the structure.
High demand Hand out samples of graphite (soft pencil leads or graphite electrodes will do) and discuss the
differences in properties to diamond. Students could carry out their own research into the similarities and
differences in the properties and structures of diamond and graphite. Alternatively show models and pictures of the
graphite structure and note the similarities (giant covalent structure) and differences (graphite has a layered lattice
of hexagonal sheets). Explain the conductivity of graphite as being due to the one ‘spare’ electron on each atom.
There is no need to refer to van der Waals’ forces or the similarity to metallic bonding.
Plenary suggestions
Ask students to name examples of each of the types of structure covered in the first half of this module. There
could be two teams – one team naming a substance and the other naming the bonding type, and vice versa.
Student Book answers
Q1 Diamond; graphite; quartz;
Q2 75%
Q3 Giant covalent structures have many millions/billions of atoms linked by covalent bonds; simple molecules have
a small number of atoms joined together.
Q4 Has a giant structure in which silicon and oxygen atoms are linked by strong covalent bonds.
Q5 Appearance – diamond clear, graphite opaque; hardness – diamond hard, graphite soft /slippery; conductivity –
diamond non-conductor, graphite conductor.
Worksheet answers
Activity 1 (Low demand)
Q1 b) oxygen; c) aluminium; d) silicon and oxygen
Q2 a) Rocks are mixtures of minerals.
b) Some minerals are elements such as diamond; or Most minerals are compounds such as quartz.
c) Non-metallic elements make up most of the minerals in the Earth’s crust.
d) The lithosphere is the part of the Earth made up of the crust and the upper mantle.
Activity 2 (Standard demand)
Q1 A – diamond; giant covalent; high melting and boiling point, non-conductor
B – carbon monoxide; simple molecular; low melting and boiling point, non-conductor
C – sodium carbonate; ionic; high melting point, conductor when liquid
Q2 Diamond and quartz have high melting and boiling points because there are many strong covalent bonds which
must be broken to make the atoms free.
Diamond and quartz are non-conductors of electricity because there are no charged particles in most giant
covalent structures.
Diamond and quartz have similar shaped crystals because both silicon and carbon atoms can form four
covalent bonds.
Diamond and quartz are insoluble in water because water molecules are not strongly attracted to the particles
that make up giant covalent structures.
Activity 3 (High demand)
Q1 a) Both have many strong covalent bonds.
b) Diamond – all atoms linked by strong covalent bonds; graphite – atoms bonded in separate layers.
c) Diamond – no free charged particles; graphite has free electrons between the layers.
d) Diamond – each carbon atom has four bonds, tetrahedral; Graphite – three bonds per atom,
trigonal/hexagonal shape.
Q2 a) Diamond; it is very hard
b) Graphite; good conductor and slippery
c) Graphite; high melting point (not as expensive as diamond)
d) Diamond; very hardwearing
e) Graphite; layers slippery
f) Diamond; transparent/sparkly
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_06 Minerals and giant molecules
1
1
Minerals and the lithosphere
The table shows the most common elements in the Earth’s crust.
Element
Percentage in the
Earth’s crust
Oxygen
47
Silicon
28
Aluminium
8
Iron
5
The rest
12
a) Put the data about the abundance of the elements into a pie chart.
b) Which element makes up almost half of the Earth’s crust? ......................................
c) Which is the most abundant metal in the Earth’s crust? ..........................................
d) Quartz is possibly the most abundant mineral in the Earth’s crust. Which two
elements form quartz?
................................................................................................................................
2
There is something wrong in each of the following statements. Rewrite each sentence
with the mistake corrected.
a) Minerals are mixtures of rocks.
................................................................................................................................
b) Some minerals are compounds such as diamond.
................................................................................................................................
c) Metallic elements make up most of the minerals in the Earth’s crust.
................................................................................................................................
d) The lithosphere is the part of the Earth made up of the crust..
................................................................................................................................
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c5_06 Minerals and giant molecules continued
2
1
Giant covalent structures
The table below shows three substances that contain carbon.
Substance
Melting point
Boiling point
Electrical conductivity
A
3550
4827
Non-conductor
B
−199
−191
Non-conductor
C
851
Decomposes
Conducts in liquid state and in solution
The substances are sodium carbonate, carbon monoxide and diamond.
a) Decide which of the substances is A, which is B and which is C.
b) State the type of bonding and structure each has and give the reasons for your
choice.
2
3
1
Match up each property with the phrase that explains it. Write out the complete
sentence linking the two parts with ‘because’.
Diamond and quartz have high
melting and boiling points...
...water molecules are not strongly
attracted to the particles that make up
giant covalent structures.
Diamond and quartz are nonconductors of electricity...
... there are many strong covalent
bonds which must be broken to make
the atoms free.
Diamond and quartz have
similar shaped crystals...
...there are no charged particles in
most giant covalent structures.
Diamond and quartz are
insoluble in water...
.. silicon and carbon atoms can both
form four covalent bonds.
Diamond and graphite
Explain the following facts about diamond and graphite.
a) Diamond and graphite have very high melting and boiling points.
b) Diamond is the hardest naturally occurring substance, but graphite is soft and
slippery.
c) Diamond is a non-conductor of electricity, but graphite conducts in the solid state.
d) Both diamond and graphite are forms of carbon, but have very different shaped
crystals.
2
Identify which form of carbon is used for the following purposes and give reasons for
your choice:
a) The cutting edge of drill bits.
b) Electrical contacts in motors.
c) Making crucibles for melting metals.
d) Making bearings that resist wear when hold moving parts in watches.
e) As a lubricant in high-temperature engines.
f)
Setting gemstones in jewellery.
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_07 Extracting metals
Resources
Student Book pages 146−147 Interactive Book: Matching pairs ‘Ores’ Homework pack c5_07
Files on Teacher Pack CD: c5_07_practical; c5_07_technician
Samples of minerals of various metals, particularly iron, copper and zinc; equipment for practical
Learning outcomes
C5.4.1 recall that ores are rocks that contain varying amounts of minerals from which metals can be extracted
C5.4.2 understand that for some minerals, large amounts of ore need to be mined to recover small percentages of
valuable minerals (for example, in copper mining)
C5.4.3 recall that zinc, iron and copper are metals that can be extracted by heating the oxide with carbon, and
write simple word equations for these reactions (technical details not required)
C5.4.4 understand that when a metal oxide loses oxygen it is reduced, while the carbon gains oxygen and is
oxidised
Literacy focus: Using the terms to describe redox reactions.
Numeracy focus: Calculating the percentage of metal in ores.
ICT focus: Viewing video clips showing metals being extracted on a large scale.
In this lesson students are learning to:
explain why large amounts of ore are mined to extract metals
describe the reactions used to extract metals from their ores
explain oxidation and reduction reactions.
Key vocabulary
ore reduce reduction oxidise oxidation redox reaction
Obstacles to learning
There is a high chance of failure in the experiment, and students may have difficulty in seeing how the small scale
and unsuccessful reaction is scaled up to produce millions of tons of metal a year. The term ‘reduction’ has rather
obscure origins and can be difficult for students to relate to reactions.
Stimuli and starter suggestions
Hand out or display samples of minerals of various metals but particularly iron, copper and zinc. Students should
record their appearance and discuss how they are obtained from the ground – forms of mining (deep, opencast)
separation from waste rock – and the effect on the environment.
Learning activities
practical c5_07
Low demand Remind students that the lithosphere is made up of minerals containing many different elements,
many of them metals combined in ionic compounds. Explain the term ‘ore’ and also that a metal often makes up
only a small fraction of the ore. Explain that most metal minerals are compounds of the metal and oxygen (or other
elements) and that the compound must be broken down to get the metal. Students may recall from earlier work that
carbon can do this. Explain the term ‘reduction’.
Introduce the class experiment (see the practical sheet). Make sure that students see that carbon can remove the
oxygen from copper oxide leaving copper. There are further questions and tasks on the practical sheet; make sure
that students can write word equations for the process with copper, and also with iron and zinc.
Teaching and learning notes: The term ‘ore’ is often misused – make sure it is defined correctly. Note that no
copper ore is made up of copper(II) oxide but students are not required to know the reactions that convert copper
ores to copper(II) oxide prior to reduction. Indeed, little copper is produced by reduction of copper oxide and the
actual reactions are much more complex than dealt with here. Similarly little zinc is now produced by the smelting
reaction.
Standard demand Either before or after carrying out the class experiment discuss the concept of an economical
ore. Note that iron is much more common than copper and that the latter commands a much higher price, so very
low percentage copper ores are viable while iron ores must have (at present) much higher percentages. Students
could investigate the price of metals on the internet and news items about shortages of metals (and theft of
valuable metals such as copper).
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c5_07 Extracting metals continued
Teaching and learning notes: While the focus of the lesson is the reduction of metal ores with carbon, it is
worthwhile keeping in student’s minds the uses of various metals and their place in society. This includes the rarer
metals that have such a great importance in modern electronic applications. We will meet this again in c5_12.
High demand Explain the terms ‘oxidation’ and ‘reduction’ as the gain and loss of oxygen, respectively. Ask
students to interpret equations for the extraction of metals in terms of oxidation and reduction. There are further
questions on the practical sheet. Note that the extraction of metals involves other redox reactions that cannot be
explained by the ‘oxygen definition’ of redox – the electron view of redox is not covered in this module.
Plenary suggestions
Show pictures of opencast metal ore mines and ask students to discuss their reaction. Are the mines and the
environmental damage justified? How much do we need metals (not just iron, copper and zinc)? Are there
alternatives to metals or to making big holes in the ground? This could be done in the form of a short debate or
groups could be given different questions to discuss and report back on.
Student Book answers
Q1 A rock that contains a mineral from which a metal can be obtained.
Q2 Copper oxide + carbon → copper + carbon dioxide
Q3 There is a much higher percentage of iron in the Earth’s crust than copper.
Q4 10 kg
Q5 Carbon is oxidised; iron oxide is reduced.
Q6 No; if a substance loses oxygen then another substance must have gained oxygen.
Practical sheet answers
Q1 A colour change; from all black to small red bits.
Q2 Copper is the only red metal.
Q3 Carbon dioxide
Q4 Copper oxide + carbon → copper + carbon dioxide
Q5 It lost oxygen.
Q6 Both reduction and oxidation take place.
Q7 a) Mineral – a solid element or compound found in rocks; ore – a rock containing a mineral from which a metal
can be extracted (economically).
Q8 a) Gas
b) Carbon; it gains oxygen.
c) Zinc oxide; it loses oxygen.
6
9
Q9 (16 × 10 ) ÷ (6 × 10 ) × 100 = 0.27%
Q10 2CuO(s) + C(s) → 2Cu(s) + CO2(g)
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c5_07 Extracting metals
P
Reducing copper oxide
Objectives
In this activity you will:
observe the reduction of copper oxide
learn that certain metals can be extracted from their ores by a redox reaction with
carbon.
Copper oxide is HARMFUL and can harm the environment. Avoid contact with the
powder and dispose of it as instructed at the end of the experiment.
The apparatus will get hot during the experiment – do not attempt to pick up the
crucible or the tripod until you are sure it has cooled sufficiently.
Equipment and materials
• Bunsen burner, tripod • pipe-clay triangle • crucible and lid • bench mat
• spatula • copper oxide powder • charcoal powder
Method
1
Put one spatula of copper oxide powder in the crucible. Add one spatula of
charcoal powder and mix the two together. Sprinkle another spatula of charcoal
powder over the mixture. Put the lid on the crucible.
2
Put the crucible with its lid on a pipe-clay triangle on a tripod. Make sure that the
crucible cannot fall through the triangle. Put the Bunsen burner under the crucible.
3
Light the Bunsen burner and heat the crucible strongly for five minutes.
4
Turn the Bunsen burner off and allow the apparatus to cool. Do not lift the lid of the
crucible until it is cool enough to hold the crucible in your hands. It is important to
be patient at this stage – opening the crucible too soon could affect the
results of the experiment.
5
Empty the contents of the cool crucible onto the bench mat.
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C5_07 Extracting metals continued
Results
Record the appearance of the reactants and of the mixture after it has cooled.
Questions
1
What are the signs that a reaction has taken place?
2
How were you able to identify one of the products of the reaction?
3
What other, invisible, product was there?
4
Write a word equation for the reaction.
5
Why do we say that the copper oxide was reduced in this reaction?
6
Why is this reaction called a redox reaction?
7
Iron oxide is found as the mineral, haematite, in iron ore.
a) What is meant by the terms ‘mineral’ and ‘ore’?
b) Iron was first extracted from its ore using charcoal. Then in the 18th century
coke began to be used.
Find out more about the development of the iron extraction industry. Write a
brief magazine article or design a PowerPoint display.
8
In the extraction of zinc from its ore, a mixture of zinc oxide and carbon is heated to
over 1000 °C. The equation for the reaction is:
2ZnO(s) + C(s) → 2Zn(g) + CO2(g)
a) What state are the products?
b) Which reactant is oxidised? Explain your answer.
c) Which reactant is reduced? Explain your answer.
Extension
9
16 million tons of copper have been obtained from 6 billion tons of rock at the
largest mine in the world. What was the percentage of copper in the rock?
(Higher tier only)
10 Write a balanced chemical equation for the extraction of copper (Cu) from copper
oxide (CuO) using carbon (C).
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c5_07 Extracting metals
Technician sheet
Equipment and materials
Each group will need:
crucible and lid
Bunsen burner
tripod and pipe-clay triangle
spatula
copper(II) oxide powder
charcoal powder
For demonstration (optional):
metal ores
minerals containing metals – particularly of iron, copper, and zinc.
Method
Full instructions are given on practical sheet c5_07.
Notes
Very little of the copper oxide is reduced at the temperature of a Bunsen flame, but if
students are patient and let the crucible cool before opening the lid they should see
patches or specks of red. These are evidence that reduction has occurred but are likely
to be copper(I) oxide as well as copper.
The experiment can be done in small borosilicate test tubes (ignition tubes), but trapped
air and gases evolved during the heating tend to blow the powders out of the tube, so it
is not recommended.
Collect the mixtures at the end of the experiment – they can be used again as premixed reactants or separated by reaction with sulfuric acid.
Health and Safety
Copper(II) oxide is HARMFUL and an ENVIRONMENTAL POLLUTANT. Avoid contact
with skin and collect the residues at the end of the lesson. Goggles should be worn.
Warn students that the apparatus will get very hot and remain hot for some time after
heating stops.
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c5_08 Chemistry in shorthand
Resources
Student Book pages 148−149 Interactive Book: Practical investigations ‘Salts’ Homework pack c5_08
Files on Teacher Pack CD: c5_08_worksheet
Molecular models or counters to represent atoms
Learning outcomes
C5.4.6 write word equations when given appropriate information
C5.4.7 interpret symbol equations, including the number of atoms of each element, the number of molecules of
each element or covalent compound and the number of ‘formulas’ of ionic compounds, in reactants and products
[In this context, ‘formula’ is used in the case of ionic compounds as an equivalent to molecules in covalent
compounds; the concept of the mole is not covered in the specification]
C5.4.8 balance unbalanced symbol equations
C5.4.9 write balanced equations, including the state symbols (s), (l), (g) and (aq), when given appropriate
information
C5.4.10 recall the state symbols (s), (l), (g), and (aq) and understand their use in equations
Literacy focus: Describing reactions and writing word equations.
Numeracy focus: Balancing equations (Higher tier).
In this lesson students are learning to:
write word equations for chemical reactions
understand balanced symbol equations for chemical reactions.
Obstacles to learning
Some students find chemical equations too abstract. Demonstrating reactions and using models can make the
topic more concrete.
Notes
This lesson can be used in one of three ways:
to help students understand the purpose of writing chemical equations and help them learn how to write
balanced equations
to reinforce understanding of chemical equations if they have been introduced in earlier modules (C4) prior to the
next topic on chemical calculations
as a pause to summarise and reinforce the topics covered earlier in this module.
Alternatively the lesson can be skipped.
Stimuli and starter suggestions
Display an equation for a simple chemical reaction using Dalton’s and Berzelius’ symbols (see Student Book
p.148 for Dalton’s symbols) – e.g. C + O2 → CO2 or 2H2 + O2 → 2H2O. Ask students to discuss what the
equations show and why Dalton’s symbols have been forgotten and why we use what is basically Berzelius’
system (Berzelius’ was easier to print).
Learning activities
worksheet c5_08
Low demand Read out a description of a reaction that students may have observed during this module (see
Student Book p.149 for a couple of examples). Ask them to pick out the reactants and products and either give the
word equation or ask them to write it. Ask students to suggest why we write word equations (shorter than the
description). The worksheet gives further examples and other summary exercises.
Teaching and learning notes: Examples from the current module are given, but reactions that students have
experienced in previous modules can also be used.
Standard demand Explain that formulae show the number of atoms joined together to form molecules, where the
bonding is covalent, or ‘formula units’ in ionic compounds (more accurately it is the ratio of the number of atoms in
the latter). Display a balanced chemical equation and ask students to discuss or make a list of all the jobs that it
does – describes the reaction, is ‘shorthand’ for the reaction, shows what reactants are needed to give particular
products, how many atoms, molecules and ‘formula units’ are involved in the reaction, the states of the reactants
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C4_08 Chemistry in shorthand continued
and products. Show how the number of atoms of each element is the same on both sides of the equation, and
explain the meaning of the other symbols: ‘+’ on the left means ‘reacts with’ while the ‘+’ on the right means ‘and’;
‘→’ means ‘goes to’ or ‘react to form’. Emphasise the difference between the large numbers before formulae and
the subscript numbers within the formulae. There are further equations for students to interpret on the worksheet
along with other summary exercises.
Teaching and learning notes: Unless students are taking the Higher tier exam they do not need to be able to
write or balance chemical equations themselves.
High demand Remind students of the use of charges on ions in writing the formulae of ionic compounds (c5_03)
and go through the steps in writing balanced chemical equations. (Note this is also covered in c4_07.) Use
molecular models or counters to represent atoms in equations. A pair of scales could be used to show that the two
sides of the equation balance. Note the patterns in the equations for reactions involving Group 1 metals or ions with
2+ charges. Also reinforce the writing of ionic equations for precipitation reactions (c5_04). There are further
examples to try and summary questions on the worksheet.
Plenary suggestions
Depending on the abilities of the students, give them a word equation and ask them to say what is happening in the
reaction, a balanced chemical equation to describe or an incomplete equation to finish and balance.
Student Book answers
Q1 Reactants – copper oxide solid, carbon solid; Products – copper solid, carbon dioxide gas
Q2 Copper sulfate solution + sodium hydroxide solution → copper hydroxide solid + sodium sulfate solution
Q3 a) A molecule of carbon dioxide; b) 1; c) Cu 2, C 3, O 6; d) Gas
Q4 2CuO(s) + C(s) → 2Cu(s) + CO2(g)
Q5 CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)
Worksheet answers
Activity 1 (Low demand)
Q1 a) Hydrogen + oxygen → water
b) Potassium carbonate + nitric acid → potassium nitrate + water + carbon dioxide
c) Zinc sulfate + sodium hydroxide → zinc hydroxide + sodium sulfate
d) Barium chloride + sodium sulfate → barium sulfate + sodium chloride
Q2 Atmosphere – argon, nitrogen; Hydrosphere – water, sodium chloride, potassium bromide;
Lithosphere – diamond, quartz, iron ore, zinc oxide
Activity 2 (Standard demand)
Q1 a) Carbon, C, 1; oxygen, O, 2
b) Calcium, Ca,1; chlorine, Cl, 2; sodium, Na, 2; oxygen, O, 2; hydrogen, H, 1
c) Sodium, Na, 1; chlorine, Cl, 1; Silver, Ag, 1; nitrogen, N, 1; oxygen, O, 3
d) Potassium, K, 2; sulfur, S, 1; oxygen, O, 4; barium, Ba, 1; chlorine, Cl, 2
e) Iron, Fe, 4; oxygen, O, 6; carbon, C, 3
Q2 Simple molecular – often gases at room temperature; non-conductor of electricity; bonds formed by pairs of
electrons shared between atoms.
Giant covalent – have a crystal lattice structure of many particles; bonds formed by pairs of electrons shared
between atoms; non-conductor of electricity; high melting point.
Giant ionic – atoms gain or lose electrons to form ions; made up of charged particles called ions; have a crystal
lattice structure of many particles; oppositely charged ions attract each other; high melting point; often soluble
in water; conducts electricity in the liquid state.
Activity 3 (High demand)
Q1 a) N2(g) + O2(g) → 2NO(g)
b) MgCO3(s) + 2HNO3(aq) → Mg(NO3)2(aq) + H2O (l) + CO2(g)
c) Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq)
3+
–
d) Fe (aq) + 3OH (aq) → Fe(OH)3(s)
e) 2FeO(s) + C(s) → 2Fe(l) + CO2(g)
Q2 a) 2H2(g) + O2(g) → 2H2O(l)
b) K2CO3(aq) + 2HNO3(aq) → 2KNO3(aq) + H2O(l) + CO2(g)
c) ZnSO4(aq) + 2NaOH(aq) → Zn(OH)2(s) + Na2SO4(aq)
d) BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
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c5_08 Chemistry in shorthand
1
1
Word equations and the Earth
Read the descriptions of reactions that follow. Draw up a table of reactants and
products for each reaction and write a word equation.
a) Molecules of hydrogen gas react with molecules of oxygen to form molecules of
water.
......................................................................................................................................
b) A solution of potassium carbonate reacts with nitric acid to make potassium nitrate
solution, water and carbon dioxide gas.
................................................................................................................................
c) Zinc sulfate solution reacts with sodium hydroxide solution to form a precipitate of
zinc hydroxide and sodium sulfate solution.
................................................................................................................................
d) When barium chloride solution was added to sodium sulfate solution a white
precipitate of barium sulfate formed and sodium chloride solution.
................................................................................................................................
2
The surface of the Earth is made up of the atmosphere, the hydrosphere and the
lithosphere. Make a table with these parts of the Earth’s surface as headings. Put each
of the following substances in the part of the Earth it is most likely to be found.
Diamond
Iron ore
Nitrogen gas
Argon gas
Sodium chloride
Water
Quartz
Zinc oxide
Potassium bromide
Atmosphere
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Lithosphere
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c5_08 Chemistry in shorthand continued
2
1
Equations and bonds
Copy the table and headings shown below:
Element name Symbol Number of atoms involved
in the equation
Complete the table for each of the balanced chemical equations that follow:
a) C(s) + O2(g) → CO2(g)
b) CaCl2(aq) + 2NaOH(aq) → Ca(OH)2(s) + 2NaCl(aq)
c) NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
d) K2SO4(aq) + BaCl2(aq) → 2KCl(aq) + BaSO4(s)
e) 2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)
2
Match the boxed statements to the type of substance:
simple molecular
giant covalent
giant ionic
Note that some of the statements apply to more than one type of substance.
Conducts electricity
in the liquid state
Have a crystal lattice
structure of many particles
Oppositely charged
ions attract each other
3
Made up of charged
particles called ions
Often soluble
in water
Often gases at
room temperature
High melting
point
Bonds formed by pairs of
electrons shared between atoms
Non-conductor
of electricity
Atoms gain or lose
electrons to form ions
Draw a large mind map with ‘Structures of Materials’ at the centre. Make sure you
include the following terms:
simple molecular
giant covalent
ionic
covalent bond
ionic bond
molecule
ion
lattice
electron pairs
positive
negative
melting point
boiling point
electrical conduction
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c5_08 Chemistry in shorthand continued
3
1
2
Ions and molecules
Balance the following symbol equations – the numbers 1, 2 or 3 fit in the gaps.
a)
... N2(g) + ... O2(g) → ... NO(g)
b)
... MgCO3(s) + ... HNO3(aq) → ... Mg(NO3)2(aq) + ... H2O(l) + ... CO2(g)
c)
... Pb(NO3)2(aq) + ... NaI(aq) → ... PbI2(s) + ... NaNO3(aq)
d)
... Fe3+(aq) + ... OH−(aq) → ... Fe(OH)3(s)
e)
... FeO(s) + ... C(s) → ... Fe(l) + ... CO2(g)
Read the following descriptions of reactions.
Write balanced chemical equations for each
reaction (the formula of nitric acid is HNO3).
Positive ions
a) Molecules of hydrogen gas react with
molecules of oxygen to form molecules of
water.
Potassium, K
b) A solution of potassium carbonate reacts
with nitric acid to make potassium nitrate
solution, water and carbon dioxide gas.
Barium, Ba
+
−
Sodium, Na
Chloride, Cl
+
2+
Negative ions
Hydroxide, OH
−
2−
Zinc, Zn
Sulfate, SO4
2+
2−
Carbonate, CO3
c) Zinc sulfate solution reacts with sodium hydroxide solution to form a precipitate of
zinc hydroxide and sodium sulfate solution.
d) When barium chloride solution was added to sodium sulfate solution a white
precipitate of barium sulfate formed and sodium chloride solution.
3
Look over all the equations that you have written in this module so far. Make sure you
understand the reactions they explain and that they are balanced and have state
symbols.
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c5_09 Atomic masses
Resources
Student Book pages 150−151 Homework pack c5_09
Files on Teacher Pack CD: c5_09_worksheet; c5_09_practical; c5_09_technician
Plasticine; equipment for practical
Learning outcomes
C5.4.11 use the Periodic Table to obtain the relative atomic masses of elements
C5.4.12 use relative atomic masses to calculate relative formula masses
C5.4.13 calculate the mass of an element in the gram formula mass of a compound
C5.4.14 calculate the mass of the metal that can be extracted from a mineral given its formula or an
equation
Numeracy focus: Calculating relative formula masses; carrying out calculations to find the percentage of an
element in a compound and the mass of an element that can be obtained from its compound.
ICT focus: Using a spreadsheet to calculate relative formula mass.
In this lesson students are learning to:
use relative atomic masses to calculate relative formula mass of a compound
work out how much of the mass of a compound is made up by each element.
Key vocabulary
relative atomic mass relative formula mass gram formula mass
Obstacles to learning
The terms such as ‘relative atomic mass’ can themselves make this topic seem more difficult than it really is. Try to
build up confidence with numbers by giving lots of simple examples.
Stimuli and starter suggestions
Ask students to consider how we measure the mass of objects and to suggest a design for very small objects.
(They could try using splints and Plasticine to compare the mass of grains of rice.) Assess students’ appreciation
that all balances actually compare the mass of something with something else. Note that scientists have
developed a balance that can measure individual atoms (Student Book p.150).
Learning activities
worksheet c5_09 + practical c5_09
Low demand Display a Periodic Table and remind students that each element has atoms with a particular mass.
Explain that relative atomic mass (RAM) compares the mass of one atom with another – the standard used is
carbon. Show, perhaps using Plasticine models, that a magnesium atom has the mass of two carbon atoms, and
hence has a RAM of 24. There are four other elements with RAMs that are an approximate multiple of 12: Ti (48),
Kr (84), Mo (96), Ag (108). Use these to reinforce the relationship of carbon-12 and RAM. Ask students to look up
the RAMs of named elements from the Periodic Table. There are further questions in activity 1 on the worksheet.
The importance of mass in chemical reactions can be appreciated by doing the class experiment described on the
practical sheet. All students should answer questions 1–3.
Teaching and learning notes: Help students to find elements in the Periodic Table by name and symbol.
Standard demand Explain that for compounds and for molecules of elements, we can compare the mass of a
molecule (or ‘formula unit’) to carbon-12. Explain that a relative formula mass (RFM) can be calculated by adding
up the RAMs of the atoms in the formula – activity 2 on the worksheet gives practice in this. Explain the term ‘gram
formula mass’ (GFM) and show how to calculate the mass and percentage mass of an element in a compound.
Make sure students put in the units for GFM. The worksheet gives further questions on this.
The practical activity allows students to compare experimental data with the value predicted by calculation for the
amount of copper oxide in copper carbonate (questions 4–9).
Students could design a spreadsheet for calculating the RFM of compounds – summing the RAMs in a compound
with formula MxNy.
Teaching and learning notes: Note that the concepts of isotopes and the mole are not required by this
specification.
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c5_09 Atomic masses continued
High demand Build on the ideas developed above to consider the predicted amount of a metal that can be
extracted from any mass of a compound given the formula or the equation for the reaction. Student Book p. 151
gives some examples on this and activity 3 on the worksheet provides further practice questions. Higher tier
students should also attempt question 10 on the practical sheet.
Plenary suggestions
Depending on the ability of the students, ask quick-fire questions on the lines of question 2 in activity 1 on the
worksheet, or display the formulae of compounds and ask for the RFM or GFM. Alternatively give teams a list of
formulas and a time limit to calculate the RFMs.
Student Book answers
Q1 84
Q2 a) 20; b) 27; c) 39; d) 63.5
Q3 MgO = 40; CaCl2 = 111; CO2 = 44; CuSO4 = 159.5
Q4 66.5 g
Q5 65 g
Worksheet answers
Activity 1 (Low demand)
Q1 a) 48; b) 4; c) 9
Q2 a) (i) 28; (ii) 7; (iii) 56; (iv) 80
b) (i) oxygen; (ii) sodium; (iii) chlorine; (iv) gold
c) (i) manganese (55); (ii) bromine (80; (iii) iron (56)
Activity 2 (Standard demand)
Q1 a) (i) 2; (ii) 32; (iii) 160
b) (i) 64; (ii) 28; (iii) 16
c) (i) 58.5; (ii) 100; (iii) 170
Q2 a) 79.5 g; b) 63.5 g; c) 80%
Activity 3 (High demand)
Q1 a) 97 g; b) 65 g; c) 67%; d) 67 g
Q2 127 tonnes
Practical sheet answers
Q1 Experimental result (reading 2 − reading 1)
Q2 Experimental result (reading 6 – reading 1)
Q3 No further change in colour from green to black.
Q4 Experimental result (answer Q2 ÷ answer Q1 × 100%)
Q5 To ensure that there was no further loss of mass; and so all the copper carbonate has reacted.
Q6 CuCO3 = 123.5; CuO = 79.5
Q7 123.5 g; 79.5 g
Q8 79.5 ÷ 123.5 × 100 = 64.4%
Q9 b) Sources of error include loss of copper carbonate or copper oxide by spillage or by being blown out of the
boiling tube; failure to complete the reaction; damp or dirty tube; inaccurate weighing (failure to zero balance or
misreading the data).
Q10 6.44 tonnes
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_09 Measuring mass
P
How much copper oxide is there in copper carbonate?
Objectives
In this activity you will:
measure the mass of reactants and product of a reaction
compare experimental data with values predicted by theory.
Copper carbonate, CuCO3, is found naturally as the mineral malachite – it is often in rocks
used as copper ore. The copper carbonate is heated to drive off carbon dioxide gas to
leave copper oxide from which copper can be extracted:
copper carbonate → copper oxide + carbon dioxide
CuCO3(s) → CuO(s) + CO2(g)
Copper carbonate is harmful – avoid inhaling the powder.
Glass tubes may shatter when heated – wear goggles at all times.
Do not try to pick up glass tubes that have been heated.
Equipment and materials
• boiling tube • tongs • Bunsen burner • bench mat • spatula
• copper carbonate • access to a balance
Method
1 Weigh a clean dry boiling tube.
2 Put a spatula full of copper carbonate in the boiling tube and weigh it again.
3 Using a pair of tongs, hold the closed end of the boiling tube in a blue Bunsen flame.
Heat it gently at first, but then more strongly until no further change takes place.
4 Allow the tube to cool and then weigh it and its contents. Make sure you do not spill any
of the powder.
5 Re-heat the tube for another 5 minutes and then allow it cool. Weigh the tube and
contents again.
6 Repeat stage 5 until the mass is constant.
7 Do not throw the powder away – return it for re-use.
Results
Record all the balance readings and observations.
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c5_09 Measuring mass continued
Questions
1
What mass of copper carbonate did you start with?
2
What mass of copper oxide did you end up with?
3
How did you know that the reaction was finished?
4
Calculate the percentage of copper oxide in copper carbonate:
% of copper oxide = mass of copper oxide formed × 100
mass of copper carbonate used
5
Why was the tube and contents re-heated in steps 5 and 6?
6
Calculate the relative formula mass of copper carbonate, CuCO3 and copper oxide,
CuO.
7
What are the gram formula masses of copper carbonate and copper oxide?
8
What percentage of the gram formula mass of copper carbonate is copper oxide?
9
Your answer to question 8 is the theoretical prediction for the experiment.
a) Would you say that you experimental result (question 4) is close or not very close?
b) What are the causes of the difference between your experimental result and the
predicted value?
Extension (Higher tier only)
10 What mass of copper oxide could be obtained from 10 tonnes of copper carbonate?
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c5_09 Measuring mass
Technician sheet
Equipment and materials
Each group will need:
borosilicate glass boiling tube
copper carbonate powder
spatula
tongs
Bunsen burner
bench mat
access to a balance reading to 0.01 g
Method
Students determine how much copper oxide can be obtained from copper carbonate. Full
instructions are given on practical sheet c5_09.
Notes
Smaller tubes can be used, but some powder may escape during heating.
Crucibles and lids can be used instead of boiling tubes.
Health and Safety
Copper carbonate is HARMFUL – avoid inhaling the powder and dispose of it carefully
(the copper oxide formed can be collected for use in other experiments).
The boiling tubes may shatter – wear goggles.
The boiling tube will get hot – make sure that students allow the tubes to cool before
attempting to carry them to the balance.
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c5_09 Atomic masses
1
1
Relative atomic mass
One titanium atom has a mass that is the same as four carbon atoms.
C
C
C
C
Ti
a) Carbon has a relative atomic mass of 12.
What is the relative atomic mass of titanium? .........................................................
Helium atoms have a mass that is one-third of a carbon atom.
What is the relative atomic mass of helium? ...........................................................
b) Beryllium atoms are three-quarters of the mass of a carbon atom.
What is the relative atomic mass of beryllium? ........................................................
2
Use a Periodic Table (see page 309 in the Student Book) to answer the following
questions.
a) Find the relative atomic masses of:
(i) silicon (Si) ..................
(ii) lithium (Li) ......................
(ii) iron (Fe) ....................
(iv) bromine (Br) ..................
b) Find the names of the elements that have these relative atomic masses:
(i) 16 ..............................
(ii) 23 ..................................
(iii) 35.5 ..........................
(iv) 197 ...............................
c) Find the elements that have a relative atomic mass that is:
(i) five times the relative atomic mass of boron (B) ....................................
(ii) twice the relative atomic mass of calcium (Ca) .....................................
(iii) half the relative atomic mass of cadmium (Cd) ....................................
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c5_09 Atomic masses continued
2
1
Relative formula mass
Use a Periodic Table (see page 309 in the Student Book) to find the relative atomic
masses you need to work out the relative formula masses of the following.
a) Simple molecular elements:
(i) hydrogen, H2
(ii) oxygen, O2
(iii) bromine, Br2
b) Simple molecular compounds:
(i) sulfur dioxide, SO2
(ii) carbon monoxide, CO
(iii) methane, CH4
c) Formula units of giant ionic compounds:
(i) sodium chloride, NaCl
(ii) calcium carbonate, CaCO3
(iii) silver nitrate, AgNO3
2
a) What is the gram formula mass of copper oxide, CuO?
b) What is the mass of copper in the gram formula mass of copper oxide?
c) What is the percentage mass of copper in the gram formula mass of copper oxide?
3
1
Reacting masses
Zinc sulfide, ZnS, is a mineral found in zinc ores.
a) What is the gram formula mass of zinc sulfide?
b) What mass of zinc is present in the gram formula mass of zinc sulfide?
c) What is the percentage of zinc in zinc sulfide?
d) If zinc sulfide makes up 10% of zinc ore, what mass of zinc could be obtained from
1 kg of zinc ore?
2
The equation for a reaction for producing copper metal from its ore is:
Cu2S(s) + O2(g) → 2Cu(l) + SO2(g)
What mass of copper could be produced by heating 159 tonnes of the copper mineral
in oxygen? Show your working.
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c5_10 Using electrolysis
Resources
Student Book pages 152−153 Homework pack c5_10
Files on Teacher Pack CD: c5_10_worksheet; c4_11_technician
Equipment for demonstration; video clips and animations of electrolysis, particularly in the extraction of aluminium
Learning outcomes
C5.4.5 understand that some metals are so reactive that their oxides cannot be reduced by carbon
C5.4.15 describe electrolysis as the decomposition of an electrolyte with an electric current
C5.4.16 understand that electrolytes include molten ionic compounds
C5.4.17 describe what happens to the ions when an ionic crystal melts
C5.4.18 understand that, during electrolysis, metals form at the negative electrode and non-metals form at the
positive electrode
C5.4.19 describe the extraction of aluminium from aluminium oxide by electrolysis
C5.4.20 understand that during electrolysis of molten aluminium oxide, positively charged aluminium ions
gain electrons from the negative electrode to become neutral atoms
C5.4.21 understand that during electrolysis of molten aluminium oxide, negatively charged oxide ions lose
electrons to the positive electrode to become neutral atoms which then combine to form oxygen molecules
C5.4.22 use ionic theory to explain the changes taking place during the electrolysis of a molten salt (limited
to using diagrams or symbol equations to account for the conductivity of the molten salt and the changes
at the electrodes)
Literacy focus: Using the terms associated with electrolysis.
Numeracy focus: Balancing ionic equations.
ICT focus: Viewing video clips to show aluminium being extracted on a large scale; animations to illustrate the
ionic theory of electrolysis.
In this lesson students are learning to:
explain why reactive metals must be extracted from their oxides by electrolysis
describe and explain what happens during the electrolysis of molten electrolytes.
Key vocabulary
electrolysis electrolyte decompose electrode cathode anode
Obstacles to learning
The ionic theory of electrolysis requires visualisation of an abstract concept. This is difficult for many students who
may nevertheless be able to learn the definitions and identify the products in the reactions
Stimuli and starter suggestions
Ask students to list objects made from aluminium (e.g. cans, pans, kitchen foil, furniture, cars, aircraft, electric
cables, cladding and parts of buildings) and discuss its importance in modern society.
Learning activities
worksheet c5_10
Low demand Demonstrate the electrolysis of a molten salt – see technician sheet c4_11. Explain the terms
‘electrolysis’, ‘electrolyte’, ‘electrode’. Show a diagram of electrolysis and ask students to label the electrolyte and
electrodes. Point out that the electrolyte must be molten so that the particles (ions) can move by the passage of the
current. There are questions about electrolysis on worksheet c4_11 and there are questions more specifically on
the extraction of aluminium on worksheet c5_10.
Teaching and learning notes: This may topic may have been covered before in c4_11, but here it is more specific
to the electrolysis of aluminium. Students do not need to know details about the electrolyte or the reaction of
oxygen with the carbon anodes.
Standard demand Remind students about the metals that can be extracted by reaction of their oxide with
carbon. Ask for reasons why this does not work for the alkali metals, magnesium, calcium and aluminium. Possible
answers – metals too reactive/oxides too stable; carbon not reactive enough to take the oxygen away; not enough
energy given out by carbon when it combines with oxygen. Discuss alternative ways of decomposing the oxide (or
other ionic compounds), including electrolysis, and show video clips (from the internet) of the extraction of
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c5_10 Using electrolysis continued
aluminium. Discuss the reasons for the aluminium being formed at the negative electrode. Show an animation of
the process or ask students to make a storyboard or design their own animation. Remind students that the
electrolyte must be molten. Worksheets c5_10 and c4_11 provide further tasks on this topic.
Teaching and learning notes: At Foundation level students need to understand that ions lose their charge at the
electrodes to form metals and non-metals, but do not need to understand the gain or loss of electrons.
High demand Explain the ionic equations for the reactions at the electrodes. (Note that the changes are not
referred to as ‘oxidation’ or ‘reduction’ in this specification.) Show how the half equations are combined into an
overall equation in which the electrons cancel out. Students can write similar equations for the electrolysis of
sodium chloride (Student Book p.153) and other metal salts. The worksheet gives further tasks on this.
Plenary suggestions
Ask students to discuss the statement ‘although aluminium is the most abundant metal, it is more expensive to
extract than iron.’ Points for discussion – the stability and high melting point of aluminium oxide, the amount of
energy needed, the need for plentiful electricity before aluminium could be extracted on a large scale.
Student Book answers
Q1 Molten; move; electricity; decomposed; electrolysis
Q2 Aluminium; oxygen
Q3 Electrolysis; carbon cannot reduce the oxides of reactive metals.
Q4 Aluminium ions are positively charged and are attracted to the negatively charged cathode; oxide ions are
negatively charged and are attracted to the positively charged anode.
2−
−
Q5 Anode – negative ions lose electrons; O → O + 2e
3+
−
Cathode – positive ions gain electrons; Al + 3e → Al
+
−
Q6 Cathode – potassium ions gain electrons; K + e → K
−
Anode – bromide ions lose electrons; Br → Br + e
−
Worksheet answers
Activity 1 (Low demand)
Q1 As Figure 3 on Student Book p. 153, with oxygen collecting on positive electrodes
Q2 a) (Molten) sodium chloride
b) Electricity causes a chemical change.
c) Electrodes
d) The ions must be free to move.
Activity 2 (Standard demand)
Q1 Keyword: electrolyte; 1: liquid; 2: decompose; 3: electrolysis; 4: current; 5: ionic; 6: aluminium; 7: oxygen
Q2 Sodium, aluminium, calcium; they are too reactive/carbon does not release enough energy to break down their
compounds.
Q3 a) Compounds of metals and non-metals are ionic/made up of ions.
b) Ions cannot move in the solid state/ions are free to move in the liquid state.
c) Aluminium ions are positively charged and are attracted to the negatively charged electrode.
d) The aluminium oxide/electrolyte is decomposed to aluminium and oxygen.
Activity 3 (High demand)
3+
−
2−
Q1 Al + 3e → Al at cathode/ negative electrode; O
2+
Q2 a) Mg ; Cl
−
→ O + 2e at anode/positive electrode
−
b) The ions are free to move and are attracted to the oppositely charged electrodes where electrons are
transferred completing the circuit
c) Mg
2+
+ 2e- → Mg
−
−
d) 2Cl → Cl2 + 2e
e) MgCl2(l) → Mg(l) + Cl2(g)
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c5_10 Using electrolysis
1
1
Electrolysis
Aluminium is extracted from aluminium oxide by electrolysis.
Use the words below to label the diagram:
molten aluminium
electric current
molten aluminium oxide
oxygen
2
electrolyte
Oliver connected two carbon rods to an electric power supply. He dipped the rods in
molten sodium chloride. Electricity flowed in the circuit, and sodium and chlorine were
formed.
a) What is the electrolyte in this experiment? .................................................................
b) Why is this an example of electrolysis? ......................................................................
....................................................................................................................................
c) What word is used for the carbon rods? ....................................................................
d) Why must the sodium chloride be molten? ................................................................
....................................................................................................................................
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c5_10 Using electrolysis continued
2
1
Extracting metals
Solve the clues to fill in the keyword puzzle.
E
1
E
2
3
4
5
6
Y
T
7
Down (keyword)
A liquid that is broken down when an electric current passes through it
Across
1 A molten compound is in this state
2 A word that means ‘to break down a compound into its elements’
3 The process of passing an electric current through a substance that breaks it down to its
elements
4 An electric ..................... flows around the circuit
5 The type of compound that conducts electricity when molten
6 The metal extracted from aluminium oxide
7 The gas produced when aluminium oxide is decomposed.
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c5_10 Using electrolysis continued
2
Which of the following metals cannot be extracted by reacting their oxide with carbon?
Explain your choice.
copper
3
sodium
aluminium
iron
zinc
calcium
Explain the following observations, and where possible draw diagrams to illustrate
your answer.
a) Compounds of metals and non-metals are electrolytes.
b) Electrolytes must be liquid before an electric current can flow through them.
c) When molten aluminium oxide is electrolysed aluminium collects at the negative
electrode.
d) The amount of electrolyte decreases during electrolysis.
3
1
Electrode reactions
Use the circles to assemble the ionic equations for the reactions at the electrodes in
the extraction of aluminium from aluminium oxide. State at which electrode the reaction
takes place.
e−
Al
e−
Al3+
e−
2
O2−
O
e−
e−
Magnesium is a similar metal to aluminium; alloys of magnesium and aluminium are
used in the aircraft industry. Magnesium is extracted by the electrolysis of molten
magnesium chloride.
a) Magnesium chloride has the formula MgCl2. What are the formulae of the ions in
magnesium chloride?
b) Explain why molten magnesium chloride conducts electricity.
c) When magnesium chloride is electrolysed, magnesium metal is formed at the
negative electrode. Write the ionic equation for the reaction at this electrode.
d) Chlorine gas (Cl2) is produced at the positive electrode. Write the ionic equation for
the formation of chlorine.
e) What is the balanced chemical equation for the decomposition of magnesium
chloride?
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c5_11 What is special about metals?
Resources
Student Book pages 154−155 Homework pack c5_11
Files on Teacher Pack CD: c5_11_worksheet; c5_11_technician
Models, pictures and animations of the giant crystal lattice structure of metals; equipment for demonstration
Learning outcomes
C5. 4.23 understand the properties of metals related to their uses (limited to strength, malleability, melting point and
electrical conductivity)
C5.4.24 explain the physical properties of high strength and high melting point of metals in terms of a giant
structure held together by strong bonds (metallic bonding)
C5.4.25 understand that in a metal crystal there are positively charged ions, held closely together by a sea
of electrons that are free to move, and use this to explain the physical properties of metals, including
malleability and conductivity
Literacy focus: Writing descriptions of the appearance and properties of metals.
Numeracy focus: Collecting, using and comparing data on properties of metals.
ICT focus: Modelling giant structures to explain properties; software modelling to illustrate giant structures; internet
research on particular metals.
In this lesson students are learning to:
understand the properties that metals have that make them useful
explain how the structure of metals is related to their properties.
Key vocabulary
malleability metallic bond
Obstacles to learning
The crystal structure of metals is not obvious and the great diversity in properties of metals can make it difficult to
see that one theory can explain all the variations. Poor diagrams can give a picture of the metallic bond that bears
no relation to the incompressible nature of metals.
Stimuli and starter suggestions
Ask students to name some metals and the properties that they associate with them. Try to get them to think of a
wide variety of metals – e.g. mercury to tungsten.
Learning activities
worksheet c5_11
Low demand Demonstrate the properties of a variety of metals compared with other materials (see technician
sheet). Students should record what they observe and then write a few sentences summarising the properties of
metals. Make sure that students understand the terms ‘strength’, ‘malleability’ and ‘conductivity’ in the context of
the properties of metals. Students could then access data on properties of metals and design their own ‘Top
Trumps’ style game cards for metals – some data for this are given on the worksheet.
Teaching and learning notes: Students are not expected to recall data about metals, but they should have some
knowledge of the typical properties of metals and some examples which display them.
Standard demand Use models, pictures and computer animations to describe the giant crystal lattice structure of
metals and explain that there are strong forces between the atoms. Ask students to use this idea to explain the
strength and high melting point of metals. If time allows, students can investigate the history, properties, uses and
commercial importance of particular metals – both commonly used metals such as copper, and less well-known
such as indium.
Teaching and learning notes: Foundation tier students just need to know that a force exists between the atoms in
a metal that is called the metallic bond and that acts in all directions (unlike a covalent bond).
High demand (Higher tier) Explain the metallic bond in terms of the attraction that close-packed positive ions
have for free electrons (or electrons hopping between atoms). Note that metal atoms can lose their outer shell
electrons relatively easily. The force between (temporary) ions and electrons produces the resultant attractive force
between the atoms. Challenge students to use these ideas to explain electrical conductivity and the malleability of
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c5_11 What is special about metals? continued
metals (Student Book p.155 gives brief explanations.) Note that many diagrams of metal ions in a ‘sea of electrons’
do not show the positive ions closely packed – this can give an incorrect impression of the structure of metals. The
worksheet gives further tasks.
Plenary suggestions
Ask students to champion their favourite metal and, depending on ability, explain how its structure explains its
properties and uses.
Student Book answers
Q1 a) Electrical wires; b) Bridges, buildings, cars
c) Car bodies, aircraft, kitchen foil; d) Saucepans, car engines
Q2 Steel is strong because it has a strong force of attraction between the atoms.
Q3 A lot of energy is needed to overcome the strong force of attraction between the atoms.
Q4 There is a strong force of attraction between the tungsten ions and the ‘free’ electrons between them.
Q5 There are ‘free’ electrons between the ions in the silver crystal that can move and carry a current.
Q6 When a sheet of aluminium is bent, the layers of atoms move to a new position with the same pattern/
arrangement/structure, so it is as strong as it was before.
Worksheet answers
Activity 1 (Low demand)
Q1 a) (i) Nickel; (ii) silver; (iii) tungsten; (iv) rhodium
b) Lead, tin and zinc; (c) Iron/steel
Q2 Bridges – strong; e.g. iron/steel
Saucepans – high melting point; e.g. iron/steel, copper, aluminium
Electrical components –- conduct electricity; e.g. copper, silver, gold, aluminium
Car bodies – malleable; e.g. iron/steel, aluminium
Activity 2 (Standard demand)
Q1 a) All the particles are the same. (Foundation students are not expected to know about the free electron/ion
structure of metals.)
b) The atoms are arranged in a regular structure of layers.
c) The same structure is repeated over and over again for a very large number of particles.
Q2 High strength and melting point are explained by the metallic bond being a strong force between the atoms.
Activity 3 (High demand)
Q1 a) Diagrams showing close-packed positive ions surrounded by free electrons moving randomly when current is
off and in one direction when the current is on.
b) Diagrams showing regular arrangement of positive ions in layers (free electrons not necessary) with layers
shifting relative to each other but not changing the arrangement.
Q2 Tin is much weaker and lower in melting point than tungsten; hence it has much weaker metallic bonds, weaker
forces between the fixed ions and the free/ sea of electrons.
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c5_11 What is special about metals?
Technician sheet
Equipment and materials
Demonstration
sheets or rods of aluminium, steel, zinc, copper, etc.
copper wire
lumps or rods of sulfur and carbon (graphite)
ceramic materials – glass, pottery, china
glass rod drawn out to produce a thin section – diameter roughly the same as that of the
copper wire, and the end shaped into a hook
power pack, light bulb in holder, leads and crocodile clips
hammer
G-clamp or vice
Bunsen burner, tongs
clamp stand
hanging weights
Method
Demonstrate the properties of metals in comparison with non-metallic materials.
Malleability – bend pieces of each metal. It may be useful to clamp the sample before
attempting to bend or hammer it into a different shape. Repeat the exercise with the nonmetallic materials to show that they are brittle.
Melting point – hold a piece of the material in a blue Bunsen flame and show that the metal
does not melt. It is best to use steel or copper for this. Ceramics also have high melting
points. Do not test sulfur, because it has a low melting point and burns to produce toxic
sulfur dioxide.
Electrical conductivity – complete an electric circuit with each of the materials in turn.
Show that the lamp lights only with the metals.
Strength – suspend a length of copper wire from a clamp stand and hang weights from it.
Repeat with the glass rod clamped vertically, carefully hanging a weight hanger from the
hook end. It will almost certainly snap very easily, demonstrating that glass ‘wires’ are not
strong in tension.
Health and Safety notes
Take care when testing glass and ceramics, because sharp pieces can be formed when
they break (especially the glass rod) – wear goggles.
Students can carry out each of the tests under supervision, but ensure that they are
wearing goggles.
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c5_11 What is special about metals?
1
1
Properties of metals
Use the data list on metals (at the end of this worksheet) to answer the following
questions.
a) Which metal:
(i) is the strongest
...................................
(ii) is the best electrical conductor
...................................
(iii) has the highest melting point
...................................
(iv) is the most expensive?
...................................
b) Which metals melt below 500 °C?
...................................................................
c) Which metal is stronger and cheaper than magnesium? .........................................
2
Match up the uses and properties of metals and write in the name of a metal that may
be used for each purpose.
Bridges (......................................)
Saucepans (...................................)
Electrical components
(....................)
Car bodies (.................................)
3
high melting point
malleable
strong
conduct electricity
‘Metals Top Trumps’
Design cards to display the property data for each metal.
Share the cards between the players – face down.
The first player turns over a card and calls out a property – e.g. highest melting point or
lowest price.
Each player then turns over their top card. The player with the metal that is best in the
named category wins all the cards in that round and has the choice of property in the
next.
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c5_11 What is special about metals? continued
2
1
The structure of metals
The structure of metals is described as a ‘giant
crystal lattice of atoms’. Use a named metal in
your answers.
a) Why is the word ‘atoms’ used?
b) What does the term ‘crystal lattice’ mean?
c) What does the word ‘giant’ mean when used
to describe the structure of materials?
© Science Photo Library
2
3
1
Choose a metal from the data list below and explain how the bonding in its structure
accounts for its strength and melting point. Use any applications of the metal that you
know about to illustrate your answer.
The metallic bond
Draw diagrams of the structure of a metal to show what happens when:
a) an electric current is switched on and off
b) one layer of metal ions slides over another layer when a metal is stretched or bent.
2
Compare the metallic bonding in tin and tungsten using the data from the list below.
Explain the difference in properties of the two metals by referring to the strength of the
metallic bond in the two metals.
Data on metals
Name
Melting point
(°°C)
Aluminium
660
Chromium
1857
Copper
Strength
(MPa)
Price
(£ per kg)
41
2.6
8
8
7.4
1083
43
64
9
Gold
1064
22
49
33,000
Iron/steel
1535
34
11
0.27
Lead
328
1.5
5
2.3
Magnesium
649
22
26
1.8
Nickel
1455
99
16
24.4
Rhodium
1966
95
23
150,000
Silver
962
35
67
800
Tin
232
1
9
29
Titanium
1660
23
2
27
Tungsten
3410
12
20
24
420
14
18
2.1
Zinc
Notes:
11.4
Electrical conductivity
6
−1
(×
×10 S m )
Strength – the higher the value, the stronger the metal
Electrical conductivity – the higher the value, the better the metal conducts
Price – varies daily
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c5_12 Metals in the environment
Resources
Student Book pages 156−157 Homework pack c5_12
Files on Teacher Pack CD: c5_12_worksheet
Metal products
Learning outcomes
C5.4.26 evaluate, given appropriate information, the impacts on the environment that can arise from the extraction,
use and disposal of metals.
Ideas about Science
IaS 5.1 everything we do carries a certain risk of accident or harm. Nothing is risk free. New technologies and
processes based on scientific advances often introduce new risks
IaS 6.1 science-based technology provides people with many things that they value, and which enhance the
quality of life. Some applications of science can, however, have unintended and undesirable impacts on the quality
of life or the environment. Benefits need to be weighed against costs
IaS 6.2 scientists may identify unintended impacts of human activity (including population growth) on the
environment. They can sometimes help us to devise ways of mitigating this impact and of using natural resources
in a more sustainable way
IaS 6.5 some forms of scientific research, and some applications of scientific knowledge, have ethical implications.
People may disagree about what should be done (or permitted)
IaS 6.6 in discussions of ethical issues, one common argument is that the right decision is one which leads to the
best outcome for the greatest number of people involved. Another is that certain actions are considered right or
wrong whatever the consequences
Literacy focus: Reading, discussing and writing open responses to questions of the ethical uses of metals.
Numeracy focus: Using data on the consumption of metals.
ICT focus: Using the internet to investigate the costs and benefits of using metals.
In this lesson students are learning to:
discuss the risks of extracting, using and disposing of metals
evaluate the impact on the environment of our need for metals
consider how we can deal with undesirable effects of using metals.
Obstacles to learning
This topic is open-ended with many questions that do not have right answers. Students will need a broad and
open-minded approach to achieve success.
Stimuli and starter suggestions
Show some products that are made from or contain metals – e.g. an aluminium can, a steel knife, a copper pipe
or wire, a battery, a mobile phone. Ask students to discuss who benefits and who is harmed by the use of the
materials in these products. Note whether they consider the source of the metal and how it is extracted or how it
is disposed of or just consider the function of the objects themselves.
Learning activities
worksheet c5_12
Low demand Ask students to discuss the hazards of using metals. For example: sharp edges – cuts; density/
weight – crushing; burns – using hot metal; toxic – mercury, lead, cadmium (plus others that are less hazardous
such as copper). Move on to hazards to the environment of our use of metals with the aid of pictures as stimulants:
how metals are obtained – recall the big quarries for copper etc.; pollution from metal extraction – pictures of
steelworks; pollution from careless disposal – pictures of scrap heaps and metal waste dumped in countryside; the
effects of all these – habitat destruction, poisoning of wildlife (and human populations). Note the variety of metals
used today – not just iron, copper and aluminium, but catalysts (rhodium), electronics (indium, etc.) magnets
(neodymium). The worksheet provides tasks which focus on these ideas.
Teaching and learning notes: There is no new content in this lesson. The emphasis is on the IaS statements –
the implications for the environment of technological developments in the past, present and future and the
responsibilities they bring.
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c5_12 Metals in the environment continued
Standard demand One approach is to carry out a case study of a metal. Student Book p.157 uses copper, but it
could be any example from a traditional bulk metal like iron to a component of modern technology such as
neodymium in modern electric motors. Individually or in groups, students could research different metals and report
back to the class. Make sure that students focus on the environmental impact of the use of their metals and how
scientists may have been responsible for the problems and have found (or not) ways of mitigating them by limiting
the amount of metal used, finding alternative materials or processes and recycling.
Teaching and learning notes: Students will need access to the internet. Ascertain regularly that they are focusing
on the contents of the IaS statements.
High demand Students should discuss the ethical implications of the extraction, use and disposal of metals (IaS
6.5, 6.6). For example, should scientists pursue research when they know it will mean that additional resources of
metals will need to be exploited with the consequent impact on the environment? The Student Book uses the
example of lithium batteries being used on a much larger scale in vehicles.
Plenary suggestions
Ask students to give their conclusions to their deliberations. Is our use of metals justified? Do scientists have a
beneficial or harmful effect? Do improvements in technology increase or decrease the harm to the environment or
the sustainability of resources?
Student Book answers
Q1 Quarries/mines destroy habitats; pollution from extraction damages plants and animals; metal waste in landfill
sites destroys habitats; contaminated soil and water kills wildlife.
Q2 Some metals are toxic; they kill plants and animals; break foodwebs, etc.
Q3 Digging up the ore and dumping the waste rock; acid rain from sulfur dioxide emissions; dumping scrap metal
contaminates land and water.
Q4 For: new jobs; guarantees supply of metal
Against: increased local pollution; destruction of habitats; inconvenience and disruption of life (NIMBY)
Q5 Increased the variety of metals used; increased use of rare metals that are more difficult to extract; more waste
and pollution; new sites disturbed by mining.
Q6 For: electric cars use up a lot of lithium needed for batteries for electronic goods
Against: lithium not rare; could be recycled
Worksheet answers
Activity 1 (Low demand)
Q1 a) Aluminium cans are lighter and less breakable than glass bottles.
b) Miners who dig the ore out of the ground; workers in the aluminium foundries at risk of electrocution or burns.
c) Destruction of habitats at mines; use of energy resources damages the environment; release of carbon
dioxide adds to global warming.
d) Can harm animals – sharp edges, cuts; cans act as traps.
e) Recycling would reduce the amount of mining needed, the amount of energy used and the amount of carbon
dioxide released and stop waste aluminium cluttering up the countryside.
Q2 Answers should include the effects of quarrying on loss of habitats, the metals extraction industry producing
pollutants and carbon dioxide and the disposal of toxic metals that can kill plants and animals (and people).
Activity 2 (Standard demand)
Q1 Answers should include the more metals that are used: more mining is needed; more pollution is produced by
extraction methods; the more difficult it becomes to separate metals for recycling.
Q2 This could be an individual or group activity – statements provided are:
For: scientists shouldn’t make use of metals that are hazardous; new technology that uses metals has harmed
the environment and affected health; new products often have harmful effects that scientists had not expected.
Against: there are risks in everything that we do; modern uses of metals have given us products that have
improved life; scientists could make sure that new products cause less harm and use resources more
sustainably.
Activity 3 (High demand)
Q1 a) Benefit – cancer patients; harmed – people who live and work in nuclear power stations that may malfunction
b) Benefit – gadget buyers; harmed – the environment in Africa and people who live near the mines
c) Benefit – everyone; harmed – the environment and inhabitants of the Atacama Desert
The decisions are up to the student – there are no correct or incorrect answers.
COLLINS NEW GCSE SCIENCE
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OCR 21st Century Science: C5 Chemicals of the natural environment
c5_12 Metals in the environment
1
1
Hazards of use
A lot of aluminium is used today to make soft-drinks cans. Answer the questions about
our use of aluminium. You can use the information in the boxes to help you.
Broken aluminium
cans can cut animals
and trap them
The extraction of aluminium
releases a lot of carbon dioxide
gas into the air
The extraction of aluminium from its
ore use a very large electric current
and a temperature of over 1000 °C
Glass bottles are
heavy and easily
smashed
Aluminium ore is dug from
huge quarries in South
America and Africa
Melting and reusing old aluminium
cans uses far less energy than
extracting new aluminium
a) Why have aluminium cans replaced the glass bottles used previously?
................................................................................................................................
................................................................................................................................
b) Which people are most risk of being harmed by our use of aluminium?
................................................................................................................................
c) How does the extraction of aluminium harm the environment?
................................................................................................................................
................................................................................................................................
d) What impact does the disposal of aluminium cans have on the environment?
................................................................................................................................
................................................................................................................................
e) What could be done to reduce the effects of your answer to parts (c) and (d)?
................................................................................................................................
................................................................................................................................
2
Think about some of the metals that you use every day.
Copper is obtained from huge quarries, where 99% of the rock dug up is waste.
Iron is the metal used in the largest quantities. Steelworks producing iron use lots of
coal and release large amounts of carbon dioxide gas and other pollutants such as
sulfur dioxide.
Lead, mercury and cadmium, used in many types of battery, are highly poisonous if
released into the environment.
Design a poster or presentation or write a blog describing how our use of metals can
harm the environment.
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c5_12 Metals in the environment continued
2
1
Costs and benefits
Smartphone technology makes use of many unusual metals, including lithium, indium,
neodymium, tantalum, zirconium, beryllium and gallium, among others. Each of these
metals has to be found in rocks, mined, extracted from its compounds, used in a
product and finally disposed of.
Discuss the impact that the designers of smartphones are having on the environment.
2
People have different views about our uses of metals.
Scientists shouldn’t make use
of metals that are hazardous
Scientists could make sure
that new products cause
less harm and use
resources more sustainably
Modern uses of
metals have given us
products that have
improved life
New products often have
harmful effects that scientists
had not expected
New technology that
uses metals has
harmed the
environment and
affected health
There are risks in
everything we do
Prepare short presentations for and against the following statement:
‘Scientists developing the use of metals in modern technology have caused risks to
health and harm to the environment that are greater than the benefits.’
3
1
2
Metal ethics
Consider the following case studies – in each, suggest arguments for and against the
course of action suggested. Consider who might be affected, and who and how many
might benefit.
a) Technetium is a very rare metal used in gamma ray imaging for detecting cancer
and also in treatments for cancer. The only source of technetium is from special
nuclear reactors, which people fear could release radiation. It is suggested that
new nuclear reactors are needed to supply technetium.
b) Tantalum is a metal with particular electrical properties that make it essential for
modern electronic gadgets. To provide more of the metal, mines may have to be
opened in national parks in central Africa. Civil wars have already been fought in
parts of Africa where other essential minerals have been mined.
c) One answer to global warming is to use lithium batteries to store electricity from
renewable resources. This will need a big increase in the amount of lithium
extracted. The likely source is from mining the Atacama Desert in Chile, which has
a very vulnerable ecology.
Investigate the use of one metal that is important for modern technology.
a) Find out about the sources of the metal and the health risks of the metal and its
compounds.
b) Consider who benefits from the use of the metal and who is likely to be harmed by
it. Are the benefits and the harm experienced by a few people or many?
c) Consider whether or not new applications should be found for the metal, which will
increase its consumption. What could scientists do to lessen the harm caused by
the use of the metal?
d) Present your findings and opinions as a poster, a presentation, a TV- or radio-style
discussion – or any other format you can think of.
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