Download Chemistry Post-Enrolment Worksheet C

Name:_________________________________
Chemistry Post-Enrolment Worksheet
The purpose of this worksheet is to get you to recap some of the fundamental concepts that you studied at
GCSE and introduce some of the concepts that will be part of the first term at AS level.
Please complete the worksheet and bring sections 1 to 4 to your first chemistry lesson.
If you need help answering any of these questions, you can use the links provided in each section. You will
find a copy of the periodic table on the back page that you can use to help you answer the questions.
Section 1 – The Mole
The molar mass of a substance is the mass (in g) of one mole of a substance.
For Example 12g of Carbon contains one mole of C atoms 
 18g of water contains 1 mole of water molecules
Carbon
12.0
C
6
1) How many moles of the following are there?
a) 32g of sulfur atoms
c) 132g of CO2 molecules
b) 20g of calcium atoms
d) 3.16kg of KMnO4 (1kg = 1000g)
(4 marks)
This helps us to understand the equation that links number of moles with mass – the equation you will
have been taught at school is:
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 =
𝑚𝑎𝑠𝑠 (𝑔)
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
The mole is in fact just a counting tool. In the same way that a couple = 2 and a dozen = 12, one mole of
any substance = 6.02 x 1023 particles of that substance.
E.g., 5 moles of sodium will contain 5 x 6.02 x 1023 individual sodium atoms.
2) Calculate the number of atoms in the following:
a) 2 moles of carbon atoms
c) 8g of sulphur atoms
b) 0.5 moles of mercury atoms
d) 3kg of magnesium atoms
(4 marks)

For help with this section, try the following link;
http://www.chem1.com/acad/webtext/intro/int-2.html
Section 2 – Percentage Mass Calculations
When dealing with compounds we can calculate the percentage by mass of each element that it contains.
For example, carbon dioxide contains carbon and oxygen:
12/44 x 100 = 27% Carbon
(2 x 16) / 44 x 100 = 73% Oxygen
3) Calculate the percentage mass of;
a) magnesium in magnesium oxide
c) nitrogen in NH4NO3
b) lithium in lithium oxide
d) copper in Cu2(OH)2CO3
(4 marks)

For help with this section, try the following link;
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/chemcalc/chemcalc_bot
hrev5.shtml
Section 3 – Balancing Chemical Equations
To represent a chemical reaction we could write a word or symbol equation. At A level, you will be
expected to interpret, construct and balance symbol equations.
CH4 + 2O2

CO2 + 2H2O
In order to balance an equation you must make
sure the number and type of each atom is the
same on both sides of the equation – this is not
always as easy as it sounds!
4) Write out balanced symbol equations for the following reactions:
a) lithium + water → lithium hydroxide (LiOH) + hydrogen (H2)
b) nitrogen (N2) + hydrogen → ammonia (NH3)
c) ethane (C2H6) + oxygen (O2) → carbon dioxide + water
d) ethanol (C2H5OH) + ethanoic acid (CH3COOH) → ethyl ethanoate (C2H5OOCCH3) + water
(12 marks)

For help with this section, try the following link;
http://www.ausetute.com.au/balcheme.html
Section 4 – Writing the Formulae for Ionic Compounds
In simple terms, ionic compounds are those which contain a metal and a non-metal. The overall charge of
an ionic compound is zero, therefore the charges of the ions that make up the compound must add up to
zero.
e.g. sodium chloride is made up of Na+ ions and Cl- ions. The overall formula is NaCl
lithium oxide is made up of Li+ ions and O2- ions. The overall formula is Li2O
Polyatomic ions are those that contain more than one atom e.g. the hydroxide ion (OH -), which is made up
of an oxygen atom and a hydrogen atom and has an overall 1- charge. Brackets can be used if we need
more than one of a polyatomic ion in our formula.
e.g. ammonium carbonate is made up of ammonium ions, NH4+ , and carbonate ions, CO32In order for the charges to balance we need two ammonium ions for every one carbonate ion
therefore the formula becomes (NH4)2CO3
5) Using the ions given below, write the overall formulae of the following ionic compounds:
a) zinc oxide
c) copper sulfate
b) potassium sulfate
d) calcium hydroxide
(4 marks)
zinc = Zn2+, copper = Cu2+, potassium = K+, calcium = Ca2+, sulfate = SO42-,
hydroxide = OH-, oxide = O26) Write a symbol equation to show that magnesium carbonate decomposes into magnesium oxide and
carbon dioxide. [magnesium ion = Mg2+]
(3 marks)

For help with this section, try the following link;
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/bonding/ionic_bondingrev7.shtml