Download The Chemistry Handbook - A2

THE CHEMISTRY HANDBOOK
A2-LEVEL
NAME:________________________ TEACHER:__________________
WHERE WILL IT TAKE YOU?
______________________________
CONTENTS
PAGE
Introduction
The Chemistry A-Level Commitment
3
4
Assessment Information & Record of Achievement
Internal Assessment
Record of achievement - End of unit tests & Internal mock exams
Record of Achievement - Homework
External Assessment information
6
7
8
9
General Information
Mathematical Requirements
Strategies for reaching and exceeding your target grade
Homework
11
12
13
Contact with your teacher
13
Tools
Reading Lists
Television / DVD / iplayer
Phone Apps
Internet
Definitions
Graphs
Table of common ions and molecules
Properties of common acids/alkalis/bases
Equations
Balanced equations
Practical Techniques
Practical Observations
Practical Accuracy (experimental error)
Significant Figures
Yields
Hazards /precautions
GCE Chemistry Data Sheet
The Periodic Table of the Elements
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Introduction
Welcome back to the Helsby High School Chemistry A-level course. This handbook is aimed at
providing you with a reference source for some common queries on some common subjects. Keep
it handy for the duration of your course and refer to it often.
To compliment this hand book there are also a series of ‘How to…’ booklets available on Moodle.
If you are stuck on anything then refer to these booklets, and if you have any improvements
that you can suggest email me at [email protected].
The specification that you will be following is the AQA GCE (AS & A Level) Chemistry
specification. You will be given the specifications for the units of the course by your teachers,
keep them in your file so you can refer to them in lessons and at home. The specifications tell
you what the exam board expects you to know and do. You can also find the specification on the
AQA website.
You have studied Chem 1 and Chem 2 for AS-level and you will study Chem 4 and Chem 5 for Alevel. You will also be completing a practical element of the course which is contained within
Chem 6 (A2). Any theory that you have learnt in Chem 1, 2, 4 & 5 may be needed/used/tested
within this practical unit.
Come to the edge.
We might fall.
Come to the edge.
It’s too high!
Come to the edge!
And they came,
And he pushed,
And they flew….
Christopher Logue, ‘Come to the Edge’, 1969
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The Chemistry A-level commitment
Chemistry A-level is a highly sought after commodity by individuals, universities and employers.
In addition to teaching you a particular branch of science it helps you develop your transferable
skills such as problem solving, analysis, evaluation and communication skills. With Chemistry you
can enter medicine, law, banking, office based work, engineering, architecture and of course
work in the Chemical industry in a variety of careers.
But as with anything worth having in life you need to work at it. Chemistry A-level requires a
commitment - if you commit you will succeed. The commitment you make when choosing the Alevel Chemistry course is as follows;

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To commit to 9 hours per fortnight of independent study most of which will be directed
by your teacher in the form of homework.
To commit to using all the resources at your disposal while completing all your homework
to the best of your ability.
To commit to handing your homework in before or on the deadline given by your teacher.
To come to lessons fully equipped including pens, pencils, rulers, erasers, calculator, text
book, file, paper, planner, lab coat and a periodic table.
To keep an organised and complete file of notes, work completed & homework that is
brought to every lesson.
To attend every lesson and arrive on time and ready to work.
To revise fully and effectively for every internal unit test & mock exam as well as for all
external exams.
I have read and understood the commitment necessary to succeed at A-level Chemistry.
Signed: __________________________
date:___________________
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ASSESSMENT
INFORMATION &
RECORD OF
ACHIEVEMENT
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Internal Assessment
Between September and May you will be assessed within each module (Chem 4 & 5) through a
series of standard homework tasks, end of unit tests and mock exams. The result of these
assessments will contribute to your attainment level which will be reported to you at regular
intervals but particularly at consultation evenings and in written reports. Your reported
attainment level is aimed at giving you an indication of what level you are working at and whether
you are on or above target. It will also be used to inform the grades reported on your UCAS
application form.
The assessment tasks within the academic year are;
Chem 4:
o
o
o
2 x mock exams
5 x end of unit tests
5 x standard homework tasks
o
o
o
2 x mock exams
4 x end of unit tests
4 x standard homework tasks
o
2 x standard ISA homework tasks
Chem 5:
ISA:
You will also be given normal homework tasks which are aimed at helping you learn.
Each assessment task will be given a different weighting when applied to the calculation of your
overall attainment level for each module and your overall attainment.
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Record of achievement - End of unit tests & Internal mock exams
My Target Level is: _________
It is very important that you take all tests and exams seriously and revise well. These tests will
closely match what you will need to do in the external A-level exams. From the results you will be
able to identify areas you need to work on – this could be knowledge based or exam technique.
Record the details of all your internal assessments in the table below.
Date
Subject of end of unit test or
internal exam
Mark &
grade
CHEM 4
Carbonyls
Aromatics & Acylation
Amines, Amino Acids & Polymers
Rates & Equilibrium
pH
CHEM 5
Periodicity
Redox
Thermodynamics
Transition Metals
MOCKS
Mock 1
Mock 2
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Possible improvements
Record of Achievement - Homework
My Target Level is:________
It is very important that you put the maximum amount of effort and thought into your
homework. It is part of the learning process. Use the table below to record details of your
standard homework tasks and attainment.
Date
Task
Mark &
grade
CHEM 4
Carbonyls
Organic Synthesis
Structure Determination
Rates & Equilibrium
pH
CHEM 5
Redox
Thermodynamics
Transition Metals – Complexes &
Aqueous Chemistry
Transition Metals – Redox Reactions &
Catalysts
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Possible improvements
External Assessment information
You have completed the Chem 1 and Chem 2 papers, if you think a resit would help your overall
attainment then discuss the appropriate time to take the resit with your teacher. Chem 4 and
Chem 5 papers will be taken in the June of Year 13.
For Unit 6 the school follows the CHM6T route. The PSAs will be completed during normal
practical lessons (the best six, each worth 2 raw marks, will be submitted to the exam board).
There will be two opportunities in Year 13 to complete the ISA (only one will be submitted to the
exam board). The ISAs consist of a 2 hour practical exam followed within a week by a 1 hour
written exam and are usual held in the Jan/Feb & April/May of each year.
Record the date of your external exams in the table below.
ISA 1
ISA 2
Chem 4
Chem 5
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GENERAL
INFORMATION
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Mathematical Requirements
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Strategies for reaching and exceeding your target grade
The following are a list of strategies proven to help students reach and exceed their target
grade:
1.
Review work done in class by reading around the subject. Look up web sites on the
internet and read for understanding. Read (for understanding) your notes and text book.
If it doesn’t make sense keep researching and working through the problem until it does.
2. Complete all homework set to a high standard.
a. To do this you must first understand the area of chemistry it relates to (by
looking at notes and reading around the subject),
b. Secondly try the homework questions using the text book and notes to help you,
c. Thirdly check your answers,
d. Finally review your answers prior to handing it in.
In this whole process make sure you
 focus and concentrate on the work completely (no music, TV or chatting),
 correct any mistakes.
 Check : units; calculations; rearranging of equations; inputs into calculators; use
of words e.g. is it molecules or ions?; definitions; state symbols; chemical
equations; charges; is it logical?; do you contradict yourself?; does it actually
answer the question?; does it cover all the mark points?; have you written down
all relevant working out?; Have you made all numerical substitution into equations
clear?; Have you written down all relevant information or have you summarised it
too much?; Have you used full sentences?
3. If you have finished work set then devise your own study e.g. practise exam questions
which can be found in the text book, on Moodle and on the AQA website –
www.aqa.org.uk/qualifications/a-level/chemistry-key-materials
4. Memorise important information such as definitions, equations, sequences, examples.
5. Organise your file.
6. Organise your life by organising your work time and play time so your play time does not
affect your work time.
7. Organise your study time so you make the most of it.
8. Learn definitions off by heart.
9. Don’t study in the break out space – you are wasting your time! Study in the library or
the other quiet study areas for Year 12 & 13.
10. Be strict with your work ethic at school. You should be working between 9am and 3.05pm.
The only time you should be taking a break from work in school is between 11am to
11.15am and 1.20pm to 2pm. This means you need to use your study periods productively.
11. Draw up mind maps & spider diagrams for each topic. Make brief notes using your text
book and internet searches.
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12. Keep reviewing and revising past work – you will need it.
13. Read for understanding again! Make connections. If anything doesn’t make sense don’t
leave it until tomorrow, try to understand it today by concentrating on trying to
understand it. Read for understanding again!
14. You must spend at least 9 hours a fortnight outside lessons on Chemistry homework &
review.
15. Review marked homework. Analyse to understand why you got things right and why you
missed marks. Don’t make the same mistake twice!
Homework
You are expected to complete homework set by the deadline given. Follow the advice given in
step 2 in the section ‘Strategies for reaching and exceeding your target grade’ as well as the
advice below.
Do
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Start the homework the day you are given it
Using all the resources available, including text books and notes, complete and
review at least twice more before handing it in
Leave time to be able to work on any problems you encounter
Arrange to see your teacher at least 2 days before the homework is due if you are
having problems
Attempt all homework questions
Do Not
 Go to your teacher the day the homework is due and tell them you couldn’t do it
 Hand in incomplete HW
 Fail to hand in the HW on time
Contact with your teacher
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
You have 9 lessons of Chemistry a fortnight in which you can ask anything. If you are
struggling outside of class, although it is always better to try and solve a problem
yourself (even if it takes you hours – you will learn from the experience) then ask
because if you are having problems then you can bet other people are having problems
and your teacher will either go over the relevant area again in class or arrange a separate
tutorial at lunch time.
BUT: before asking your teacher will expect you to have had a go at the problem and be
able to tell them what you have done to try and solve the problem yourself.
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TOOLS
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Reading List
Core text books (provided by the school on loan)
1. AQA Chemistry AS, Nelson Thornes (for Year 12)
2. AQA Chemsitry A2, Nelson Thornes (for Year 13)
Support material (Available for purchase at various outlets such as Amazon)
3. Student support material for AQA AS Chemistry Unit 1: Foundation Chemstry
4. Student support material for AQA AS Chemistry Unit 2: Chemistry in Action
5. Student support material for AQA AS Chemistry Unit 4: Kinetics, Equilibria and Organic
Chemistry (Year 13)
6. Student support material for AQA AS Chemistry Unit 5: Energetics, Redox and Inorganic
Chemstry (Year 13)
7. There are many revision books available, choose one that is appropriate to your learning style.
Ensure it is for the AQA syllabus being studied.
Other useful books (available to use in the Chemistry Dept.)
8. Calculations in AS/A Level Chemistry, Jim Clark, Longman
9. Advanced Level AS Chemistry for AQA, J. Atkinson & C. Hibbert, Heinemann
10. Advanced Level A2 Chemistry for AQA, J. Atkinson & C. Hibbert, Heinemann
Other – for reading around the subject
11. Bill Bryson: A short history of everything
12. Periodic Tales, Hugh Aldersey-Williams
13. The Elements – A very Short Introduction, Philip Ball
14. Molecules – A very Short Introduction, Philip Ball
15. Molecules at an Exhibition, John Emsley
16. The Periodic Kingdom, Peter Atkins
Television / DVD / iplayer
Watching scientific television programs related to Chemistry is sometimes a more enjoyable way
of broadening your Chemistry knowledge. Watch out for science related programs or try to get
hold of the following TV & radio programs.
Possible TV programs to watch out for:
 Bang goes the theory
 Brainiac (a bit of fun!)
Past TV programs which are now on DVD, BBC website, iplayer or even Youtube:
 Chemistry: A Volatile History with Prof. Jim Al-Kahlili
 Earth: The power of the Planet with Dr. Iain Stewart
Radio programs:
 Radio 4 – Material world
APPs for phones
Look out for any mobile phone apps. There are many periodic table and Chemistry quiz question
apps available for free.
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Internet
1. Moodle
You can access Moodle from any computer within school or outside of school. If you go to the
school website there is a link to the Moodle log in page. Your login details are the same as your
normal login details for accessing the school system.
On Moodle there are various resources that will be helpful to you over the course of the year
such as the Standard homework you will be set & past papers.
2. www.aqa.org.uk/qualifications/a-level/chemistry-key-materials
The AQA board website is where you will find the course specifications, examiners reports, past
paper questions & answers.
3. The following are a list of websites that contain information to help you with homework,
review work or revision. I have not vetted all of these web sites so when using them read for
understanding – if they don’t make sense then check the chemistry.
 www.s-cool.co.uk/a-level/chemistry
 www.chemguide.co.uk
 alevelchem.com
 www.docbrown.info
 www.chembook.co.uk
4. Kerboodle
It is hoped that the department will be offering access to the Kerboodle learning package. You
will be told your password and login details which you should keep safe.
Centre ID:_____________________
Username:_____________________
Password:_____________________
Definitions
It is essential that you learn all the definitions you come across (and there really is NO
substitute to just memorizing them). The text books you are provided with have a glossary of
definitions at the back of the book. Use the table below to record any that you want to have
quick reference to. It is very important in Chemistry to be precise in your definitions.
Unit
Word
Definition
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Graphs
Graphs are easy to get full marks on if you follow these pointers.
 The plotted points must take up at least half a page. Make sure the plotted points are
accurate – you will get marked on accuracy.
 Complete the axis / points / lines of best fit in sharp pencil
 Make sure the axis are drawn on the major lines of the graph paper, not between or
coming off the lines
 Label all axis and give the graph an overall title
 Put units onto the axis. Check the units e.g. should it be J (Joules) or kJ (kilojoules)
 Use sensible and equally spaced numerical graduations on the axis
 Know how to draw (and practise) lines of best fit
 If asked to extrapolate a graph continue the line of best fit to the point specified
 Make the lines of best fit a singularly drawn line not sketched or thick
 Should the line of best fit go through the origin? If so draw it through the origin. (you
will have to use your scientific knowledge to determine this and will be able to do this by
gaining experience through the course).
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Table of common ions and molecules
You will need to know these common ions so you must memorise them. You will use them
throughout your Chemistry A-level. There are gaps in the table so you can add to the ions as you
learn more.
Positive ions
H+
Li+
K+
Mg2+
Ca2+
Zn2+
Cu2+
Fe2+
Co2+
Al3+
Fe3+
Cr3+
NH4+
Pb2+
Negative ions
FClBrIO2S2OHNO3NO2HCO3CO32SO42CrO42Cr2O72MnO4C2O42-
Hydrogen ion
Lithium ion
Potassium ion
Magnesium ion
Calcium ion
Zinc ion
Copper (II) ion
Iron (II) ion
Cobalt ion
Aluminium ion
Iron (III) ion
Chromium ion
Ammonium ion
Lead ion
Fluoride ion
Chloride ion
Bromide ion
Iodide ion
Oxide ion
Sulfide ion
Hydroxide ion
Nitrate (V) ion
Nitrate (III) ion
Hydrogencarbonate ion
Carbonate ion
Sulphate ion
Chromate (VI) ion
Dichromate (VI) ion
Manganate (VII) ion
Ethandioate ion
You will need to know these common molecules so you must memorise them. You will use them
throughout your Chemistry A-level.
Formula
H2
F2
Cl2
Br2
I2
O2
N2
CH4
NH3
SO2
NO
NO2
CO
CO2
Name
Hydrogen
Fluorine
Chlorine
Bromine
Iodine
Oxygen
Nitrogen
Methane
Ammonia
Sulphur dioxide
Nitrogen monoxide
Nitrogen dioxide
Carbon monoxide
Carbon dioxide
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Properties of common acids/alkalis/bases
Acids
Bases
Slippery to touch
pH > 7
turns red litmus blue
turns phenolphthalein pink
Turn methyl orange to yellow
When soluble in water contain OH- ions
Sour
pH < 7
turns blue litmus paper red
corrosive
Turn methyl orange to red
Contain H+ ions when in solution
Alkali: Has two possible definitions
1) A basic (as in it is a base) salt of an alkali metal (Group 1) or alkaline earth metal (Group
2).
2) A base that dissolves in water
General chemical reactions of acids
 Acid + Metal → Salt + Hydrogen
e.g. 2HCl + Mg → MgCl2 + H2

Acid + Metal oxide → Salt + Water
e.g. 2HNO3 + MgO → Mg(NO3)2 + H2O

Acid + Metal hydroxide → Salt + Water
e.g. H2SO4 + Mg(OH)2 → MgSO4 + 2H2O

Acid + Carbonates → Salt + Water + Carbon Dioxide
e.g. 2HCl + MgCO3 → MgCl2 + H2O + CO2

Acid + Bicarbonates → Salt + Water + Carbon Dioxide
e.g. HNO3 + Mg(HCO3)2 → Mg(NO3)2 + H2O + CO2
Some common acids – with their common states
1) Hydrochloric acid – HCl gas dissolved in water to make a solution
2) Sulphuric acid – solution
3) Nitric acid – solution
4) Citric acid – solid
5) Ethanoic acid – liquid (in solution is vinegar)
6) Tartaric acid – solid
7) Phosphoric acid - solution
Some common bases - For the following then sodium can be substituted for other group 1 or
group 2 metals
8) Sodium hydroxide – solid, dissolves to form a solution
9) Sodium Carbonate – solid
10) Sodium hydrogencarbonate – solid
11) Sodium Oxide - solid
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Equations
Equations represent what happens when chemical reactions take place.
There are different types of equation and you will need to be able to use the correct equation in
the correct context.
Word equations
Describes how a reaction progresses.
e.g.
Magnesium + oxygen → Magnesium oxide
Symbol equations - Formula equations
These are equations using the formulae of substances that show how many atoms of each
element are involved and where they go in the products.
e.g.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Symbol equations - Ionic equations
These equations only consider the ions taking part in the reaction
e.g.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
if the equation is split into just the reacting ions
H+ + Cl- + Na+ + OH- →
Na+ + Cl- +
H 2O
we can cancel the ions that don’t change and appear on each side of the equation so overall the
ionic equation is
H+ +
OH- →
H 2O
Symbol equations - Ion-electron equations / Half equations
These show the ionisation of the species.
Li+(g)
e.g. Li(g) →
+
e-
When asked for an equation in a question a balanced symbol equation, not a word equation,
is always expected.
Balanced equations
It is essential that you are able to balance full equations, ionic equations and half equations.
Remember these rules when balancing equations. The rules apply to any equation, even the most
complicated looking one.
1.
Write down the formulae for the reactants and products. The formula is fixed and can
not be changed.
C3H8 + O2 →
CO2 + H2O
2. The only way you can balance an equation is to place numbers in front of the formulae
(you can not change the formula by changing the subscript numbers). You must place
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numbers in front of the formulae until there are the same number of atoms of an
element on the reactant side of the equation as there are on the product side of the
equation.
NO!
C3H8 + O3 →
C3O2
+
H 8O
YES!
C3H8 + 5O2 → 3CO2 + 4H2O
There are now 3 carbons, 8 hydrogens & 10 oxygens on each side.
3. You must also ensure that the charges balance.
H+ +
OH- →
H 2O
The positive and negative charges make an overall zero charge on the reactant side while the
products have no charge so the charges are balanced.
2Na+ +
SO42- →
Na2SO4
By placing a 2 in front of the sodium ion not only have we balanced the sodium but also the
charges – there are two positive and two negative charges on the reactant side resulting in an
overall zero charge and zero charge on the products side.
4. If required you then put state symbols in the balanced equation to show the state of the
reactants and products. Remember to think carefully; is the water produced a gas or a
liquid in your reaction?; Precipitates are solids; Is a gas given off?: Acids tend to be
dissolved in water therefore they are aqueous.
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous (dissolved in water)
MgCO3(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) +
CO2(g)
5. NOW CHECK – do all the elements balance, do all the charges balance, are the state
symbols correct.
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Practical techniques
Throughout the course you will be shown and have the opportunity to practise practical
techniques. You are required to know how to carry out these techniques and why you use them.
You may be asked about them in the ISA exam. Use the following Youtube clips to help you
better understand some of the processes you will learn – especially before an ISA exam. The
information presented below is not exhaustive and may be added to.
1. Go to www.youtube.com
2. In the search box put in the following key words/titles to bring up the appropriate clip
a) RSCteacherfellows then
 Recrystallisation
 Hot filtration
 Melting point determination
 Running an Infrared Spectrum
 Distillation
 Vacuum Filtration
 Thin Layer Chromatography
 Heating under reflux
 Weighing compounds using a balance
b) Preparing a standard solution
c) Pipetting Technique
d) Titration technique using a burette
e) Organic Chem: How to Flute filter paper
f) Recrystallization of an impure compound (note: they refer to a conical flask as an ergimyer
flask)
g) Reflux reactions
h) Distillation
i) Extraction
j) Calorimetry, heat of neutralization.avi
You may be asked as part of your exam (particularly the ISA exam) the reasons for carrying out
a particular practical technique. The following information will help but you will have to add to
this knowledge throughout the course.
Technique
Why it may be used
Filtration
To remove an insoluble impurity
or to collect a recrystallised product
or to collect a precipitate
or to separate a solid product from a solution.
Hot filtration
To remove an insoluble impurity from a sparingly soluble solute
or from a solute (in a solution) requiring recrystallization. It is
necessary to keep the solution hot to stop the product crystallising
out
Fluted filter paper
To increase surface area to allow a faster filtration
Recrystallisation
To purify the product / To remove a soluble impurity
Distillation
To remove / purify / separate a liquid
Fractional distillation To separate liquids with different boiling points
Reflux
Gives all reactants chance to react. Speeds up reactions without the
reactants and products escaping
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Practical Observations
It is important when making practical observations, or answering exam questions which ask for
observations that you are descriptive and precise. The following are key descriptive words and
phrases that you should use where appropriate.
a) Where there is the word ‘colour’ then insert the appropriate colour e.g. Blue solution
b) Where there is the word ‘specific’ then insert the appropriate word e.g. carbon dioxide
gas produced
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White precipitate produced
’colour’ precipitate produced
Clear, colourless solution
Clear, colourless liquid
‘Colour’ solution
Gas produced
Bubbles of gas produced
Colourless gas produced
‘Specific’ gas produced
Liquid condenses
No visible change
White solid produced
‘Colour’ solid produced
Increase / decrease in temperature observed
Fizzing / popping sound heard
Sharp / pungent smell detected
Vapour given off
Just saying Lime water goes cloudy is no longer enough detail, instead you would say a
white precipitate was produced.
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Practical Accuracy
In an experiment there is an experimental uncertainty (often called 'experimental error').
Experimental uncertainty arises because of:



Limits in the precision of the measuring apparatus.
Imperfections in the experimental procedure itself.
Judgements made by the operator.
Operator error
To improve accuracy by you, the operator:


always record results to the precision allowed by the apparatus. For example, if the
balance reads to 0.01g, write 6.78g as 6.78g - make sure you don’t round it up to 6.8g or
7g.
always record results the moment you take them e.g. write down the mass used when
next to the balance, not after you have returned to your desk.
When doing calculations do not round up numbers too early – if you do you may loose accuracy
(see also section on significant figures).
Apparatus Errors
You must be able to calculate the size of errors in practical work.
Percentage error
=
Margin of error
Quantity measured
x
100
Mass
1. Consider weighing 1g of solid. If you use a two decimal place balance, the mass recorded will
be to the nearest 0.01g. In this example, the % error will be:
0.01 (margin of error) x 100 = 1%
1 (quantity measured)
2. Consider weighing the same 1g of solid on a three decimal place balance. The mass recorded
will be to the nearest 0.001g, and so the % error will be:
0.001 x 100 = 0.1%
1
There is much less error involved in this procedure.
3. Consider weighing 10g of solid on the two decimal place balance. In this case the % error will
be:
0.01 x 100 = 0.1%
10
This error is less than weighing 1g on this balance
Choose the right balance for the amount of material to be weighed.
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Volume
4. Consider measuring 25cm3 in a 25cm3 measuring cylinder. The measurement will normally be to
the nearest 0.5cm3 (the accuracy will be quoted on the apparatus itself), so the % error will
be:
0.5 x 100 = 2.0%
25
5. Sometimes on equipment the accuracy is quoted as a ± a value e.g. on a biuret the accuracy is
given as ±0.05cm3 so if 25cm3 of solution was dispensed then the % error will be:
0.05 x 100 = 0.2%
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However if 2cm3 of solution was dispensed then the % error will be:
0.05 x 100 = 2.5%
2
If choosing equipment to measure a volume choose the correct equipment based on the
amount to be measured and the possible error.
Other equipment
The errors for other equipment can be calculated in a similar way.
Total apparatus error
To work out the total error attributed to the apparatus for a particular experiment, then add all
the separate equipment errors together.
For example, imagine a pupil doing an experiment where she measured out 1.245 g of a base,
made it up to 250 cm3 of solution in a volumetric flask, pipetted 25 cm3 of that solution into a
conical flask, and then found that it reacted with 23.30 cm 3 of acid in a titration using a
burette.
Balance
( 0.001 g)
100 x (0.001/1.245) = 0.08%
Pipette
( 0.1 cm3)
100 x (0.1/25)
= 0.40%
100 x (0.1/250)
= 0.04%
3
Volumetric flask ( 0.1 cm )
Burette
3
( 0.15 cm )
100 x (0.15/23.30) = 0.64%
Total apparatus error
= 1.16%
This means that the result of the experiment should be within 1.16% of the correct value.
When you design experiments, you should aim to ensure that the total apparatus error is
minimised by working on a suitable scale and with suitable apparatus. A very small titre for
example (e.g. 5 cm3) leads to a very large apparatus error for the burette (3%).
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Dr. mravetz
Significant figures
Counting the significant figures in a number
Read the number from left to right and count all the digits starting with the first digit that is
not zero. The examples below all have four significant figures:





0.09047
1.794
2.560 (because this number has a zero that is to the right of a decimal place and is
shown it is counted as a significant figure)
0.007503
2.085 x 105 (using scientific notation like this shows without ambiguity the number of
significant figures – if it was shown as 2085000 we would not know if this was 4,5,6
or 7 s.f.
Accuracy and significant figures:
1) Always work out formula masses to one decimal place if data is taken off of the periodic table.
If data is taken from a question then use the appropriate level of significant figures for the
data given.
2) Mole calculations should always be to three significant figures.
3) If a problem asks for an answer to a certain number of significant figures or to a
certain number of decimal places then you must do as the question asks. E.g.
a) If the answer is 5.67g but the question requires an answer to 1 decimal place then the
answer must be rounded up to 5.7g
b) If the answer is 52.63cm3 but the question requires an answer to 3 significant figures
then the answer must be rounded down to 52.6cm3.
4) General addition and subtraction: The value with the fewest decimal places (0.74 – 2 decimal
places) determines the number of significant figures in the answer. The answer can contain no
more decimal places than the least accurate measurement.
519.8754 - 0.74 + 5.337 = 524.4724 = 524.47 (2 decimal places)
Answer must be rounded to 524.47
5) General multiply and divide: The quantity with fewest significant figures determines the
number of significant figures in the answer.
e.g. If an object has a mass of 29.1143g (6 significant figures) and a volume of 25.0cm3 (3
significant figures) then its density is given by
29.1143 = 1.164572g/cm3 = 1.16g/cm3
25.0
Answer in 3 significant figures
NOTE: Round off numbers at the END of calculations so errors are not carried through.
.
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Dr. mravetz
Yields
1) Atom economy tells us in theory how many atoms must be wasted in a reaction or how many
atoms enter the desired product:
% atom economy = mass of desired product x 100%
Total mass of reactants
The mass is calculated from the balanced equation.
2) The yield tells us about the practical efficiency of the process:
Yield of a chemical reaction = The number of actual moles of a specified product x 100%
Theoretical maximum number of moles of the product
Or
=
actual yield in grams x 100%
Theoretical yield in grams
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Dr. mravetz
Hazards / precautions
Hazards
New international hazard symbols are coming into use. You must know these symbols.
SYMBOL (red diamond)
HAZARD
Caution – used for less serious health
hazards like skin irritation.
Flammable
Dangerous to the environment
Explosive
Oxidising
Longer term health hazards such as
carcinogenicity
Corrosive
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Dr. mravetz
Gas under pressure
Toxic
Precautions
In ISA exams in particular you may be asked about how to minimise risk to do with hazards.
When answering these sorts of questions you must be specific to the question. E.g if the
question asks ‘How can contact with the skin be minimised?’ then it is no use answering ‘by
washing hands’ because this is not a precaution – this is something you do after contact has been
made. The following table gives some precautions to be taken against hazards but it is by no
means exhaustive and you must continue to add to it as you gain experience in the laboratory.
Hazard
Chemical substance
Possible harm
Contact with the person
causes irritation, burns,
poisoning, death (dependent
on hazard symbols)
Breaking glass e.g. breakage,
putting bungs in test tubes,
putting pipette holders on
pipettes
Cuts
Bunsen burner, heating
mantle, hot equipment
Burns / fires
Bags / stools
Trip hazard – someone falls
over
Possible contact with
substance causing irritation,
burns, poisoning (dependent
on hazard symbols)
Chemical spills
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Dr. mravetz
Precaution to reduce risk
Use gloves
Place lids on containers
Mop up spillages
Wear safety glasses
Wear a mask
Wear safety glasses
Use appropriate apparatus
to hold equipment e.g. test
tube rack
Hold glassware close to
where the bung/holder is
being inserted
Tie hair back
Leave hot equipment to cool
Do not have flammable
substances nearby
Bags and stools under the
table out of the way
Keep tops on bottles when
not in use
Mop up spills straight away
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Dr. mravetz