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Examiner’s tips
At A2, you will go further and deeper into the study of chemistry – you will build on
the work done at AS. As at AS, the work at A2 is divided into units and modules.
Each unit corresponds to one of your examination papers. These tips have been
written to help you in your studies and have been divided into the modules that fit in
each unit. Use these tips to guide you – they will help you to know what to look for.
However, they are not intended as a comprehensive set of revision notes – they can
form a skeleton for your revision but you should refer to your textbook and the
Revision flashcards and Content checklist to complete your notes.
General guidance
There are a number of areas that often cause problems for students when
answering various examination questions. These tips should help you avoid such
problems and are essential to good examination technique.

Practise questions on past examination papers and check the corresponding
mark schemes. These can be an invaluable learning and revision resource.
However, don’t expect exactly the same questions to come up on your
examination paper – be prepared to adapt your knowledge to suit the
question.

Always read the question fully and carefully (at least twice!) before beginning
your answer. A common mistake is for candidates to incorrectly transfer a
number in the question, such as writing down 36 instead of 30.

Diagrams and sketch graphs can earn marks – often more easily and quickly
than written explanations – but they will only earn marks if they are carefully
drawn.
 If asked to draw or sketch a graph, always ensure you use a sensible
scale and label both axes with quantities and units. If plotting a graph,
use a pencil and draw small crosses or dots for the points.
 Diagrams must always be neat, clear and fully labelled.

Using bullet points in written explanations can sometimes help you
concentrate on the actual answer.

Each module of the A2 chemistry specification consists of a series of learning
outcomes – i.e. what you are supposed to know! It forms the basis of what
the examiner will ask you in the examination. Not surprisingly, it’s essential
that you are familiar with as many of these learning outcomes as possible
before entering the examination room.

At A2, the exams are synoptic with a likely overlap with the respective AS
unit. For example, the A2 Unit F324: Rings, polymers and analysis will have
questions relating to some of the basic organic material covered in the AS
F322 Unit: Chains, energy and resources. Similarly, the A2 F325 Unit:
Equilibria, energetics and elements will have questions relating to the Energy
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section of the AS Unit F322 as well as with the Electrons, bonding and
structure section of the AS Unit F321.

You will still need to know the work covered in AS Unit F321: Module 1 –
Atoms and reactions in order to carry out any appropriate calculations.

Remember, scientific words have specific meanings and these meanings
may differ to those used in everyday language – a particular language/format
is used in chemistry so that chemists know exactly what is meant by other
chemists when explaining certain concepts.
 Formal definitions have to be used. Most of these were covered during
the AS course, but key definitions are also found at A2. It is important
that you learn these definitions (highlighted in the unit/module section
below).

To help guide you through the A2 course, these tips have been organised
according to the relevant unit modules – with the modules further subdivided
into sections. This will enable you to dip in and out as you need to.

Remember, each tip is just a guide to what you might be asked – it won’t
contain all the information you’ll need but just some basic points to help you.
The actual learning is down to you. I can only point you in the right direction.
Calculations in chemistry
Some skills acquired at AS will be used throughout A2 and a number of marks in an
A2 chemistry paper will be given over to calculations.

You will need to remember what is meant by empirical formula and molecular
formula and how to calculate both of them from percentage by mass data.

The following relationships will feature throughout the A2 course.

The relationship between mol, mass and Molar mass, M, for all
substances.
Key fact: 1 mol = M in grams
Although there are many ways to work out calculations involving these
units, it’s a good idea to learn the equation for interconverting mol,
mass and M which is:
mass (g) = n (mol) × M (g mol–1)
Now you can rearrange the equation to find the term being asked for in
the question.
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
The relationship between mol and 24 dm3 for gases.
Key fact: 1 mol of any gas = 24 dm3 (24 000 cm3) at room temperature
and pressure
Learn the equation for interconverting mol, volume and 24 dm3 which
is:
volume (dm3) = n (mol) × 24 (dm3)
volume (cm3) = n (mol) × 24 000 (cm3)
Now you can rearrange the equation to find the term being asked for in
the question.

The relationship between mol and concentration for solutions.
Key fact: 1 mol dm–3 = 1 mol of substance dissolved in water to give
1000 cm3 of solution
Learn the equation for interconverting mol, concentration and volume
of solution in dm3 which is:
n (mol) = concentration (mol dm–3) × volume of solution (dm3)
Now you can rearrange the equation to find the term being asked for in
the question.
However, most volumes are given in cm3 which means the equation
becomes:
n (mol) = concentration (mol dm–3) × volume of solution (cm3)
1000

The big difference between AS and A2 is that any calculations involving these
relationships will be unstructured. In other words, the question will not be split
into subsections that guide you towards a final answer. Rather, you will be
given some basic information from which you will be expected to derive the
required answer. However, the general approach is still the same.

Step 1: work out how many moles of the first substance reacted. Do
this using one of the three formulae above.

Step 2: look at the balanced equation to see how many moles of the
other substance reacted.

Step 3: use one of the three formulae to calculate the mass/volume of
gas/concentration of solution of the second substance.
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Unit F324: Rings, polymers and analysis
Module 1 – Rings, acids and amines
Arenes

Arenes feature throughout organic chemistry.
 They have their own particular way of reacting due to their bonding.
 The delocalised ring of electrons is very stable and usually will not
react without the presence of a catalyst – often referred to as a
halogen carrier.

The benzene ring will undergo a mechanism known as electrophilic
substitution.
 You will need to describe this mechanism – curly arrows and all!
 You should be able to identify the electrophiles which take part in this
reaction such as NO2+ and X+ (X being a halogen).
 Each electrophile has its own particular catalyst – you will also need to
learn the role of the specific catalyst in this mechanism.

Phenol is placed in the arenes section of your A2 chemistry course.
 You need to learn the two reactions of the OH group in a phenol in the
specification – i.e. reaction with alkalis and alkali metals.
 You also need to learn how the OH group affects the ease with which
the benzene ring can undergo electrophilic substitution.
Carbonyl compounds

Carbonyl compounds are dominated by the C=O bond.
 Not all molecules with a C=O bond are carbonyls – only those in
which the carbon atom is bonded to another carbon (ketones) or to a
hydrogen (aldehydes).
 This means COOH groups (carboxylic acids), COCl groups (acyl
chlorides), COOR groups (esters) and CONH2 groups (amides) are
not carbonyl compounds

Both carbonyl homologous series (i.e. ketones and aldehydes) undergo
similar reactions for most of the time – learn the general case reactions
and learn the one or two which differ.

You will need to describe how ketones and aldehydes can be made from
different classes of alcohol (see AS Unit F322: Module 2). You also need
to know how to:
 oxidise aldehydes – not ketones.
 reduce both carbonyls back to the alcohols they originate from.
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
The mechanism for reduction is nucleophilic addition.
 This is another mechanism that will feature heavily during your A2
course – once again you need to learn how to use curly arrows and
dipoles.

Two special reactions of carbonyls include:
 2,4-dinitrophenylhydrazine (2,4-DNPH) to detect the presence of a
carbonyl group and to identify specific carbonyl molecules by
measuring the melting temperature of the solid product
 Tollens’ reagent to distinguish aldehydes from ketones – also known
as the silver mirror test.
Carboxylic acids and esters

Carboxylic acids can behave just like the acids you studied in AS Unit
F321: Module 1 - Atoms and reactions
 You will need to describe how they can be made from primary
alcohols (AS Unit F322: Module 2 - Alcohols, halogenoalkanes and
analysis).

Carboxylic acids and ester are interconvertable.
 You need to describe how to make esters from:
o acids and alcohols (AS Unit F322: Module 2 - Alcohols,
halogenoalkanes and analysis)
o acids and acid anhydrides.
 Esters are converted back to carboxylic acids/salts and alcohols by
hydrolysis – either in acidic or alkaline conditions.

You need to be aware of the role of fatty acids as a health issue.
Amines

Amines can be thought of as organic ammonia molecules due to the
important presence of the lone pair of electrons on the nitrogen atom.

You need to describe how both types of amine – aliphatic and aromatic –
can be made by a reduction reaction.
 Aliphatic amines are made by using different conditions to those used
to make aromatic amines.
 You need to describe how to convert aromatic amines into azo dyes
and the special conditions required.
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Module 2 – Polymers and synthesis
Amino acids and chirality

Amino acids feature heavily during your A2 chemistry course and you
must learn all about their important aspects including:
 their structure
 that they can behave as both carboxylic acids and amines, depending
upon whether their environment is acidic or alkaline.

Amino acids form polypeptides – proteins
 Polypeptides can be converted back to amino acids via hydrolysis.

You need to know how to spot chiral carbon atoms within structures and
thus optical isomers.
 You must be able to draw both non-superimposable mirror images.
 These diagrams must be in 3D.
Polyesters and polyamides

You must be able to show condensation polymerisation from given
monomers.
 It is often a good idea to draw more than one complete unit of a
polymer and to circle one complete unit.
 Check that all the atoms circled are equivalent to both the monomers
minus two hydrogen atoms and one oxygen atom.

Polyesters have an ester link between the monomers – e.g. Terylene,
Polylactic acid.
 Polyamides have an amide (peptide) link between the monomers –
e.g. Nylon, Kevlar.
 Both types of polymer can be converted back to monomers by
hydrolysis.

Sometimes you will be asked to predict the monomers which made up a
polymer.
 This could be applied to the addition polymers you covered in AS Unit
F322: Module 2 - Alcohols, halogenoalkanes and analysis.
Synthesis

Synthesis can involve any functional group from within the specification.
 It relies upon the candidate’s ability to convert from one functional
group to another.
 So you must have a good knowledge of all aspects of the organic
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chemistry covered during your A level course.

You must understand the problems of chirality when synthesising novel
pharmaceuticals and how pharmaceutical companies go about removing
the unwanted isomer.
Module 3 – Analysis
Chromatography

You will cover two types of chromatography:
 thin-layer chromatography (TLC)
 gas chromatography (GC).

You need to know the theory behind each process.
 You also need to know how to identify compounds using each
technique:
o TLC uses Rf values
o GC uses retention times – GC can be linked to a mass
spectrometer (MS) for a more powerful technique (MS was
covered in AS Unit F322: Module 2 - Alcohols,
halogenoalkanes and analysis).
Spectroscopy

This part of the course usually involves the analysis of spectra.
 You need to practise this by studying as many carbon-13 NMR
spectra and proton NMR spectra as possible.
 As well as identifying the compounds in question you may be asked
how you came to your conclusion – e.g. splitting patterns in proton
NMR.
 However, you need to remember that the compounds requiring
identification will be limited to those containing C, H, O, N and halogen
atoms.

Both types of NMR spectra can be combined with information from other
techniques such as infrared and mass spectra (see AS Unit F322: Module
2 - Alcohols, halogenoalkanes and analysis).
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Unit F325: Equilibria, energetics and elements
This module is a natural follow-on from your AS course Unit F322: Chains, energy
and resources, Module 3 – Energy (Section 3.1 Enthalpy changes and Section 3.2
Rates and equilibrium).
Module 1 – Rates, equilibrium and pH
How fast?
 During your AS course you learned about rates:
 how quickly a reaction reaches equilibrium based upon collision
theory
 how and why factors affect the rate in terms of particles
 how to draw Boltzmann distribution curves
 how these diagrams can be used to explain how a catalyst or a
temperature change alters the rate of a reaction.
 Now at A2, numbers become involved:
 rate equations need to be worked out
 orders determined
 rate constants (with correct units) need to be calculated.

This can be done either by looking at:
 concentration-time graphs and understanding the importance of a
half-life
 initial rate-concentration graphs
 the importance of a rate-determining step needs to be understood.
How far?

Although equilibrium at A2 is still based upon le Chatelier’s principle and
how factors affect the balance of a reaction – e.g. more reactants, less
products, etc., you must now be able to:
 calculate values for the equilibrium constant, Kc, including the units
 determine the effect of temperature change upon Kc.
Acids, bases and buffers

Here, there is some overlap with AS Unit F321: Module 1 - Atoms and
reactions, since key points still include the definition of acids as proton
donors and ionic equations of acid reactions. However, at A2 you will
need to be able to:
 conjugate acid-base pairs
 work out the difference between strong and weak acids.
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
Calculations will also feature heavily and could include:
 Ka and pKa of weak acids
 pH of strong acids, weak acids and strong bases.

You will need to explain what is meant by the term buffer. You will need to
know how to:
 make buffers
 explain how they work
 calculate the pH of a buffer solution.

You will need to interpret titration curves and their relationship to acid /
base strength and how this affects the choice of indicator used.

Finally, you may be asked about neutralisation.
 One of the few definitions you need to know at A2 is the enthalpy of
neutralisation.
 You will need to be able to calculate enthalpy changes from
experimental data using the Q = mcΔT equation (covered in AS Unit
F322: Module 2 - Alcohols, halogenoalkanes and analysis).
Module 2 – Energy
Lattice enthalpy

You will need to be able to explain what lattice enthalpy means and to
construct Born-Haber cycles based upon information given – state
symbols will be relevant here!
 You may be asked about some of the AS material covered in AS Unit
F322: Module 2 - Alcohols, halogenoalkanes and analysis including:
o Q = mcΔT
o standard enthalpy change of reaction
o standard enthalpy change of combustion
o standard enthalpy change of formation
o average bond enthalpy.

Energy cycles involving Hess’ law may also feature.

You need to understand new terms such as:
 enthalpy change of solution
 enthalpy change of hydration
 lattice enthalpy.
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Enthalpy and entropy

You must be able to:
 carry out simple entropy calculations
 understand the meaning of the term free energy change, ΔG, and the
equation ΔG = ΔH – TΔS
 understand the relationship between entropy and enthalpy.
Electrode potentials and fuel cells

You will revisit the idea of redox – first learnt in AS Unit F321: Module 1 Atoms and reactions. At A2 you should be able to use the terms:
 redox
 oxidation number
 half-reaction
 reducing agent
 oxidising agent appropriately.

A way to earn some marks is by knowing the definition of standard
electrode potential.

You will need to describe how standard electrode potentials can be
calculated against the standard hydrogen electrode – both for metals and
ions or pairs of ions.
 You will need to know how to use values of electrode potentials in
order to predict if reactions will occur.

It is important to know the changes that can happen within fuel cells – e.g.
in hydrogen-oxygen fuel cells.
 You must also be aware of any economic, political and environmental
issues.
Module 3 – Transition elements
Transition elements

You must be able to deduce the electron configurations of the transition
metals and their ions.
 You may be required to work out electron configurations of unusual
ions based upon this knowledge.
 You must also know the four key properties of transition elements:
o good catalysts
o variable oxidation states
o formation of complex ions
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
o formation of coloured ions.
It is always a good idea to be able to quote an example for each
property.

You need to describe about the formation and colour of the hydroxide
precipitates of:
 Fe2+
 Fe3+
 Co2+
 Cu2+

Ligands play an important part in transition element chemistry. You need
to describe:
 how ligands bond to ions
 the shapes of the complexes formed
 the isomerism (cis/trans and optical) shown.

Ligand substitution is also important and you will be required to:
 calculate and use the stability constants, Kstab, of complexes
 know the colour changes associated with ligand substitution listed in
the specification.

You may also encounter redox titrations – these are similar to the acid
base titrations you met in AS Unit F321: Module 1 - Atoms and reactions.
However, unlike at AS:
 the ratios of reactants you encounter at A2 may be in the order of 5:1
or 2:5 – very different from the 1:1 ratio or 1:2 ratio seen at AS!
 you will be expected to carry out the calculations without any guidance
from the exam paper.
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