Download AQA GCSE Chemistry My Revision Notes

Question 1
Group 1 elements burn vigorously when heated in oxygen.
(a) Complete these diagrams to show the electronic structures of sodium and
oxygen atoms.
(2 marks)
(b) Write the word equation that describes the reaction between sodium and
oxygen.
(1 mark)
(c) Write the balanced equation for this reaction, including the state symbols.
(3 marks)
(d) Why are the elements in group 0 unreactive?
(1 mark)
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Question 2
When limestone is heated to make cement it first reacts to produce lime (calcium
oxide).
(a) Write a word equation using chemical names for what happens when limestone
is heated.
(1 mark)
(b) Write the chemical formula for:
(i)
limestone
(1 mark)
(ii)
lime
(1 mark)
(c) Write a balanced equation with state symbols for what happens when limestone
is heated.
(2 marks)
Water reacts with lime to form slaked lime (calcium hydroxide).
(d) Write a word equation for this reaction using chemical names.
(1 mark)
(e) Write a balanced equation with state symbols for this reaction.
(3 marks)
(f) Farmers use slaked lime for liming the soil. Why is it necessary to lime some
soils?
(1 mark)
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Question 3
Copper can be obtained from solutions of copper salts by electrolysis or by
displacement using scrap iron. It can also be extracted by phytomining.
(a) Draw an arrow on the following reactivity series (reactivity decreases down the
list) to show where copper should be placed.
(1 mark)
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
(b) Write a word equation for the displacement of copper from copper sulfate
solution by iron.
(1 mark)
(c) Write a balanced equation with state symbols for this reaction.
(3 marks)
(d) Explain why copper is produced at the negative electrode during electrolysis.
(2 marks)
(e) What is phytomining?
(2 marks)
(f) Predict the method of extraction used to obtain calcium from its ore and explain
your answer.
(2 marks)
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Question 4
Crude oil is a mixture of compounds, mainly hydrocarbons.
(a) What is a hydrocarbon?
(b) The table gives the boiling points of four hydrocarbons.
Hydrocarbon
P
Q
R
S
(1 mark)
Boiling point in °C
174
–161
125
–42
Which of these hydrocarbons are gases at room temperature (20°C)? (1 mark)
(c) Which of these hydrocarbons has the largest molecules?
(1 mark)
(d) Fractional distillation can be used to separate crude oil into fractions. Describe
how this process works.
(3 marks)
(e) Draw the structure of ethane, C2H6, showing all the bonds.
(1 mark)
(f) Write a balanced equation for the complete combustion of ethane. (3 marks)
(g) The use of hydrocarbons as fuels can lead to acid rain. Explain how this arises.
(3 marks)
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Question 5
The cracking of large molecules involves their thermal decomposition.
The diagram shows an apparatus that can be used to crack hydrocarbons in the
laboratory.
(a) What is thermal decomposition?
(2 marks)
(b) Why is the porous pot included in the apparatus?
(2 marks)
(c) Complete the equation below for the cracking of the molecule C20H42. (1 mark)
C20H42  C3H6 + _____________________
(d) What chemical test would you use to show that the gas, propene, was an alkene?
(3 marks)
(e) Draw the structure of the propene (C3H6) molecule, showing all the bonds.
(2 marks)
(f) Explain what is meant by polymerisation.
(2 marks)
(g) Use a diagram to show the formation of poly(propene).
(3 marks)
Crude oil is used to produce many useful fuels, but oil reserves are being used up.
One way to conserve crude oil reserves would be to increase the production of biofuels.
Ethanol can be produced for use as a bio-fuel. Cars can be powered by ethanol or
ethanol–petrol mixtures.
Sugar cane can be fermented to give a mixture of water (boiling point 100°C) and
ethanol (boiling point 78°C).
The cost of producing ethanol by fermentation is very much higher than the
production cost of petrol. It costs less to produce ethanol from crude oil (alkanes). In
the production, the vapour of an alkane is passed over a hot catalyst to produce
ethene. Ethene is then converted into ethanol.
(h) Describe how ethanol, C2H5OH, can be produced from ethene.
(2 marks)
(i) Ethanol can be made using either sugar or alkanes as the starting material.
Evaluate the advantages and disadvantages of using these two starting materials
to produce ethanol.
(4 marks)
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Question 6
(a) Describe why vegetable oils are an important part of our diet.
(2 marks)
Some crisps are claimed to be healthier because they are cooked in sunflower oil.
A student found the following information about three oils that are used to make
crisps. The iodine value is the mass (in grams) of iodine that reacts with 100 g of oil.
Plant oils with lower iodine values are harder and are less unsaturated.
Oil
Olive
Rapeseed
Sunflower
Iodine value
82
113
133
Oils are thought to be healthier if they are high in polyunsaturated fat.
(b) What is an unsaturated vegetable oil?
(1 mark)
(c) Iodine solution reacts in the same way as bromine water. What would you see as
the iodine reacts with each of the oils?
(1 mark)
(d) Use the data in the table to decide which oil should be healthiest. Explain your
answer by comparing this oil with other oils.
(2 marks)
(e) Sunflower oil is a liquid and can be used to make margarine. Explain how it can
be processed to make it suitable for such use.
(5 marks)
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Question 7
(a) What are the names of the main two gases in our atmosphere today? (1 mark)
Over 3 billion years ago, our planet’s atmosphere was mainly water vapour, carbon
dioxide, methane and ammonia.
(b) Why is there now less water vapour in the atmosphere?
(2 marks)
For the last 200 million years the amount of carbon dioxide in the atmosphere has
remained almost the same.
(c) Describe the natural processes that remove carbon dioxide from the
atmosphere.
(4 marks)
To gain full marks in this question you need to use continuous prose. You will
be marked on your ability to use good English, organise information clearly and
use specialist vocabulary where appropriate.
The diagram shows the Peru–Chile trench, which runs down the west coast of South
America. It is the boundary between two tectonic plates that are moving towards
each other.
(d) What causes the tectonic plates to move?
(e) How are earthquakes caused?
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(2 marks)
(2 marks)
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Question 8
When sodium reacts with chlorine, sodium ions and chloride ions are formed.
(a) Explain how a sodium atom changes into a sodium ion.
(2 marks)
(b) Explain how a chlorine atom changes into a chloride ion.
(2 marks)
Rubidium (Rb) is in the same group of the periodic table as sodium. Rubidium
reacts with chlorine to make rubidium chloride.
(c) Predict the formula of rubidium chloride.
(1 mark)
(d) Explain why the reaction of rubidium with chlorine is similar to the reaction of
sodium with chlorine.
(2 marks)
(e) What holds the sodium and chloride ions together in a crystal of sodium
chloride?
(2 marks)
(f) Sodium and rubidium are metals. Describe the structure and bonding in metals.
A diagram may be used if you wish.
(4 marks)
(g) Explain how the structure and bonding of rubidium allow it to conduct
electricity.
(2 marks)
(h) Nitrogen and hydrogen react together to form ammonia, NH3. What type of
bonding occurs in this compound?
(1 mark)
(i) Use a dot-and-cross diagram to show the bonding between nitrogen and
hydrogen in ammonia.
(2 marks)
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Question 9
The diagram shows the structure of diamond.
(a) Explain why the bonding in diamond gives it a high melting point.
(4 marks)
(b) Complete the following diagram to show the electron structure of a hydrogen
chloride molecule. Use dots and crosses to represent electrons.
(2 marks)
(c) Explain why hydrogen chloride is a gas at room temperature.
(2 marks)
The diagram represents the structure of graphite.
(d) Graphite is soft, slippery and conducts electricity. Explain why the structure
and bonding in graphite give it these properties.
(5 marks)
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The diagram shows the giant structure of sodium chloride, which has a melting
point of 801°C.
(e) Explain why the bonding in sodium chloride gives it a high melting point.
(2 marks)
(f) Explain why solid sodium chloride will not conduct electricity but when molten
it will.
(3 marks)
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Question 10
A 69 g sample of a carbohydrate was found to contain 42 g of carbon and 3.0 g of
hydrogen.
(a) Calculate its empirical formula.
(4 marks)
Salicylic acid (C7H6O3) can be used to produce aspirin according to the equation:
C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH
salicylic acid
aspirin
In an experiment a student used 5.0 g of salicylic acid to prepare a sample of aspirin.
(b) What is the maximum mass of aspirin the student could have made? (4 marks)
(c) The student actually produced 5.2 g of dry, purified aspirin. What was the
yield?
(2 marks)
(d) Give three reasons that could have reduced the yield in this reaction. (3 marks)
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Question 11
Some students did a series of experiments measuring the rates of the reaction
between magnesium and nitric acid.
(a) In terms of particles, when will a reaction occur?
(2 marks)
(b) Write the equation for the reaction between magnesium and nitric acid, using
the appropriate state symbols.
(3 marks)
(c) After some preliminary experiments the students decided that temperature
would be a difficult factor to control. Suggest why this might be.
(2 marks)
(d) Why does a steep line on these rate graphs show the reaction rate is fast?
(2 marks)
(e) Explain why the concentrated solution of acid reacted faster and produced
more product than the dilute solution.
(3 marks)
(f) Why does increasing the temperature of a reaction increase the rate?(3 marks)
The students had used manganese(IV) oxide as a catalyst in a different experiment
and did some trials with it in this reaction (between magnesium and nitric acid).
They found it had no effect on the reaction.
(g) What effect were the students looking for?
(1 mark)
(h) Why did manganese(IV) oxide not work as a catalyst in this reaction? (1 mark)
(i) Why are catalysts important in industrial processes?
(1 mark)
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Question 12
Some hydrated magnesium sulfate (MgSO4.7H2O) was heated in a crucible until
there was no further change in mass. The following reaction had occurred:
MgSO4.7H2O(s)  MgSO4(s) + 7H2O(l)
(a) Why was it heated until there was no further change in mass?
(1 mark)
(b) When some drops of water were put onto the cooled anhydrous product, the
solid became hot and some water turned into steam. What does this tell you
about this reaction?
(2 marks)
(c) The reaction is better written like this:
MgSO4 .7H 2O(s) É MgSO4 (s)  7H 2O(l)
What can you now say about the forward reaction?
(2 marks)
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Question 13
(a) Copper sulfate crystals can be prepared by reacting solid copper(II) oxide with
an acid. Which acid would be used?
(1 mark)
(b) Why would excess copper(II) oxide be used?
(1 mark)
(c) Suggest how you would remove excess copper oxide when the reaction is
complete.
(1 mark)
(d) What process would you use to produce solid copper sulfate crystals from the
solution?
(1 mark)
(e) What is the name given to a reaction in which an acid reacts with a base to
make a salt?
(1 mark)
(f) How would the pH change as the copper(II) oxide reacted with the sulfuric acid?
(1 mark)
(g) Insoluble salts can be made by precipitation. How would the addition of
limewater to industrial effluent remove dissolved lead (Pb2+(aq))? (2 marks)
(h) Write a balanced chemical equation for the limewater reaction in part (g).
(4 marks)
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Question 14
In an industrial electrolytic process electricity is passed through a solution of sodium
chloride in water.
(a) Chlorine gas is produced during the electrolysis. Complete the half-equation
that describes its formation.
(2 marks)
_______  Cl2 + _______e–
(b) The solution left in the cell is alkaline. Which ion makes the solution alkaline?
(1 mark)
(c) What is the substance (labelled A) that is formed in solution in the cell?
(1 mark)
(d) Hydrogen is also produced in the cell. Hydrogen ions gain electrons in this
process. What is the name of this type of reaction?
(1 mark)
Another industrial application of electrolysis is the production of aluminium from
molten aluminium oxide.
(e) Write the half-equation, including state symbols, to show the formation of
aluminium at the cathode.
(2 marks)
(f) Explain why the carbon anodes have to be replaced.
(2 marks)
(g) Why is aluminium oxide dissolved in cryolite?
(2 marks)
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Question 15
The table below is part of the periodic table compiled by John Newlands in 1864. He
arranged the elements in order of their relative atomic masses and found a repeating
pattern. He arranged the elements into seven groups, every eighth element having
similar properties.
1
H
F
Cl
2
Li
Na
K
3
Be
Mg
Ca
4
B
Al
5
C
Si
6
N
P
7
O
S
(a) Suggest one reason why this part of Newlands’ table is different from the
modern one.
(1 mark)
In 1869 Dimitri Mendeleev arranged the elements by putting them in order of their
atomic weights. When he put them into a table he ensured that elements with similar
properties were in columns.
(b) What two things did Mendeleev do to ensure that elements in the same column
had similar properties?
(2 marks)
(c) Explain how the periodic table is now based on atomic structure.
(3 marks)
(d) Why it is not possible to find a new element that would fit between carbon and
nitrogen?
(1 mark)
(e) Explain, in terms of electrons, why rubidium is more reactive than sodium.
(4 marks)
The table shows how group 7 elements react with iron in the form of iron wool.
Element
Fluorine
Chlorine
Bromine
Iodine
Reaction with iron wool
Description
Iron burns without being
heated
Heated iron glows brightly
Heated iron glows
Iron glows if heated
strongly
Product
Iron fluoride
Iron chloride
Iron bromide
Iron iodide
(f) Explain why group 7 elements react in a similar way with iron.
(2 marks)
(g) Explain the difference between the reactions of fluorine and iodine with iron.
(2 marks)
(h) Explain why group 0 elements are found as single atoms.
(2 marks)
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Question 16
In some parts of the country the water supplied to homes is hard water.
(a) What is hard water?
(2 marks)
(b) Give the names and formulae of the two ions that can make water hard.
(4 marks)
(c) There are some advantages of drinking hard water. Give one of them.
(1 mark)
(d) What happens if you use temporarily hard water in a kettle?
(2 marks)
(e) Explain how an ion-exchange column softens hard water.
(2 marks)
(f) Another way of softening hard water is to use sodium carbonate. Explain how
and include a chemical equation in your answer.
(4 marks)
Water of the correct quality is essential for life. In the UK water drawn from rivers
or reservoirs is treated before being pumped into homes.
(g) Explain the purpose of the filtration and chlorination processes that form part
of that treatment.
(2 marks)
(h) Despite the rigorous treatment of drinking water some people prefer the taste
and quality of filtered water. What three materials are used in these water
filters to remove the dissolved substances?
(3 marks)
(i) Drinking water can also be produced using distillation but this is expensive.
Explain why.
(1 mark)
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Question 17
(a) Explain why this diagram represents an exothermic reaction.
(2 marks)
(b) The reaction between methane and oxygen is exothermic. Write the balanced
equation for this reaction, including state symbols.
(3 marks)
(c) Explain, in terms of breaking and making bonds, why the burning of methane is
exothermic.
(3 marks)
(d) You know that a catalyst speeds up a reaction. Explain, in terms of the reaction
and energy, how it does this.
(2 marks)
(e) The diagram shows the energy levels for a particular reaction. Complete it by
drawing a line that you can then label to show the activation energy. (2 marks)
(f) Hydrogen and nitrogen react to make ammonia according to the equation:
3H2 + N2 → 2NH3
Using the data in the box, calculate the overall energy change for this reaction
and state if it is exothermic or endothermic.
(5 marks)
Bond
H–H
N≡N
H–N
Bond energy in kJ/mol
436
944
388
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Question 18
A school chemistry technician was tidying up in the outside chemical store. Four
bottles of chemicals were found where the labels were unclear. The technician
thought they were potassium carbonate, potassium chloride, potassium sulfate and
aluminium sulfate.
The following reagents were readily available:
 barium chloride solution acidified with dilute hydrochloric acid
 dilute hydrochloric acid
 silver nitrate solution acidified with dilute nitric acid
 sodium hydroxide solution.
The technician made up aqueous solutions of the unknown compounds and did some
tests to confirm their identity.
Describe the tests you would do to show that these chemicals are correctly named.
In each case give the reagent(s) you would use and then what you would see.
(a) The test and result for potassium ions.
(2 marks)
(b) The test and result for aluminium ions.
(3 marks)
(c) The test and result for carbonate ions.
(2 marks)
(d) The test and result for chloride ions.
(2 marks)
(e) The test and result for sulfate ions.
(2 marks)
(f) How would a flame test distinguish the aluminium compound from the others?
(1 mark)
The technician also found a large flask of hydrochloric acid, but the concentration
label had disintegrated.
25.0 cm3 of the hydrochloric acid were titrated against 0.4 mol/dm3 sodium
hydroxide solution. The average volume of hydroxide used was 24.0 cm3.
(g) Describe how the titration would be carried out.
(4 marks)
(h) Complete the equation for this reaction.
(2 marks)
NaOH + HCl → ________ + ________
(i) Calculate the concentration in moles per cubic decimetre of the hydrochloric
acid.
(2 marks)
1 mole of sodium hydroxide reacts completely with 1 mole of hydrochloric acid.
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Question 19
Nitrogen and hydrogen are reacted together in the Haber process to make ammonia.
The equation for the reaction is:
N 2 (g)  3H 2 (g) É 2NH 3 (g)
(a) What is the source of the nitrogen?
(1 mark)
(b) Explain why increasing the pressure increases the chance of reaction between
the nitrogen and hydrogen molecules.
(1 mark)
The graph shows how the percentage yield of ammonia depends on the temperature
and pressure inside the reaction vessel.
(c) Use your knowledge of the Haber process and the information on the graph to
describe the conditions used to increase the rate of reaction.
(4 marks)
(d) What is the percentage yield of ammonia produced at a temperature of 300°C
and a pressure of 100 atmospheres?
(1 mark)
(e) Describe and explain what changes should be made to the temperature and
pressure to increase the percentage yield of ammonia.
(5 marks)
(f) Why are the conditions of temperature and pressure which give the maximum
yield of ammonia not used in industry?
(2 marks)
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Question 20
Alcohols are a homologous series. Here are the first four:
(a) What is the general formula for the alcohols?
(1 mark)
(b) These four alcohols can be used as fuels. Write the chemical equation for the
complete combustion of ethanol, including state symbols.
(3 marks)
(c) Ethanol is used as a fuel in a wide range of applications, from food heating
burners to camping stoves. Give three reasons why ethanol is such a useful fuel.
(3 marks)
Alcohols oxidise to form carboxylic acids. For example, ethanol forms ethanoic acid.
(d) Carboxylic acids are weak acids. Why are they ‘weak’?
(2 marks)
(e) How does the pH of a weak acid such as ethanoic acid compare with the pH of a
strong acid such as nitric acid?
(1 mark)
Alcohols react with carboxylic acids to form esters. This ester is the product of
reacting ethanol with ethanoic acid.
(f) Give the name of this ester.
(1 mark)
(g) Esters are volatile compounds and have distinctive smells. What does ‘volatile’
mean?
(1 mark)
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Answer 1
(a)
It is not essential to pair up the electrons but it really helps you to count the
correct number and the examiner will be impressed by the neatness of your
answer.
You can use either crosses or dots for electrons, but in each diagram you have
to use all the same.
(b) sodium + oxygen → sodium oxide 
The question asks for the word equation, so do not use any symbols.
(c) 4Na(s) + O2(g) → 2Na2O(s) 
The 3 marks are allocated thus:

1 for the correct formulae, so pay attention to knowing how to generate the
formulae of compounds and knowing the elements that are diatomic (H2, N2,
O2, F2, Cl2, Br2, I2, At2)

1 for correctly balancing the equation

1 for using correct state symbols
(d) The elements in group 0 are unreactive because they have a full outer shell of
electrons. 
At GCSE it is easiest to think of elements reacting in order to gain full outer
shells.
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Answer 2
(a) calcium carbonate  calcium oxide + carbon dioxide 
It is essential that you use the chemical names for all the substances in a word
equation. Even for carbon dioxide, do not be tempted to use its formula, even
though you may say it in your head as you are writing the word equation.
(b) (i) Limestone: CaCO3. 
(ii) Lime: CaO. 
Writing these chemical formulae will help you with writing the chemical equation.
Make sure your symbols are clearly the right style, i.e. upper case, lower case
and subscript as appropriate. CaCO3, not CaCO3 or CaCo3.
(c) CaCO3(s)  CaO(s) + CO2(g) 
The 2 marks here are for the correct formulae and state symbols. It would
probably be difficult to balance the equation if you had incorrect formulae from
part (b).
(d) calcium oxide + water  calcium hydroxide 
Do not be put off by the use of the name ‘slaked lime’ if you have not seen it
before. Just read the question carefully.
(e) CaO(s) + H2O(l)  Ca(OH)2(s) 
The 3 marks are allocated thus:

1 for the correct formulae

1 for correctly balancing the equation

1 for using correct state symbols (note that water is a liquid (l); remember that
(aq) means dissolved in water)
(f) Farmers use slaked lime to reduce the acidity/increase the pH of the soil. 
You may not have been taught this but you should know that calcium hydroxide
is alkaline (high pH).
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Answer 3
(a) sodium
calcium
magnesium
aluminium
carbon
zinc
iron
 copper is here 
Copper has to be less reactive than iron in order for it to be displaced by iron. It
therefore appears below iron in the reactivity series.
(b) copper sulfate + iron  copper + iron sulfate 
(c) CuSO4(aq) + Fe(s)  Cu(s) + FeSO4(aq) 
You have not been given any formulae in this question. It is therefore vital that
you either know the formulae of compounds you have come across or that you
can work them out from the charges on ions found on the datasheet provided in
the exam.
2 marks are awarded for the correct formulae (right-hand side and left-hand side
of the equation) and 1 mark is for using the correct state symbols.
(d) Copper forms Cu2+/positive ions.  Positive ions move towards the negative
electrode during electrolysis. 
‘Explain’ in a chemistry question can be thought of as ‘given reasons why…’.
These reasons can be very short sentences or bullet points. You should not use
up space or time in repeating the question.
(e) Phytomining uses plants to absorb metal compounds.  The plants are then burned to
produce ash that contains the metal compounds. 
This is a question that requires a straight quote from the specification for full
marks. Learn such definitions.
(f) Electrolysis.  Because calcium is very reactive. 
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Answer 4
(a) A hydrocarbon is a compound made up of hydrogen and carbon only. 
Learn this definition and remember the ‘only’.
(b) The gases are Q  and S .
A substance is a gas when it is at or above its boiling point.
(c) P has the largest molecules.  It has the highest boiling point.
(d) Fractional distillation works by:

evaporating the oil 

allowing it to condense 

at a number of different temperatures 
You will find this in the specification. Simple statements of fact are all that the
examiner requires of you.
(e)
Draw all structures carefully, making sure the bonds are accurately between the
relevant atoms.
(f) C2H6(g) + 3½O2(g)  2CO2(g) + 3H2O(g) 
or
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g) 
The 3 marks are allocated thus:

1 for the correct formulae

1 for correctly balancing the equation

1 for using correct state symbols (note that here water is a gas (g); the
reaction is hot enough to make steam)
(g) Hydrocarbons contain sulfur (as an impurity).  The sulfur burns (along with the
hydrocarbons) to form sulfur dioxide.  The sulfur dioxide causes acid rain. 
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Answer 5
(a) The breaking down of a molecule  using heat .
(b) It is a catalyst  and speeds up the reaction .
(c) C20H42  C3H6 + C17H36 
(d) Use bromine water.  It would change from orange  to colourless .
Always note both the original and final colours when describing colour changes.
‘Clear’ would not score a mark. Remember, water is clear and colourless; copper
sulfate solution is clear and blue.
(e)
Draw all structures carefully, making sure the bonds are accurately between the
relevant atoms and double bonds are clearly two lines.
(f) Many small molecules (monomers)  join together to form very large molecules .
(g)
The marks are for:

correct propene structure (as here or in part (e))

correctly placed ‘n’ on both sides

brackets around the two-carbon unit, with CH3 on one of the carbons and two
bonds extending through the brackets
(h) Ethene is reacted with steam  in the presence of a catalyst .
(i)
Ethanol from sugar
Advantage
Conserves crude oil
reserves
Uses renewable resources
Ethanol from alkanes
Cheaper than ethanol
from sugar
Pure product
Disadvantage
Have to separate the
ethanol from water —
uses energy
Land used to grow sugar
cannot be used to grow
food
Have to use energy to
crack the alkanes
Ethene has to be further
reacted to produce
ethanol

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An evaluation question is best tackled by using a table. Look at the question;
there are two methods and you have to evaluate the advantages and
disadvantages of them both. That makes a table with four sections and there are
4 marks available for your answer. A valid comment in each section will score
maximum marks. Make sure you do not use the same point twice — for example
ethanol from sugar conserves crude oil (advantage) is the same as ethanol from
alkanes uses up crude oil (disadvantage).
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Answer 6
(a) They provide energy  and nutrients .
(b) One that contains double carbon–carbon (C=C) bonds. 
(c) It will lose its colour. 
You have not been told what colour iodine solution is, so do not guess. You do
know that: bromine reacts with C=C bonds in the test for unsaturation; iodine is
in the same group (group 7); and elements in the same group have similar
chemical reactions.
(d) Sunflower oil because it has the highest iodine value , which indicates that it is
more unsaturated than the other two oils .
(e) Unsuitable because it will be too soft/liquid at room temperature (an oil, not a fat) .
Process: react with hydrogen  at about 60C  with a nickel catalyst . Suitable now
because its melting point is higher, so it is harder. 
This question is worth 5 marks; make sure you make five valid points, answering
each part of the question in turn.
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Answer 7
(a) Nitrogen and oxygen 
You are asked for the names, do not give the formulae or chemical symbols.
(b) The water vapour cooled  and condensed to form the oceans .
(c) Using continuous prose and stating at least two ideas will score 1 mark. This is the
‘good English’ mark. Any three from this list (still working in prose) score 1 mark
each:

Plants take in carbon dioxide.

Carbon dioxide is locked up in fossil fuels/coal/oil etc.

Oceans remove carbon dioxide by reacting with it.

The reaction produces carbonates/hydrogencarbonates.

Carbonates form sedimentary rocks/are used to make shells.
The front page of the exam paper will tell you for which question you need to use
continuous prose. You will be marked on your ability to use good English,
organise information clearly and use specialist vocabulary where appropriate.
You can still think in terms of making 3 valid points; you just have to put them in
linked sentences, remembering to use ‘specialist vocabulary’ such as ‘reaction’,
‘carbonates’ and sedimentary rocks’. For example: ‘Plants absorb carbon dioxide
from the atmosphere, oceans also remove carbon dioxide by reacting with it.
This reaction produces carbonates, which form sedimentary rocks.’
(d) Convection currents within the Earth’s mantle  driven by heat released by natural
radioactive processes .
(e) By sudden and disastrous movements of tectonic plates  at the boundaries between
tectonic plates .
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Answer 8
(a) It loses its one  outer electron .
(b) It gains one  outer electron .
(c) RbCl 
Make sure your symbols are clear and unambiguous, e.g. the ‘l’ in Cl is a straight
line and not even hinting at being a ‘C’ or a capital ‘L’.
(d) Rubidium and sodium both have one electron  in their outer shells/highest energy
level .
You can use ‘electron shell’ or ‘energy level’ — whichever you have been taught
and use.
(e) An electrostatic force  of attraction  (between oppositely charged ions).
An ionic bond is ‘an omnidirectional force of attraction between oppositely
charged ions’. If you use this description properly you will score maximum
marks. There are no marks for ‘omnidirectional’ but it will impress your examiner.
(f) Metals consist of a giant structure  of positive ions  with electrons between the
ions  holding them together by strong electrostatic attractions .
A diagram such as this with the ‘sea’ of delocalised electrons and the positive
ions correctly labelled will score two of the marks.
(g) The delocalised electrons  are free to move .
(h) Covalent bonding 
(i)
1 mark is for a pair of electrons between each N and H, and 1 mark for the nonbonding pair of electrons. You can draw these diagrams with or without the
circles to represent the outer electron shells of the atoms.
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Answer 9
(a) There are a large number of strong  covalent bonds  between the atoms , which
require much energy  to break.
(b)
1 mark is for a pair of electrons between the H and Cl, 1 mark is for the other
three pairs of electrons.
It is not essential to pair up electrons in diagrams, but it represents how
electrons behave (AS chemistry). It also helps you to get the correct number in
each shell and make the diagram clearer for the examiner to mark.
(c) The forces between the molecules/intermolecular forces  are weak  (and require
little energy to be overcome).
You must be careful to clearly distinguish between chemical bonds (within simple
molecules or giant structures) and intermolecular forces of attraction. It helps to
refer to chemical bonds being broken but intermolecular forces being overcome.
(d) Any five of the following ideas will score 5 marks:

The atoms are in layers.

There are weak forces of attraction between the layers.

The layers can slide over each other (so graphite is slippery).

Each carbon atom forms three bonds.

Each carbon atom has one electron not used in bonding.

This electron is delocalised/free to move.

Electrons carry current (so graphite conducts electricity).
Any reference here to ionic bonding will reduce your score to a maximum of
4 marks.
When answering a question with a number of ideas in it (soft and slippery,
conducts electricity, structure, bonding) you must be careful to make a point
against each one:

soft and slippery – layers slide

conducts electricity – electrons are delocalised

structure — layers

bonding — three bonds per atom
(e) Strong forces between the ions  require much energy  to break them.
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Any mention of atoms in an ionic question will lose at least 1 mark, if not all the
marks!
(f) In solid sodium chloride the ions are vibrating about fixed positions ; they are not
able to move towards the electrodes. 
In molten sodium chloride the ions are free to move/mobile. 
Conduction of electricity can only happen when charged particles (electrons or
ions) can move towards electrodes. Be careful: ionic compounds conduct
electricity because the ions can move, it is not to do with electrons, so do not
mention them!
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Answer 10
(a)
Element symbol
Mass
Divide by relative mass
Ratio
Smallest whole ratio
Formula
C
42
42/12
3.5
7
C7H6O3
H
3
3/1
3.0
6
O
24
24/16
1.5
3
Use a table here and you will get full marks without much thought.
1 mark is for working out the mass of oxygen (it is the difference between the
sum of carbon and hydrogen and the sample mass).
1 mark is for dividing by the relative masses.
1 mark is for finding the smallest whole ratio; here by multiplying by 2 (often you
need to divide by the smallest number, but that does not work every time).
The final mark is for writing the formula — forget this and you drop the mark.
(b) formula mass of salicylic acid = 138 
formula mass of aspirin = 180 
maximum mass of aspirin 
5 g  180 g mol1
138 g mol1

= 6.5 g 
Alternatively:
138 g → 180 g
1
180
5
180
138
138
5g
= 6.5 g 
(c) yield 
5.2 g
 100% 
6.5 g
= 80% 
Make sure that your answers to numerical questions are clear and you let the
examiner know what you are working out at each stage. It is very difficult to
award marks to a disordered jumble of numbers and symbols! Try to make your
answer look like this one.
(d) 1
2
3
The reaction may be reversible/not go to completion. 
Some produce can be lost when it is separated from the reaction mixture, for
example when filtered. 
Some of the reactants may react in ways different from the expected reaction. 
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It is useful to you and the examiner to have such answers divided into sections.
The question asks for ‘three reasons’ so number your answers 1, 2 and 3 and
you will know when you have finished!
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Answer 11
(a) Chemical reactions can only occur when reacting particles collide  with each other
and with sufficient energy .
(b) Mg(s) + 2HNO3(aq) → Mg(NO3)2(aq) + H2(g) 
The 3 marks are allocated as follows:

1 for the correct formulae

1 for correctly balancing the equation

1 for using correct state symbols
(c) The reaction is exothermic  so it will generate heat and increase temperature as the
reaction proceeds .
(d) rate of reaction 
amount of product formed

time
This is the gradient of the line on such graphs. 
You may be tempted to use lots of words to explain this straightforward
relationship but it is best to keep it simple — waffle hides and sometimes loses
marks.
(e) Increasing the concentration of reactants in solution increases the frequency of
collision  hence the rate increases .
More product was formed because a concentrated solution has more chemical/a
greater amount of chemical in the same volume available to react. 
(f) Increasing the temperature increases the speed of the reacting particles  so that they
collide more frequently  and more energetically .
(g) An increase in the rate of reaction/faster bubbling. 
(h) Different reactions need different catalysts. 
(i) They reduce costs. 
Rate questions require very simple answers — you can quote the specification
and be assured of maximum marks.
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Answer 12
(a) To ensure the reaction had finished/all the water was driven off. 
(b) The reaction gives out heat ; it is exothermic .
(c) The forward reaction is endothermic ; it absorbs/takes in heat from the surroundings
.
This is quite a short question but worth paying attention to. It is asking you about
reversible reactions as well as energy transfer during reactions. Stay alert to
follow where the question takes you!
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Answer 13
(a) Sulfuric acid 
Give the name, not the formula. You can incorrectly spell a chemical name and
possibly still get the mark, but if you make just one small slip with a formula you
will not score at all.
(b) To ensure all the acid had reacted. 
(c) Filter it. 
(d) Crystallisation 
Not evaporation. You have to evaporate the solution for a time and stop before
any crystals are formed.
(e) Neutralisation 
(f) The pH would increase. 
You must answer the question. It is not the same to say that it would become
less acidic. The examiner wants to know that you understand the pH scale.
(g) By precipitating  a compound formed from lead ions/lead hydroxide .
(h) Pb2+(aq) + Ca(OH)2(aq) → Pb(OH)2(s) + Ca2+(aq) 
The 4 marks will be allocated as follows:

2 for the correct formulae (1 mark per side)

1 for correctly balancing the equation

1 for using correct state symbols
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Answer 14
(a) 2Cl– → Cl2 + 2e– 
1 mark is for Cl–, and 1 for balancing.
(b) The hydroxide (OH–) ion  makes the solution alkaline.
(c) Sodium hydroxide/NaOH is formed in solution in the cell. 
(d) Reduction 
If you use OIL RIG to help remember the difference between oxidation and
reduction, you must always include the electrons: thus, oxidation is loss of
electrons. If you omit these you could be implying the loss of any other species,
for example hydrogen.
(e) Al3+(l) + 3e– → Al(l) 
1 mark is for balancing and the other is for the liquid state symbol. The
electrolysis is done in the liquid state; aluminium oxide is insoluble in water.
(f) Oxygen is formed at the anodes  and reacts with the carbon  (to form carbon
dioxide).
(g) Aluminium oxide is dissolved in cryolite to reduce the melting point  and thus
reduce energy/electricity consumption .
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Answer 15
(a) The noble gases are missing. 
(b) 1 He left gaps for undiscovered elements. 
2 He moved some elements out of strict atomic mass order  (e.g. Te and I, and Ar
and K).
(c) Any three of the following:

Elements are arranged in order of proton (or atomic) number.

The number of protons is the atomic number.

The atomic number is the number of electrons.

The number of protons increases across a period.

Elements in the same group have same number of outer electrons. 
It is important to remember that it is the protons that determine the position of an
element in the periodic table, not the electrons.
(d) The difference between one atom and the next is a whole proton — parts of protons
cannot exist in an atom. 
(e)

The outer electron, which is lost in a reaction…

…is furthest from the rubidium nucleus.

This rubidium electron is more weakly attracted to the nucleus than the outer
sodium electron.

There is also more screening by inner electrons in rubidium…

…so the outer electron (of rubidium) is lost more easily. 
Any four of the above will score, as long as you have made the comparison
between the two atoms and correctly referred to the outer shell (energy level).
Not indicating the outer shell loses a mark.
(f) They all have same number (7) of electrons  in the outer shell .
It is best to be sure of the mark here and state the number of electrons in the
outer shell, as well as saying that they are the same in each element.
(g) There is less shielding in fluorine than in iodine (as fluorine has fewer shells than
iodine).  Fluorine therefore gains electrons more easily (because they are more
attracted to the nucleus). 
Comparison is again again needed here.
(h) The outer shell is full  so there is no tendency to lose or gain electrons .
2 marks are available here, so make sure two valid points are made.
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Answer 16
(a) Water that does not readily form a lather ; it reacts with soap to form scum .
(b) Calcium  Ca2+ ; Magnesium  Mg2+ 
(c) Either of the following will gain the mark:

Good for development/maintenance of teeth/bones.

It helps reduce heart disease. 
Saying ‘it is healthier’ will not score.
(d) There is a build-up of scale/calcium carbonate (CaCO3) is formed.  This means that
energy is wasted/it takes longer to boil/the kettle is less efficient. 
Remember that kettle fur is not scum. Scum is the precipitate formed when soap
reacts with hard water.
(e) The calcium ions/Ca2+/ magnesium ions/Mg2+  are replaced by hydrogen
ions/H+/sodium ions/Na+. 
There is no need to introduce you answer with something like ‘As the hard water
passes through the column…’.
(f) Sodium carbonate reacts  with the calcium/magnesium ions to form precipitates  of
calcium carbonate/magnesium carbonate.
Na2CO3(aq) + Ca2+(aq) → CaCO3(s) + 2Na+(aq) 
There is 1 mark for each side of the equation. Since this is a precipitation
reaction the state symbols are essential.
(g) Filtration removes solids.  Chlorination sterilises the water. 
(h) Carbon , silver  and ion exchange resins .
(i) It uses a lot of energy. 
There is no need to go into further detail.
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Answer 17
(a) Because the products are at a lower energy level than the reactants.  This shows that
heat is being released to the surroundings. 
(b) CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) 
1 mark is for correct formulae, 1 for balancing and 1 for correct state symbols. As
with all formulae and equations, just make sure that you write very clearly so that
the symbols are unambiguous, they cannot be mistaken for another element and
the numbers are subscript where necessary.
(c) Breaking the bonds in the reactants/methane and oxygen is endothermic/takes
in/absorbs energy. 
Making the bonds in the products/carbon dioxide and water is exothermic/releases
energy. 
More energy is released than is absorbed. 
You must not say that energy is made, produced or lost.
(d) It provides a different reaction pathway  that has a lower activation energy .
(e)
Take care that you make the curved line high enough above the product level,
so that the activation energy is clearly more than the difference between the
reactants and products. You will need to draw a horizontal line across from the
peak of the curve to make sure you show exactly what you mean by the
activation energy.
(f)
Breaking bonds
Bonds
Energy in kJ
3 × H–H
3 × 436
+1308 
1 × N≡N
1 × 944
+944 
Total
+2252
Making bonds
Bonds
Energy in kJ
6 × H–N
6 × 388
–2328
Total

–2328
Overall energy change = 2252 – 2328 = –76 kJ  Exothermic 
This type of calculation is best tackled using a table. It makes your calculations
easy to do and clear for the examiner to follow. It also reduces the chances of
you introducing errors and therefore increases the likelihood of your scoring full
marks.
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Answer 18
(a) Potassium ions: flame test ; lilac flame 
(b) Aluminium ions: add sodium hydroxide solution ; white precipitate forms  that
dissolves in excess hydroxide 
(c) Carbonate ions: add hydrochloric acid , effervescence/bubbles of gas produced 
There is no limewater available so you are not expected to describe the test for
carbon dioxide.
(d) Chloride ions: add silver nitrate solution acidified with dilute nitric acid ; white
precipitate forms 
(e) Sulfate ions: add barium chloride solution acidified with dilute hydrochloric acid ;
white precipitate forms 
(f) Aluminium ions do not produce a coloured flame. 
(g) Any four from the following points:

The hydrochloric acid is measured using a pipette.

The sodium hydroxide is used in a burette.

Note the initial reading on the burette.

Note the final reading on the burette/volume used.

Use of indicator described. 
You can use a labelled diagram to show the apparatus, but a few words of
description are probably easier and clearer.
(h) NaOH + HCl  NaCl  + H2O 
(i)
amount of sodium hydroxide 
24  0.4
1000
= 0.0096 mol 
1 mole of sodium hydroxide reacts completely with 1 mole of hydrochloric acid, so:
0.0096  1000
concentration of hydrochloric acid 
25.0
= 0.38(4) mol/dm3 
Make sure you clearly show the examiner what you are doing as the calculation
proceeds.
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Answer 19
(a) Nitrogen is taken from the air. 
(b) There is more chance of them colliding/coming into contact with each other. 
(c) The rate of reaction is increased by using an iron  catalyst , at high temperatures 
and high pressures .
(d) Percentage yield = 49% 
(e) Temperature: lower temperature increases yield  because equilibrium is moved to
the right , but rate of reaction is reduced .
Pressure: higher pressure increases yield  because equilibrium is moved to the
right .
Your answers here must be about yield not rate (but you are expected to note
that the lower temperature produces a greater yield at a slower rate).
(f) The reaction is too slow at low temperatures. 
The cost of manufacturing the equipment to withstand very high pressures is too
great/very high pressure increases the risk to safety. 
The idea of a compromise between yield and rate/cost will score 1 mark. Full
marks require a more specific answer relating to both temperature and pressure.
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Answer 20
(a) CnH2n+1OH 
(b) C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(l) 
1 mark is for correct formulae, 1 for balancing and 1 for correct state symbols.
(c) Ethanol burns with a clean flame/no soot , is a liquid, so easily
transported/contained  and releases a lot of energy .
(d) A weak acid does not ionise completely  in aqueous solution .
This is simply the definition; nothing more is needed.
(e) The pH of a weak acid is higher than the pH of a strong acid/is about 3 or 4 for a
weak acid, 0 or 1 for a strong acid. 
It is best to leave this as a comparison without trying to remember any specific
numbers, but ensure that it is a comparison, not just ‘weak acids have a higher
pH’.
(f) Ethyl ethanoate 
(g) Volatile means it vaporises easily. 
This is quite a straightforward topic to learn and prepare for the exam. The only
equations you can be quizzed on are the combustion of alcohols, so make sure
you know how to write them correctly and clearly.
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