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Sample Questions

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Questions
Q7.
This question is about the reaction between sodium carbonate solution and dilute nitric acid.
Na2CO3(aq) + 2HNO3(aq) → 2NaNO3(aq) + CO2(g) + H2O(l)
(a) What is the ionic equation for this reaction?
(1)
A
Na2CO3(aq)
+
B
Na+(aq)
+
2H+(aq)
→
→
C
+
2H+(aq)
→
D
+
2HNO3(aq)
→
2Na+(aq)
+
CO2(g)
+
H2O(l)
NaNO3(aq)
CO2(g) +
H2O(l)
+
CO2(g) + H2O(l)
(b) What is the volume of carbon dioxide produced from the complete reaction of 0.10 mol of nitric acid
at room temperature and pressure?
[1 mol of any gas occupies 24 dm3 at room temperature and pressure.]
(1)
A
1.2 dm3
B
1.8 dm3
C
2.4 dm3
D
3.6 dm3
(c) What volume of sodium carbonate solution of concentration 0.500 mol dm−3, would be needed to
completely react with 25.0 cm3 of nitric acid of concentration 0.250 mol dm−3?
(1)
A
6.25 cm3
B
12.50 cm3
C
18.75 cm3
D
25.00 cm3
Q8.
This question is about magnesium.
The relative atomic mass of a sample of magnesium was found to be 24.3. The percentage composition
for two of the three isotopes is given in the table. Use these data to calculate the percentage composition
of the third isotope and hence its relative isotopic mass. Give your answer to an appropriate number of
significant figures. You must show your working.
(4)
(Total for question = 4 marks)
Q9.
The labels on four colourless solutions had fallen off in storage. It was known that the solutions were:
In order to identify each solution, a number of tests were carried out.
(a) Solutions can be sprayed into a flame to produce a flame colour identical to that seen in the more
conventional method with a solid on a nichrome wire.
Which solution would produce a lilac flame?
(1)
A
hydrochloric acid
B
C
D
magnesium sulfate
potassium chloride
sodium carbonate
(b) Which of the following diagrams best illustrates the electronic transitions that take place during a
flame test?
(1)
(c) Which solution produces a white precipitate with acidified barium chloride solution?
(1)
A
B
C
D
hydrochloric acid
magnesium sulfate
potassium chloride
sodium carbonate
(d) Two of the solutions produce the same result on the addition of dilute nitric acid followed by silver
nitrate solution.
State the observation with this test and the two solutions that give this result.
(2)
Observation
.............................................................................................................................................
Solutions
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(e) The hydrochloric acid and the sodium carbonate solution react together. State an observation you
would make and write the ionic equation for the reaction. State symbols are not required.
(2)
Observation
.............................................................................................................................................
Ionic equation
(Total for question = 7 marks)
Q10.
This question is about chlorine and its compounds.
When chlorine gas is dissolved in water, it reacts according to the equation
The chloric(I) acid (HClO) produced is much more effective as a disinfectant than
dissolved chlorine.
Chloric(I) acid is a weak acid and has little effect on the pH of the water.
Swimming pools usually have a chlorine content of 1 – 3 ppm.
Use the equation to explain one disadvantage of a chlorine content that is
much lower than 1 ppm and one disadvantage of a chlorine content that is much
higher than 3 ppm.
(4)
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(Total for question = 4 marks)
Q11.
(c)
A partially balanced equation for the complete combustion of butane is:
C4H10 + xO2 → 4CO2 + 5H2O
The number of moles of oxygen, x, needed to balance this equation is
(1)
A
B
C
D
(d)
4.5
6.5
9
13
Incomplete combustion of butane produces a mixture of products.
Which substance is not produced during the incomplete combustion of butane?
(1)
A
B
C
D
C
CO
H2
H2O
Q12.
The table shows some information about a selection of elements and compounds.
The compressive strength is a measure of the energy required to break
some of the bonds within a substance.
Deduce possible reasons why there are two widely different values for the compressive
strength of graphite.
Both the values (2.3 and 15.3 GPa) are valid experimental results.
(2)
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(Total for question = 2 marks)
Q13.
Which are the correct names for both SO2 and Na2SO4?
(1)
A
sulfur oxide(II) and sodium sulfate(IV)
B
sulfur(II) oxide and sodium(II) sulfate
C
sulfur oxide(IV) and sodium sulfate(IV)
D
sulfur(IV) oxide and sodium sulfate(VI)
Q14.
This question is about covalent bonds.
State what is meant by the term covalent bond.
(2)
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(Total for question = 2 marks)
Q15.
Some metal carbonates also undergo thermal decomposition.
(i) Draw a diagram of the apparatus that could be used to compare the ease of thermal decomposition
of lithium carbonate, Li2CO3, and magnesium carbonate, MgCO3.
(2)
(ii) State one way in which you would ensure a fair test.
(1)
.............................................................................................................................................
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(iii) State how data obtained in this experiment could be used to make a comparison.
(1)
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(Total for question = 4 marks)
Q16.
The table shows some information about a selection of elements and compounds.
Deduce two possible reasons why the density of iron (7.86 g cm−3) is much greater
than the density of graphite (2.2 to 2.8 g cm−3).
(2)
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(Total for question = 2 marks)
Q17.
This question is about covalent bonds.
Draw a diagram of the ammonia molecule, clearly showing its shape.
Include any lone pairs of electrons and the value of the bond angle.
(2)
(Total for question = 2 marks)
Examiner's Report
Q1.
This proved to be a high-scoring question, with a mean of over 1.7. It was pleasing that candidates were
able to identify and to correct a number of errors in the excerpt which demonstrates a good level of
understanding of this topic area. The most common correct response, not unsurprisingly, was the
statement that electrons are found in the nucleus. Occasionally an incorrect comment to the effect that
the isotopes had 18 or 20 electrons in the shells was seen.
Results Plus: Examiner Comments
An example of a good response which scores both marks.
Results Plus: Examiner Tip
It can often be a helpful practice when constructing an answer for key parts in the
question to be highlighted or 'ringed' as in this instance.
Q2.
No Examiner's Report available for this question
Q3.
Over a third of candidates could correctly calculate the atom economy and these proved to be
the more able candidates. Occasionally the mark was lost despite correct working because of
incorrect rounding.
Results Plus: Examiner Comments
An example of the error that some candidates made is thinking that atom economy is
determined by dividing the number of moles.
Results Plus: Examiner Tip
Learn the correct expression for atom economy and its significance.
Q4.
No Examiner's Report available for this question
Q5.
No Examiner's Report available for this question
Q6.
Even those at the grade A boundary had a mean of 0.96 and so this proved to be a challenging
question for all. Occasionally correct comments about radii were negated by reference to ions.
Candidates have a heightened need for care in their choice of words and terms used in this type
of question.
Results Plus: Examiner Comments
In this response the common error of attributing the bond length to differences in
electronegativity is seen. The score for this response was zero.
Results Plus: Examiner Comments
It is evident from the answer shown here that the candidate has a good level of
understanding and due to the reference to the increased shielding and atomic radius of
sulphur the S-H bond length increases in comparison to the O-H bond length. This
scored two marks. Unfortunately the effect of this, namely that there will subsequently
be less attraction for the bonding electron pair, is missing.
Q7.
No Examiner's Report available for this question
Q8.
This calculation was extremely well done in general. Many were able to score full marks, laying
out their work in an easily understandable way. Some assumed the isotopic mass of the missing
isotope was 24 and calculated the relative atomic mass, which limited their marks as this was not
what they were asked to do.
Results Plus: Examiner Comments
This clearly laid out example was a good answer scoring full marks.
Results Plus: Examiner Tip
Clearly laid out answers are both easier to read and mark but they also help to organise
and direct your thoughts during a calculation when the route to the end may not always
be obvious.
Some candidates decided to assume that the value was 24 and then calculate the value of the
relative atomic mass. This was not what they were asked to do, however.
Results Plus: Examiner Comments
This example of the approach outlined scores 1 mark for the percentage of the third
isotope.
Q9.
(d)
A useful discriminatory question with the grade A candidates scoring both marks but only the
better of the less able candidates able to score one mark. The observation mark required both
the colour and state. The mark for the identity of the solutions proved the more challenging and
both solutions had to be correct for the one mark to be awarded.
Results Plus: Examiner Comments
The observation is correct. The identity of the solutions are also correct as either names
or formulae, or both as seen here, were acceptable.
Results Plus: Examiner Tip
If the name or formula is not explicitly asked in the question then either will be
acceptable. However, if both the name and formula are given for one substance then
both must be correct otherwise it will be a case of the incorrect response negating the
correct one.
(e)
Part (e) proved to be much harder for candidates to get right than part (d) with even the
candidates at the grade A boundary scoring a mean of about 1.5 out of 2.
The ionic equation, as usual, was a key discriminator with only the more able candidates able to
select the correct species and to produce a balanced equation.
Results Plus: Examiner Comments
The observation mark was awarded for the reference to "it fizzes". Nothing else was
creditworthy.
Results Plus: Examiner Tip
Carbon dioxide, oxygen or hydrogen gas are not observed and so the comment that
"CO2 given off" does not gain any credit. A suitable observation is bubbles, fizzing or
effervescence.
Results Plus: Examiner Comments
The spelling "effervesons" is incorrect but unambiguous and so the mark for the
observation was awarded.
Unfortunately this candidate has not checked the balancing of the equation by charge
and so the second mark was not given.
Q10.
Many candidates did not use the equation to reach their conclusions, restricting their answers
simply to the effects of more/less chlorine in solution. These answers were not awarded any
marks. Zero marks were quite common for this question.
MP1/MP2 required recognition of the variation in HClO (concentration), and its effect on
disinfection of the water.
MP3/MP4 required recognition of the variation in HCl (concentration), and its effect on the acidity
of the pool.
Q11.
No Examiner's Report available for this question
Q12.
This question presented candidates with unusual information and asked them to relate this to the
structure of graphite. The response was disappointing. Some candidates seemed aware of the
presence of weak and strong bonds, but failed to relate this to the structure, let alone name the
types of bonding present. Considerable flexibility was allowed (particularly for MP1) in describing
the type of bonds present.
Q13.
No Examiner's Report available for this question
Q14.
On this question, a number of students were able to respond with answers which mentioned
sharing a pair of electrons, an idea which is common at GCSE level, but must be developed
further for AS. To score, students need to recognise that the bond was an attraction between the
nucleii of the two atoms bonded together and the shared pair of electrons.
This example clearly shows the refinement of the GCSE ideas required at AS level.
Results Plus: Examiner Comments
Clearly stating that the bond is the electrostatic attraction between nucleii and a shared
pair of electrons, this example scored 2.
This question extends an idea encountered at GCSE where the bond between non-metal atoms
involves the sharing of electrons.
Results Plus: Examiner Comments
At AS, ideas first encountered at GCSE are refined and improved. This student has
remembered the basic idea, but has not included any of the refinement of knowledge
which is required here. To score two marks, this student needed to mention the nucleii
and the attraction between these and the shared pair of electrons, so this scores 0.
Results Plus: Examiner Tip
A glossary of definitions is a valuable resource for revision. Careful consideration of
definitions is important to ensure the key elements are present. A covalent bond
requires an attraction between two nucleii and a shared pair of electrons.
Q15.
The diagrams seen of the experimental apparatus in this question certainly left a lot to be desired.
They did raise the question whether the candidates had actually done any practice in drawing
such apparatus and indeed whether they had done or seen a similar practical. However, it is
noted that while there is no core practical of this activity, the specification does state that student
should understand "experimental procedures to show". The removal of coursework assessment
and the emphasis on practical in examinations should encourage centres and their candidates to
practice such activities.
An example of the total lack of appreciation of the task required was when a heated crucible was
drawn with no attempt, practical or otherwise, at collecting any gas that could be evolved. In
addition, a number of candidates 'lost track' of where they were in the question or went into
'autopilot' by adding hydrochloric acid to the carbonate rather than heating it.
In part (ii) few correctly referred to the Bunsen setting or distance from the test-tube, with the
most common error being the use of the 'same mass' which although would still work to show the
difference it does not answer the question of how to ensure a fair test.
The question in part (iii) asked for data that could be used to make a comparison and a number
of less able responses simply stated "the time it takes for the carbonate to decompose" which
fails to either give a comparison or how the decomposition would be evident.
Results Plus: Examiner Comments
The diagram in this response is an illustration of one of the errors mentioned above,
namely that the tube with the limewater is sealed and so there is no way for the gas to
escape. The bung/cork in the top of the test-tube with the carbonate would clearly allow
the gas to escape and so scored one mark for part (i).
This response also has the common error of "same mass" of carbonate in part (ii) which
did not score, however the mark was awarded for part (iii).
Results Plus: Examiner Tip
Practice drawing experimental or practical apparatus and make sure that it will achieve
its purpose.
Results Plus: Examiner Comments
The diagram in part (i) also illustrates another common error in that there appears to be
a solid bung/cork in the test-tube with the carbonate and so there is no way for the gas
to escape. In addition, the delivery tube seems to be going into a sealed test-tube,
although the drawing is rather unclear.
Both parts (ii) and (iii) scored the marks for suitable answers.
Q16.
The majority of candidates scored just one of the available two marks.
MP2 was awarded quite frequently, with most candidates discussing the close packing in iron
rather than the idea of space (between the atoms/layers) in graphite.
MP1 was awarded relatively infrequently, perhaps because the previous question related to
structure, so few candidates thought about the mass of the individual particles.
Q17.
Drawing three dimensional diagrams to show the shape of molecules is an important chemical
skill. Three dimensional shapes involve the use of 'dot' or 'hash' bonds and 'wedge' bonds.
These show the direction of bonds going behind or in front of the plane of the paper respectively.
A normal line shows a bond in the plane of the paper. Many students scored marks for good
diagrams, but some simply did dot-and-cross bonding diagrams or diagrams using just lines
which limited their ability to score marks.
Drawing 3 dimensional diagrams is an important skill needed to show the shape of molecules. A
number of standard bond angles needs to be learnt and applied to both familiar and unfamiliar
molecules.
Results Plus: Examiner Comments
This student has been taught to use a wedge to show an atom coming out of the plane
of the paper toward the reader, and a hatched wedge that suggests the bond is going
into the paper away from the reader. This is an excellent diagram and scored 1 mark.
The bond angle of 107° which was correct has unfortunately been replaced by the
incorrect angle of 104.5° so this scores 1 mark.
Results Plus: Examiner Tip
Learn the standard bond angles and practice applying them to unfamiliar molecules.
Results Plus: Examiner Comments
This example has the correct bond angle labelled, but there has been no attempt at a 3
dimensional diagram so this scores 1 mark.
Results Plus: Examiner Tip
Diagrams showing the shape of molecules involve three types of lines to represent the
bonds, straight lines, wedges and hatched lines. Drawing diagrams is a difficult skill
which comes with practice.
Mark Scheme
Q1.
Q2.
Q3.
Q4.
Q5.
Q6.
Q7.
Q8.
Q9.
Q10.
Q11.
Q12.
Q13.
Q14.
Q15.
Q16.
Q17.
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