Multiple Choice Questions (MCQ) topic quiz
Elements from the sea
Instructions and answers for teachers
These instructions cover the learner activity section which can be found on page 10. This
Lesson Element supports OCR AS and A Level Chemistry B (Salters).
When distributing the activity section to the learners either as a printed copy or as a
Word file you will need to remove the teacher instructions section.
The Activity
This Lesson Element is a teaching and learning resource containing 10 multiple choice
questions (MCQs) on the theme of elements from the sea. Some questions might require
synoptic thinking, using knowledge and ideas from various topics across the full A Level
content.
This resource can be used to test and consolidate understanding at the end of a topic or to
revisit and refresh knowledge at a later point in the course.
Learning Outcomes
This lesson element relates to the specification learning outcomes ES(a), ES(c), ES(d),
ES(e), ES(f), ES(h), ES(i), ES(j), ES(l), ES(m), ES(o), ES(p), ES(q).
Introduction
Multiple choice questions allow rapid coverage of a wide range of sub-topics.
Contrary to a widespread belief among students, multiple choice questions are not
necessarily easy – they can be easy, moderate or difficult.
The questions are written so that the incorrect answers are plausible distractors based on
common errors or misconceptions.
The questions in this quiz cover topics mainly from specification sections:
Elements from the sea.
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Multiple Choice Questions (MCQ) topic quiz - answers
1.
Which equation correctly shows the first ionisation enthalpy of bromine?
A
Br2(aq) + 2e–  2Br–(aq)
This is the half-equation for the reduction of
aqueous bromine, such as in a displacement
reaction.
B
Br(g) + e–  Br–(g)
This is the first electron affinity of bromine;
the learner may have been confused
because bromine normally forms a negative
ion.
C
Br(g)  Br+(g) + e–
Correct answer: The equation shows an
electron being lost from a gaseous atom.
D
Br(l)  Br+(g) + e–
The learner has used the standard state of
bromine instead of the gas state.
Your answer
2.
Which of these properties decreases down Group 17?
A
The atomic radius of the halogen
atoms.
The learner is confused about the direction of
the trend down the group.
B
The oxidising power of the
halogen elements.
Correct answer: As the halogen atoms get
larger they become less able to accept
electrons and act as oxidising agents.
C
The reducing power of the halide
ions.
As the size of the halide ions increases, they
become more likely to lose electrons and act
as reducing agents; the learner has confused
the oxidising power of halogens with the
reducing power of the halides.
D
The boiling point of the elements.
This mistake suggests quite a basic error; the
learner has either misread the question or is
not clear on the link between physical state
and boiling point.
Your answer
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C
2
B
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3.
What is the oxidation number of sulfur in Na2S4O6?
A
–1
The learner has calculated the oxidation state
of oxygen as being –1; seeing something
unusual about the molecule they are maybe
assuming that it is a peroxy compound.
B
+1.5
The learner has not taken into account the
charge on the sodium ions.
C
+2.5
Correct answer: If sodium and oxygen have
fixed oxidation states of +1 and –2
respectively, the four sulfur atoms add up to
+10 in total.
D
+6
Rushing the question – using a familiar
oxidation state of sulfur.
Your answer
4.
C
Aqueous solutions of four salts are electrolysed.
For the solution of which salt would you expect to observe a gas formed at the
cathode?
A
copper(II) chloride
Confusion between the anode and cathode –
chlorine gas is formed at the anode.
B
copper(II) iodide
The rules of aqueous electrolysis are not well
understood here as neither electrode would
have a gaseous product.
C
potassium nitrate
Correct answer: Hydrogen gas is formed at
the cathode as hydrogen ions will be more
readily reduced than potassium ions.
D
silver nitrate
Again the learner is considering the product
at the anode, which is oxygen in this case.
Your answer
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C
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5.
Fermentation is used to make ethanol. The equation for the reaction is given below,
along with the Mr values for each molecule.
C6H12O6(aq)  2C2H6O(aq) + 2CO2(g)
Mr values:
180
46
44
Which expression represents the atom economy for the reaction?
A
2  46  2  44 × 100%
The learner has included both products in the
calculation, rather than just the desired
product.
180
B
2  46  × 100%
Correct answer: There are two moles of
ethanol produced and carbon dioxide is a byproduct of the reaction.
180
C
D
46
× 100%
180
The learner has not taken into account that
two moles of ethanol are produced.
2  44  × 100%
The learner has used the Mr for carbon
dioxide instead of ethanol.
180
Your answer
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B
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6.
Which change would move the position of the following equilibrium towards the right?
I2(aq) + 2OH–(aq)
I–(aq) + IO–(aq) + H2O(l)
A
Adding solid potassium hydroxide
and stirring to dissolve it.
Correct answer: This would increase the
concentration of hydroxide ions, driving the
equilibrium position towards the right.
B
Adding solid potassium iodide
and stirring to dissolve it.
This would increase the concentration of
iodide ions, driving the equilibrium towards
the left – the learner may have misread the
question.
C
Adding sulfuric acid.
The learner is confused about the action of
acids and bases – adding acid would remove
hydroxide ions and lower their concentration,
moving the equilibrium towards the left hand
side.
D
Increasing the pressure.
The learner is perhaps confusing aqueous
reactants with gaseous, as there are more
moles of aqueous species on the left hand
side.
Your answer
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A
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7.
Which change in conditions would result in an increase in the concentration of HClO
produced in the following reaction?
Cl2(aq) + H2O(l)
HCl(aq) + HClO(aq)
H = negative
A
Decreasing the temperature.
Correct answer: Decreasing the
temperature will drive the equilibrium in the
exothermic (forward) direction, resulting in an
increase in products.
B
Increasing the temperature.
The learner is aware that temperature affects
the equilibrium position but has either
misread the question or ignored the
information about H.
C
Adding hydrochloric acid.
Addition of hydrochloric acid would drive the
equilibrium in the reverse direction.
D
Using a catalyst.
Catalysts increase the rate of both forward
and reverse reactions and have no effect on
the position of equilibrium.
Your answer
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A
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8.
When nitrogen dioxide is produced in a sealed syringe and allowed to stand, it
eventually forms an equilibrium mixture with dinitrogen tetroxide:
2NO2(g)
N2O4(g)
brown gas colourless gas
As the mixture moves towards equilibrium, which statement is true?
A
The N2O4 molecules don’t
decompose into NO2.
The learner has a static view of equilibrium,
where the reaction stops when the
concentration ratio reaches a certain point.
B
The volume of the gas mixture
increases.
The reaction mixture is starting from the
nitrogen dioxide side, meaning that as more
dinitrogen tetroxide is produced the volume
will decrease.
C
Correct answer: The mixture started with
The forward reaction rate
exceeds the reverse reaction rate. only reactants so at the start the reverse
reaction rate will be zero. Hence, the forward
rate will always be greater than the reverse
until the point at which the rates are equal.
D
The brown colour gets darker.
The learner is confused about the information
given – the reaction mixture will lighten as
more nitrogen dioxide is converted.
Your answer
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C
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9.
The concentration of iodine present in a mixture can be determined by titration with
sodium thiosulfate, according to the following equation:
I2 + 2Na2S2O3  2NaI + Na2S4O6
Which statement is true for this titration?
A
The iodine acts as a reducing
agent.
The learner is perhaps thinking about the
action of iodide ions, which are often seen in
the context of reducing agents.
B
The mixture turns from colourless
to brown.
The learner is confused about the colours of
iodine and iodide.
C
The ratio between oxygen and
sulfur stays the same, so the
oxidation state of the sulfur
doesn’t change.
The learner has not taken into account the
charge on the sulfur-containing ions when
determining the oxidation state of the sulfur.
D
The titration can be used to
indirectly determine the
concentration of chlorine in
swimming pool water.
Correct answer: The learner could arrive at
this answer via a process of elimination;
however, it is also a logical step that the
iodine titrated could have been liberated by a
displacement of iodide ions by aqueous
chlorine.
Your answer
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D
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10.
Which of the following statements is/are true of the sulfur compounds formed when
solid potassium bromide is reacted with concentrated sulfuric acid?
1.
Potassium hydrogen sulfate is formed.
2.
Sulfur dioxide is formed.
3.
Hydrogen sulfide is formed.
A
1,2 and 3
The learner is confusing the reaction of
bromide salts with that of iodide salts, which
are stronger reducing agents.
B
only 1 and 2
Correct answer: The bromide ion is a strong
enough reducing agent to reduce sulfur to a
+4 oxidation state in sulfur dioxide, but not to
produce its –2 oxidation state in hydrogen
sulfide.
C
only 2 and 3
A common mistake; the learner is taking an
‘either or’ approach to the reaction (the halide
can either accept a proton or behave as a
reducing agent).
D
only 1
The learner is confusing the reactions of
bromide salts with the reactions of chloride or
fluoride salts, and has not taken into account
the reducing ability of the bromide ion.
B
Your answer
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Multiple Choice Questions (MCQ) topic quiz
Elements from the sea
Learner Activity
1.
Which equation correctly shows the first ionisation enthalpy of bromine?
A
Br2(aq) + 2e–  2Br–(aq)
B
Br(g) + e–  Br–(g)
C
Br(g)  Br+(g) + e–
D
Br(l)  Br+(g) + e–
Your answer
2.
Which of these properties decreases down Group 17?
A
The atomic radius of the halogen atoms.
B
The oxidising power of the halogen elements.
C
The reducing power of the halide ions.
D
The boiling point of the elements.
Your answer
3.
What is the oxidation number of sulfur in Na2S4O6?
A
–1
B
+1.5
C
+2.5
D
+6
Your answer
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© OCR 2016
4.
Aqueous solutions of four salts are electrolysed.
For the solution of which salt would you expect to observe a gas formed at the
cathode?
A
copper(II) chloride
B
copper(II) iodide
C
potassium nitrate
D
silver nitrate
Your answer
5.
Fermentation is used to make ethanol. The equation for the reaction is given below,
along with the Mr values for each molecule.
C6H12O6(aq)  2C2H6O(aq) + 2CO2(g)
Mr values:
180
46
44
Which expression represents the atom economy for the reaction?
A
2  46  2  44 × 100%
180
B
2  46  × 100%
180
C
D
46
× 100%
180
2  44  × 100%
180
Your answer
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© OCR 2016
6.
Which change would move the position of the following equilibrium towards the right?
I2(aq) + 2OH–(aq)
I–(aq) + IO–(aq) + H2O(l)
A
Adding solid potassium hydroxide and stirring to dissolve it.
B
Adding solid potassium iodide and stirring to dissolve it.
C
Adding sulfuric acid.
D
Increasing the pressure.
Your answer
7.
Which change in conditions would result in an increase in the concentration of HClO
produced in the following reaction?
Cl2(aq) + H2O(l)
HCl(aq) + HClO(aq)
A
Decreasing the temperature.
B
Increasing the temperature.
C
Adding hydrochloric acid.
D
Using a catalyst.
H = negative
Your answer
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8.
When nitrogen dioxide is produced in a sealed syringe and allowed to stand, it
eventually forms an equilibrium mixture with dinitrogen tetroxide:
2NO2(g)
N2O4(g)
brown gas colourless gas
As the mixture moves towards equilibrium, which statement is true?
A
The N2O4 molecules don’t decompose into NO2.
B
The volume of the gas mixture increases.
C
The forward reaction rate exceeds the reverse reaction rate.
D
The brown colour gets darker.
Your answer
9.
The concentration of iodine present in a mixture can be determined by titration with
sodium thiosulfate, according to the following equation:
I2 + 2Na2S2O3  2NaI + Na2S4O6
Which statement is true for this titration?
A
The iodine acts as a reducing agent.
B
The mixture turns from colourless to brown.
C
The ratio between oxygen and sulfur stays the same, so the oxidation state of the
sulfur doesn’t change.
D
The titration can be used to indirectly determine the concentration of chlorine in
swimming pool water.
Your answer
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10.
Which of the following statements is/are true of the sulfur compounds formed when
solid potassium bromide is reacted with concentrated sulfuric acid?
1.
Potassium hydrogen sulfate is formed.
2.
Sulfur dioxide is formed.
3.
Hydrogen sulfide is formed.
A
1,2 and 3
B
only 1 and 2
C
only 2 and 3
D
only 1
Your answer
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