Multiple Choice Questions (MCQ) topic quiz
Oceans
Instructions and answers for teachers
These instructions cover the student activity section which can be found on page 9. This
Lesson Element supports OCR A Level Chemistry B (Salters).
When distributing the activity section to the students 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 oceans. 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 O(b), O(d), O(e),
O(f), O(h), O(i), O(l), O(m), O(n).
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:
Oceans.
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Multiple Choice Questions (MCQ) topic quiz - answers
1.
Which statement about the greenhouse effect is true?
A
Absorption of infrared radiation
causes homolytic fission and
creates radicals.
Infrared energy is not of a high enough
frequency to cause electron excitation or
photolysis.
B
Oxygen molecules do not absorb
infrared radiation.
Correct answer: Oxygen does not have a
dipole moment and so does not absorb
infrared radiation.
C
Greenhouse gases reflect infrared Greenhouse gases do not reflect; the
radiation back to the Earth’s
molecules absorb infrared radiation and then
surface, trapping the heat.
re-emit it in all directions, resulting in some
going back towards the Earth’s surface.
D
Solar energy reaches the Earth
mainly as infrared radiation.
Most solar energy reaches the Earth’s
surface as UV and visible light.
Your answer
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B
© OCR 2016
2.
The boiling points of some hydrocarbons are listed below.
Name and formula of hydrocarbon
Propane, C3H8
Butane, C4H10
Pentane, C5H12
Hexane, C6H14
Boiling point / K
231
273
309
342
What is the correct order for the standard entropy for these hydrocarbons, from
lowest to highest?
A
butane, propane, hexane,
pentane
The learner has placed the molecules in
order of decreasing, rather than increasing
molar entropy.
B
hexane, pentane, butane,
propane
The learner has simply placed the molecules
in order of decreasing size.
C
pentane, hexane, propane,
butane
Correct answer: Liquids have lower molar
entropies than gases. If the molecule is in the
same state then the larger molecule has the
greater entropy as it has a greater number of
energy levels.
D
propane, butane, pentane,
hexane
The learner has assumed that molar entropy
increases with molecular size (true) but has
not taken into account their state at room
temperature.
Your answer
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C
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3.
surrS for a reaction is –16.5 J mol–1 K–1 at 298 K.
What is the value of the enthalpy change for this reaction?
A
–55.4 kJ mol–1
The learner has performed the same mistake
as in D but has also neglected to change the
sign of their answer.
B
–4.92 kJ mol–1
The learner has forgotten that the sign of surrS
is always opposite to the sign of H.
C
+4.92 kJ mol–1
Correct answer: Rearranging the equation
gives H = –surrS × T; the answer is then
divided by 1000 to give the answer in kJ mol–1.
D
+55.4 kJ mol–1
The learner has not correctly rearranged the
equation. They have divided –surrS by 298 and
multiplied by 1000 (as if surrS and H were
interchangeable).
Your answer
4.
Which species is the conjugate base of the acid HSO3–?
A
H2SO4
This is not related to the HSO3– ion at all, and
is simply a more familiar molecule.
B
H2SO42–
Here the learner has added OH– to the ion,
thinking of acid behaviour as a molecule that
reacts with hydroxide ions rather than
producing H+.
C
H2SO3
This is the conjugate acid of the ion.
D
SO32–
Correct answer: This is the species formed
when the ion acts as an acid (proton donor).
Your answer
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C
4
D
© OCR 2016
5.
Which statement is true of buffer solutions?
A
A buffer does not change in pH
when small amounts of acid or
alkali is added.
This is a common misconception – the pH will
always change, but only very slightly.
B
An acidic buffer is a mixture of a
weak acid and a solution of its
salt.
Correct answer: These are the core
components of an acidic buffer, providing a
‘reservoir’ of HA and A– to allow the
equilibrium position to shift in response to
changes in H+ concentration.
C
All buffers are acidic.
Buffers can also be alkaline if they are made
from a combination of a weak base and its
salt.
D
The pH of a buffer depends only
on the ratio of its components’
concentrations.
If this statement specified room temperature,
it would be true; however the pH of any buffer
solution also depends on temperature as this
will affect the value of Ka and thus the
equilibrium position.
Your answer
6.
What is the hydroxide ion concentration in a solution for which pH = 4?
A
1010 mol dm–3
Incorrect rearrangement of the Kw equation
([OH–] = [H+]/Kw).
B
10–4 mol dm–3
The learner has worked out the hydrogen ion
concentration.
C
10–10 mol dm–3
Correct answer: Correct rearrangement of
the Kw equation gives [OH–] = Kw/[H+].
D
10–18 mol dm–3
Incorrect rearrangement of the Kw equation
([OH–] = Kw × [H+]).
Your answer
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B
5
B
© OCR 2016
7.
Calcium phosphate is a sparingly soluble solid. The equation for the dissolving
process is shown below:
Ca3(PO4)2(aq)
3Ca2+(aq) + 2PO43–(aq)
What are the units for the solubility product, Ksp, for this process?
A
mol4 dm–12
The learner has multiplied the concentration
terms on the right but has divided them by a
concentration term from the left hand side for
the solid calcium phosphate.
B
mol5 dm–15
Correct answer: Ksp = [Ca2+]3[PO43–]2 so the
units are calculated by (mol dm–3)5.
C
mol5 dm–15 s–1
The learner is confusing equilibrium
constants with rate constants and so has
included a time component.
D
it has no units
The learner is perhaps confused about the
nature of heterogeneous equilibrium
constants and has taken the fact that the left
hand side is not included in the equation as
meaning the constant has no units.
Your answer
8.
Which of the following processes is associated with hydH?
A
XY(s)  X+(aq) + Y–(aq)
This is the solH. The two processes have
similar names and are thus often confused.
B
X+(s)  X+(aq)
The state symbols here are incorrect. The
learner has not taken into account the energy
required to break the ion away from the
lattice.
C
XY(s)  X+(g) + Y–(g)
This is the reverse of the lattice enthalpy.
D
X+(g)  X+(aq)
Correct answer: This is the energy released
upon hydration of a gaseous ion.
Your answer
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B
6
D
© OCR 2016
9.
An experiment was carried out to determine the standard enthalpy change of solution
for a compound which readily dissolves at room temperature. During the dissolving
process a decrease in temperature was recorded.
What can be assumed from these results?
A
The compound dissolves more
readily at lower temperatures.
The dissolving process is endothermic,
therefore surrS is negative. Since
surrS = –H/T, it follows that surrS will
become more negative at lower
temperatures, making totS more negative
and dissolving less likely to be spontaneous.
B
The dissolving process has a
positive surrS.
If the process is endothermic then surrS will
be negative.
C
The dissolving process has a
positive sysS.
Correct answer: If the compound readily
dissolves at room temperature then totS
must be positive. Since surrS is negative it
follows that sysS must be positive to
compensate.
D
The process has a high activation
energy.
Nothing can be ascertained about the
activation energy as this will only affect the
rate of dissolving. The learner is associating
an endothermic reaction with a high
activation energy.
Your answer
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C
© OCR 2016
10.
The pH of an acidic buffer solution can be calculated from rearrangement of the Ka
equation below:
Ka = [H+][A–]/[HA]
Which statement(s) is/are true for this calculation?
Statement 1: The exact concentrations of A– and HA do not need to be known, only
their molar ratio.
Statement 2: The pH will also be dependent on temperature.
Statement 3: It can be approximated that [H+] = [A–]
A
1, 2 and 3
Statement 3 is not true for a buffer solution,
only for a weak acid alone. In a buffer
solution a significant quantity of the anion is
added to the mixture.
B
only 1 and 2
Correct answer: The pH depends on the
ratio of salt/acid and the Ka; the Ka is also
dependent on temperature.
C
only 2 and 3
The learner does not appreciate that the units
for A– and HA cancel out in the equation and
so a simple molar ratio is sufficient to carry
out the calculation.
D
only 1
The learner has forgotten that Ka is only
constant at a given temperature.
Your answer
B
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Multiple Choice Questions (MCQ) topic quiz
Oceans
Learner Activity
1.
Which statement about the greenhouse effect is true?
A
Absorption of infrared radiation causes homolytic fission and creates radicals.
B
Oxygen molecules do not absorb infrared radiation.
C
Greenhouse gases reflect infrared radiation back to the Earth’s surface,
trapping the heat.
D
Solar energy reaches the Earth mainly as infrared radiation.
Your answer
2.
The boiling points of some hydrocarbons are listed below.
Name and formula of hydrocarbon
Propane, C3H8
Butane, C4H10
Pentane, C5H12
Hexane, C6H14
Boiling point / K
231
273
309
342
What is the correct order for the standard entropy for these hydrocarbons, from
lowest to highest?
A
butane, propane, hexane, pentane
B
hexane, pentane, butane, propane
C
pentane, hexane, propane, butane
D
propane, butane, pentane, hexane
Your answer
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© OCR 2016
3.
surrS for a reaction is –16.5 J mol–1 K–1 at 298 K.
What is the value of the enthalpy change for this reaction?
A
–55.4 kJ mol–1
B
–4.92 kJ mol–1
C
+4.92 kJ mol–1
D
+55.4 kJ mol–1
Your answer
4.
Which species is the conjugate base of the acid HSO3–?
A
H2SO4
B
H2SO42–
C
H2SO3
D
SO32–
Your answer
5.
Which statement is true of buffer solutions?
A
A buffer does not change in pH when small amounts of acid or alkali are
added.
B
An acidic buffer is a mixture of a weak acid and a solution of its salt.
C
All buffers are acidic.
D
The pH of a buffer depends only on the ratio of its components’ concentrations.
Your answer
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© OCR 2016
6.
What is the hydroxide ion concentration in a solution for which pH = 4?
A
1010 mol dm–3
B
10–4 mol dm–3
C
10–10 mol dm–3
D
10–18 mol dm–3
Your answer
7.
Calcium phosphate is a sparingly soluble solid. The equation for the dissolving
process is shown below:
Ca3(PO4)2(aq)
3Ca2+(aq) + 2PO43–(aq)
What are the units for the solubility product, Ksp, for this process?
A
mol4 dm–12
B
mol5 dm–15
C
mol5 dm–15 s–1
D
it has no units
Your answer
8.
Which of the following processes is associated with hydH?
A
XY(s)  X+(aq) + Y–(aq)
B
X+(s)  X+(aq)
C
XY(s)  X+(g) + Y–(g)
D
X+(g)  X+(aq)
Your answer
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© OCR 2016
9.
An experiment was carried out to determine the standard enthalpy change of solution
for a compound which readily dissolves at room temperature. During the dissolving
process a decrease in temperature was recorded.
What can be assumed from these results?
A
The compound dissolves more readily at lower temperatures.
B
The dissolving process has a positive surrS.
C
The dissolving process has a positive sysS.
D
The process has a high activation energy.
Your answer
10.
The pH of an acidic buffer solution can be calculated from rearrangement of the Ka
equation below:
Ka = [H+][A–]/[HA]
Which statement(s) is/are true for this calculation?
Statement 1: The exact concentrations of A– and HA do not need to be known, only
their molar ratio.
Statement 2: The pH will also be dependent on temperature.
Statement 3: It can be approximated that [H+] = [A–]
A
1, 2 and 3
B
only 1 and 2
C
only 2 and 3
D
only 1
Your answer
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© OCR 2016