Multiple choice practice test
The Ozone Story
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 contains 10 multiple choice questions on topics covered in the
teaching module The ozone story.
The question worksheet can be used to consolidate understanding at the end of teaching the
module, to revisit and refresh knowledge at a later point in the course, or during exam
preparation.
Learning Outcomes
This lesson element relates to the specification learning outcomes OZ(a), OZ(b), OZ(c),
OZ(f), OZ(g), OZ(k), OZ(l), OZ(m), OZ(n), OZ(q), OZ(r), OZ(t), OZ(u).
Introduction
Multiple choice questions form part of the written assessment in GCE Chemistry B (Salters)
at both AS and A Level. Besides a means of assessing knowledge of content, this question
worksheet therefore also provides useful preparation for the examinations.
The questions are written so that the incorrect answers are plausible distractors based on
common errors or misconceptions. In the Answers section below, guidance is given on the
reason for including each distractor. This information can be used as a basis for formative
feedback, or for the planning of remedial revision sessions.
These questions cover topics from the teaching module The ozone story.
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Multiple Choice practice test answers
1. Which molecule is polar?
A
BF3
BF3 is trigonal planar – the learner may
neglect to realise this if they do not draw the
dot and cross diagram, or if they assume the
presence of a lone pair.
B
CO2
CO2 is a classic example of a linear molecule
where the polarity of the carbon–oxygen
bonds is cancelled out by molecular
symmetry.
C
NH3
Correct answer: The pyramidal shape
means there is an overall dipole moment in
ammonia.
D
SO3
A trickier molecule to interpret in terms of dotand-cross diagrams, but the learner should
appreciate that sulfur forms three double
bonds and therefore the shape is
symmetrical.
Your answer
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C
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2.
What intermolecular forces are present between molecules of methanal, HCHO?
A
instantaneous dipole–induced
dipole bonds only
The learner may be assuming that the bond
polarities are cancelled out by symmetry,
however this is not the case.
B
hydrogen bonds and
instantaneous dipole–induced
dipole bonds
The learner is likely assuming the presence
of an –OH group; they also do not appreciate
that the presence of hydrogen bonding would
indicate the presence of all three
intermolecular bonds.
C
permanent dipole–permanent
dipole bonds only
The learner has correctly identified
permanent dipole–permanent dipole bonds
as being the strongest intermolecular bonds,
but has not appreciated that instantaneous
dipole–induced dipole bonds are also
present.
D
permanent dipole–permanent
dipole bonds and instantaneous
dipole–induced dipole bonds
Correct answer: The carbon–oxygen bond
creates a permanent dipole in addition to the
instantaneous dipole–induced dipole bonds.
Your answer
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D
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3.
Hydrofluoroalkanes, such as CH2F2, have been considered as an alternative to
CFCs.
Why are hydrofluoroalkanes preferable compounds?
A
They do not have as high a
greenhouse factor.
The learner is confusing the environmental
effects of exacerbated greenhouse effect and
ozone depletion.
B
They break down in the
troposphere and do not reach the
stratosphere, so do not damage
the ozone layer.
The carbon–fluorine bond is too strong to be
broken by UV radiation in the troposphere or
stratosphere; this explanation would apply to
hydrobromoalkanes.
C
The bonds are not broken by UV
radiation in the stratosphere, so
they do not cause ozone
depletion.
Correct answer: The strength of the carbon–
fluorine bond means that radicals do not form
in the stratosphere.
D
They are less flammable and less
toxic.
The original CFC compounds were utilised
specifically because of their low toxicity and
flammability.
Your answer
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C
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4.
The Maxwell–Boltzmann distribution of energy for gaseous particles under two
different sets of conditions, X and Y, is shown below.
Which statement can be deduced from the distribution?
A
Y is at a lower concentration than
X.
The learner has perhaps mistakenly
interpreted the lower maximum of the Y curve
as representing a smaller number of
particles.
B
X and Y are at different
pressures.
The learner is confused about the
mechanism by which pressure affects
reaction rate and is perhaps confusing
number of particles with the activation energy
with number of collisions.
C
Y is in the presence of a catalyst.
In the presence of a catalyst there would be
more particles with greater than or equal to
the activation energy, but this would be due
to the EA being lowered rather than more
particles being above this energy.
D
Y is at a higher temperature than
X.
Correct answer: The graph shows that the
average energy of the particles has increased
for the Y curve, indicating a higher
temperature.
Your answer
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D
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5.
Samples of 1-chlorobutane, 1-bromobutane and 1-iodobutane are put into separate
test tubes containing silver nitrate solution and then simultaneously placed into a
warm water bath.
In what order are the coloured precipitates observed?
A
white, cream then yellow
The learner has the correct order of the
precipitate colour as you go down the group,
but the order of precipitate formation is
reversed.
B
cream, yellow then white
The learner is either unsure of the colours of
each silver halide precipitate, or the trend in
hydrolysis rate down the group (or both).
C
cream, white then yellow
The learner is either unsure of the colours of
each silver halide precipitate, or the trend in
hydrolysis rate down the group (or both).
D
yellow, cream then white
Correct answer: The order of the
precipitates is iodide, bromide then chloride
due to the decreasing strength of the carbon–
halogen bond as you go down the group.
Your answer
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D
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6.
What is the role of the hydroxide ion in the reaction between aqueous sodium
hydroxide and bromopropane?
A
base
The hydroxide ion is commonly seen acting
as a base and learners often confuse the
action of a base with the action of a
nucleophile, especially since both involve
donation of the lone pair.
B
electrophile
The learner has confused the definitions of
electrophile and nucleophile.
C
free radical
The learner is perhaps associating the
reactions of haloalkanes with free radical
mechanisms, since they are involved in the
stratospheric depletion of ozone.
D
nucleophile
Correct answer: The hydroxide attacks the
positively polarised carbon of the C–Hal
bond.
Your answer
7.
D
The bond dissociation enthalpy for a carbon–chlorine bond is approximately
330 kJ mol–1.
What is the minimum frequency of light required to break one carbon–chlorine bond?
A
4.9 × 1038 Hz
This frequency corresponds to the energy
needed to break an entire mole of bonds; the
candidate has not used Avogadro’s number.
B
8.2 × 1014 Hz
Correct answer: The energy in kJ mol–1 must
be converted to energy in joules and then
applied to the Planck’s constant equation.
C
8.2 × 1011 Hz
The learner has not converted kilojoules to
joules.
D
1.2 × 10–15 Hz
The learner has calculated the correct energy
per bond but has inverted the rearrangement
of the Planck’s constant equation resulting in
a nonsensical answer.
Your answer
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B
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8.
Which reaction is a stage necessary for the formation of ozone in the stratosphere?
A
O3 + UV  O2 + O
This equation represents the way in which
ozone absorbs UV light in the stratosphere,
preventing it from reaching the lower
atmosphere.
B
O2 + UV  2O
Correct answer: Ozone is formed in two
stages – in the second stage the oxygen
radical formed in this reaction reacts with an
oxygen molecule to form O3.
C
O3 + Cl  O2 + ClO
This is a stage in the depletion of ozone, not
its formation.
D
ClO + O–  O2 + Cl–
This is a stage in the depletion of ozone, not
its formation.
Your answer
9.
B
Chlorine radicals in the stratosphere act as catalysts for the reaction shown below.
O3 + O  2O2
Which statement is true about the action of the chlorine radicals?
A
They increase the number of
collisions between ozone
molecules and oxygen molecules.
This is a common misconception amongst
learners, that catalysts are able to somehow
increase the number of collisions between
reactant particles.
B
They act as heterogeneous
catalysts.
Many gaseous reactions are catalysed by
heterogeneous catalysts; however, this is not
one of them as the chlorine radicals are also
in the gas state.
C
They are not used up during the
process.
Correct answer: Chlorine radicals are
reactants in the first step of ozone depletion
but reformed in the second step as products.
D
They increase the energy of the
collisions.
Only by increasing temperature can the
energy of the reactant particles be increased.
Your answer
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C
Copyright © OCR 2015
10.
Which of the following statements can explain why the rate of a reaction increases in
the presence of a suitable catalyst?
1.
A greater proportion of reactant particles have sufficient energy to react.
2.
Reactant particles collide with more energy.
3.
Reactant particles collide more frequently.
A
1, 2 and 3
The learner has confused the effect of a
catalyst with that of raising temperature.
B
only 1 and 2
The learner is confused about the reason that
more particles have enough energy to react
and assumes they have more energy.
C
only 2 and 3
The learner is choosing the most familiar
answers – again, ones which are often
encountered as an explanation for an
increase in temperature.
D
only 1
Correct answer: The catalyst provides an
alternate route with lower activation enthalpy,
meaning more particles have sufficient
energy for collisions to produce the minimum
energy needed to react.
Your answer
D
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Multiple choice practice test
The Ozone Story
Learner Activity
1.
Which molecule is polar?
A
BF3
B
CO2
C
NH3
D
SO3
Your answer
2.
What intermolecular forces are present between molecules of methanal, HCHO?
A
instantaneous dipole–induced dipole bonds only
B
hydrogen bonds and instantaneous dipole–induced dipole bonds
C
permanent dipole–permanent dipole bonds only
D
permanent dipole–permanent dipole bonds and instantaneous dipole–induced
dipole bonds
Your answer
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Copyright © OCR 2015
3.
Hydrofluoroalkanes, such as CH2F2, have been considered as an alternative to
CFCs.
Why are hydrofluoroalkanes preferable compounds?
A
They do not have as high a greenhouse factor.
B
They break down in the troposphere and do not reach the stratosphere, so do not
damage the ozone layer.
C
The bonds are not broken by UV radiation in the stratosphere, so they do not
cause ozone depletion.
D
They are less flammable and less toxic.
Your answer
4.
The Maxwell–Boltzmann distribution of energy for gaseous particles under two
different sets of conditions, X and Y, is shown below.
Which statement can be deduced from the distribution?
A
Y is at a lower concentration than X.
B
X and Y are at different pressures.
C
Y is in the presence of a catalyst.
D
Y is at a higher temperature than X.
Your answer
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5.
Samples of 1-chlorobutane, 1-bromobutane and 1-iodobutane are put into separate
test tubes containing silver nitrate solution and then simultaneously placed into a
warm water bath.
In what order are the coloured precipitates observed?
A
white, cream then yellow
B
cream, yellow then white
C
cream, white then yellow
D
yellow, cream then white
Your answer
6.
What is the role of the hydroxide ion in the reaction between aqueous sodium
hydroxide and bromopropane?
A
base
B
electrophile
C
free radical
D
nucleophile
Your answer
7.
The bond dissociation enthalpy for a carbon–chlorine bond is approximately
330 kJ mol–1.
What is the minimum frequency of light required to break one carbon–chlorine bond?
A
4.9 × 1038 Hz
B
8.2 × 1014 Hz
C
8.2 × 1011 Hz
D
1.2 × 10–15 Hz
Your answer
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8.
Which reaction is a stage necessary for the formation of ozone in the stratosphere?
A
O3 + UV  O2 + O
B
O2 + UV  2O
C
O3 + Cl  O2 + ClO
D
ClO + O–  O2 + Cl–
Your answer
9.
Chlorine radicals in the stratosphere act as catalysts for the reaction shown below.
O3 + O  2O2
Which statement is true about the action of the chlorine radicals?
A
They increase the number of collisions between ozone molecules and oxygen
molecules.
B
They act as heterogeneous catalysts.
C
They are not used up during the process.
D
They increase the energy of the collisions.
Your answer
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10.
Which of the following statements can explain why the rate of a reaction increases in
the presence of a suitable catalyst?
1.
A greater proportion of reactant particles have sufficient energy to react.
2.
Reactant particles collide with more energy.
3.
Reactant particles collide more frequently.
A
1, 2 and 3
B
only 1 and 2
C
only 2 and 3
D
only 1
Your answer
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