Multiple Choice Questions (MCQ) topic quiz
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 is a teaching and learning resource containing 10 multiple choice questions (MCQs) on the theme of the ozone story. 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 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 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:
The ozone story.
Version 1 1 © OCR 2016
Multiple Choice Questions (MCQ) topic quiz - 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 dot-and-cross diagrams, but the learner should appreciate that sulfur forms three double bonds and therefore the shape is symmetrical.
Your answer
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
3. Hydrofluoroalkanes, such as CH2F2, have been considered as an alternative to CFCs.
Why are hydrofluoroalkanes preferable compounds?
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
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
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
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. 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
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. 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
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
Version 1 9 © OCR 2016
Multiple Choice Questions (MCQ) topic quiz
The Ozone Story
Learner Activity
1. Which molecule is polar?
A / BF3B / CO2
C / NH3
D / SO3
Your answer
2. What intermolecular forces are present between molecules of methanal, HCHO?
A / instantaneous dipole–induced dipole bonds onlyB / 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
Version 1 9 © OCR 2016
3. Hydrofluoroalkanes, such as CH2F2, have been considered as an alternative to CFCs.
Why are hydrofluoroalkanes preferable compounds?
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
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 yellowB / 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 / baseB / 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 HzB / 8.2 × 1014 Hz
C / 8.2 × 1011 Hz
D / 1.2 × 10–15 Hz
Your answer
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.