Instructions and answers for teachersThese 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 ActivityThis 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 OutcomesThis 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).
IntroductionMultiple 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:
Multiple Choice Questions (MCQ) topic quiz - answers1. 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.
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. 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.
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.
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.
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 The forward reaction rate exceeds the reverse reaction rate.
Correct answer: The mixture started with 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.
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.
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.
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This formative assessment resource has been produced as part of our free Chemistry teaching and learning support package. All the Chemistry teaching and learning resources, including delivery guides, topic exploration packs, lesson elements and more are available on the qualification webpages.
If you are looking for examination practice materials, you can find Sample Assessment Materials (SAMs) and a link to the Practice Papers on the qualification webpages: Chemistry A, Chemistry B.
10. Which of the following statements is/are true of the sulfur compounds formed when solid potassium bromide is reacted with concentrated sulfuric acid?
