CAIE A Level 9701

Chemistry 2020 · Oct/Nov

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This CAIE A Level Chemistry paper focuses mainly on practical chemistry skills, especially rates of reaction and qualitative analysis of ions. Students can expect structured experimental questions involving plotting graphs, handling anomalous results, using proportional relationships, calculating rates and times, and explaining how concentration affects reaction rate, as well as test-tube chemistry for identifying cations and anions from observations.…

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Questions & Model Answers 15 Qs

Q1b
Structured 3 marks
On the grid opposite, plot a graph of rate of reaction (y-axis) against volume of FA 1 (x-axis). Include the origin, (0,0), in your scales. Circle any points you consider anomalous and draw a line of best fit.
Plot the graph of rate of reaction against volume of FA 1, including the origin, circle any anomalous points, and draw a line of best fit.
This is a graph-plotting task; the correct response is the completed graph meeting the stated requirements.
Q1c
Short Answer 2 marks
Use your graph to calculate the time that the reaction would have taken if 5.00 cm3 of FA 1 had been used. Show on the graph how you obtained your answer. time = .............................. s
Read the rate from the graph at 5.00 cm3 of FA 1, then use rate = 1000 / reaction time to calculate the time.
The time must be obtained from the graph and the given rate equation.
Q1d(i)
Short Answer 2 marks
Using data from Experiments 1 and 2, show by calculation that the volume of aqueous potassium iodide, FA 1, used was directly proportional to the concentration of iodide ions.
Show that the ratio of volume of FA 1 to concentration of iodide ions is constant for Experiments 1 and 2, so volume is directly proportional to concentration.
Direct proportionality is demonstrated by a constant ratio between the two quantities.
Q1d(ii)
Short Answer 2 marks
Explain, by referring to your graph or your table of results, how the rate of reaction is affected by an increase in the concentration of aqueous potassium iodide, FA 1.
As the concentration of aqueous potassium iodide increases, the rate of reaction increases.
A higher concentration gives more frequent successful collisions, increasing the rate.
Q1e(i)
Short Answer 1 mark
Write an ionic equation for the reaction between thiosulfate ions and hydrogen ions in aqueous solution. Include state symbols.
S2O3^2-(aq) + 2H+(aq) -> S(s) + SO2(g) + H2O(l)
This is the balanced ionic equation for thiosulfate reacting with acid.
Q1e(ii)
Short Answer 1 mark
A student carries out the same investigation as in (a) but the solutions are mixed in a different order. The student places FA 1 and an appropriate volume of distilled water in one beaker and all the other reactants in a second beaker. The student then transfers the mixture from the second beaker to the first and starts timing. Tick the box for the statement you consider correct. Explain your answer. The student's method is better than that in (a). The two methods are equally good. The student's method is not as good as that in (a). reason
The student's method is not as good as that in (a), because the reaction starts before the solutions are fully mixed and timing may be less accurate.
The original method is better because it allows timing to start at a more consistent point.
Q1f(i)
Short Answer 2 marks
Another student investigates the effect of iron(III) concentration on the rate of this reaction. The student carries out another experiment, Experiment 6, and the rate is compared to that of Experiment 2. In Experiment 2, the volumes used were: reagent volume / cm3 FA 1 10.00 FA 2 10.0 FA 3 20.0 FA 4 10.0 distilled water 10.00 Suggest the volumes the student could use for Experiment 6.
Use the same total volume as Experiment 2, but change the volume of FA 4 to alter the iron(III) concentration and adjust distilled water accordingly.
To investigate only iron(III) concentration, all other volumes should be kept constant except FA 4 and water.
Q1f(ii)
Short Answer 1 mark
This student records a time of 178 s for Experiment 2. The rate of reaction is directly proportional to the concentration of iron(III) ions. Suggest how long it would take the reaction mixture proposed for Experiment 6 in (f)(i) to turn blue-black. Assume that Experiment 6 is carried out at the same temperature as Experiment 2. Do not carry out Experiment 6. time = .............................. s
Use the direct proportionality between rate and iron(III) concentration to scale the time inversely with concentration.
If rate increases, the time taken decreases in inverse proportion.
Q2a(i)
Short Answer 3 marks
FA 5 is a salt consisting of two ions both of which are listed in the Qualitative Analysis Notes. Place a small spatula measure of FA 5 into a hard-glass test-tube. Heat the tube gently at first and then more strongly. Record all your observations.
Record the observations made on heating FA 5, including any colour change, gas evolved, and residue formed.
This is an observation-based qualitative analysis question.
Q2a(ii)
Short Answer 2 marks
FA 6 is a sample of the residue obtained from FA 5 after strong heating. Place a small spatula measure of FA 6 in a test-tube and add a 1 cm depth of aqueous hydrogen peroxide. Record your observations.
Record the observations when aqueous hydrogen peroxide is added to FA 6, including any effervescence, colour change, or gas produced.
The answer depends on the observed reaction of the residue with hydrogen peroxide.
Q2a(iii)
Short Answer 2 marks
Dissolve a spatula measure of FA 5 in a 5 cm depth of distilled water in a boiling tube. Use separate 1 cm depths of this solution in test-tubes for the following tests. Record your observations. Keep the remainder of FA 5(aq) for use in 2(b)(ii). Test 1 Add aqueous sodium hydroxide. Test 2 Add a 1 cm depth of aqueous hydrogen peroxide, then add aqueous sodium hydroxide.
Record the observations for FA 5(aq) with aqueous sodium hydroxide and with hydrogen peroxide followed by sodium hydroxide.
These are qualitative test observations used to identify the cation.
Q2b(i)
Short Answer 2 marks
FA 7 is a solution of a different salt. The cation present in FA 7 is not listed in the Qualitative Analysis Notes. FA 5(aq) and FA 7 each contain either a halide ion or an anion containing sulfur. These anions are listed in the Qualitative Analysis Notes. For both of these anions, select reagents that you would use in order to carry out tests that give positive results. Record the reagents and the ions for which they would test.
Use aqueous silver nitrate for halide ions, and aqueous barium ions with dilute acid for sulfate or sulfite ions.
These are standard confirmatory tests for halides and sulfur-containing anions.
Q2b(ii)
Short Answer 3 marks
Carry out both of your tests on FA 5(aq) and FA 7 and record your results in the space below.
Record the results of the selected anion tests on FA 5(aq) and FA 7.
The results depend on the actual ions present in the samples.
Q2b(iii)
Short Answer 2 marks
Use your observations in (a) and (b)(ii) to identify the ions present in FA 5 and FA 7. Write the formula of each ion in the table. If the tests you carry out do not allow you to identify any of the ions, write 'unknown'. FA 5 FA 7 cation anion
Identify the cation and anion in FA 5 and FA 7 from the qualitative test results, or write unknown where identification is not possible.
The ions must be inferred from the observations in the earlier tests.
Q2b(iv)
Short Answer 2 marks
Suggest what you would observe if you added aqueous chlorine to separate portions of aqueous solutions of FA 5 and FA 7. Do not carry out this test. aqueous chlorine and FA 5(aq) aqueous chlorine and FA 7(aq)
State the expected observations when aqueous chlorine is added to FA 5(aq) and FA 7(aq), based on halide displacement or oxidation of sulfur-containing anions.
The observation depends on the ions identified in the samples.
Paper Details
Board CAIE
Level A Level
Subject Chemistry
Code 9701
Year 2020
Session Oct/Nov
Q&A 15 questions
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