Chemistry 2020 May/June | Past Paper

Q1

MCQ 1 mark

A student plans to carry out an experiment to find the relative molecular mass, M , of a soluble acidic gas, X, by finding the mass of a measured volume of gas X. Gas X can be prepared by the reaction between concentrated sulfuric acid and copper. Two methods of gas collection are available to the student, as shown. heat concentrated sulfuric acid measuring cylinder method A method B water water trough beehive shelf copper turnings heat concentrated sulfuric acid copper turnings gas Xgas syringe clamp

A

student plans to carry out an experiment to find the relative molecular mass, M

A

method B

Q1(a)

Short Answer 1 mark

(i) Explain why the first sample of gas collected from either apparatus should not be used for the M determination of gas X.

Q1(ii)

Short Answer 2 marks

Give two reasons, other than your answer to (a)(i), why, for this experiment, the apparatus in method A is less suitable than the apparatus in method B for collecting a sample of gas X. reason 1 . reason 2 .

Q1(b)

Short Answer 1 mark

The student is told to use the U-tube shown to find the mass of a sample of gas X. gas X gas syringe U-tube soda lime sample of pure gas X is placed in a gas syringe. The gas syringe is attached to a U-tube containing small lumps of solid soda lime, a mixture of sodium hydroxide and calcium hydroxide. All of gas X is slowly passed into the U-tube and the mass of gas X absorbed determined. The temperature and the pressure of the room are recorded.

Q1(i)

Short Answer 1 mark

State the measurements that are needed to determine the mass of gas X absorbed.

Q1(ii)

Short Answer 1 mark

Suggest why soda lime is used to absorb gas X.

Q1(c)

Short Answer 1 mark

Gas X can cause respiratory distress. State an appropriate precaution that should be taken when doing this experiment. of pure gas X.

Q1(i)

Short Answer 1 mark

Calculate the number of moles of gas X present in Experiment 1. You should assume that gas X behaves like an ideal gas and so use PV = nRT . moles of gas X = mol [2] Explain how the student should use this information and their results to determine the M of X.

Q1(iii)

Short Answer 1 mark

Not all of gas X is absorbed by the soda lime. State what effect, if any, this has on the student's calculated value of the M of gas X.

Q1(iv)

Short Answer 1 mark

In Experiment 2, the same mass of gas X is used, but the student did not record the temperature and pressure. The calculated M of X for Experiment 2 is higher than the value calculated by the student for Experiment 1. State and explain how the value of changes from Experiment 1 to Experiment 2.

Q1(e)

Short Answer 1 mark

State how the reliability of the results in Experiment 1 could be improved.

Q1(f)

Short Answer 1 mark

A different gas, methylamine, is alkaline. State a change that would have to be made to the apparatus so that the M of methylamine could be determined. [Total: 13]

Q2

Short Answer 1 mark

Each student in a class of nine students performs an experiment to find the formula of a chloride of iron. Each student prepares the chloride of iron by passing a stream of chlorine gas over a sample of iron wire as shown in the diagram. dry chlorine gas excess chlorine gas heat chloride of iron iron wire

Q2(a)

Short Answer 1 mark

Each student carries out the following steps in the order shown in the list. Some of the measurement steps are missing from the list.

Q2(i)

Short Answer 1 mark

State the two additional measurement steps that each student must perform in order to find the formula of the chloride of iron. 1 2

Q2(ii)

Short Answer 1 mark

The flow of dry chlorine gas must start before the iron wire is heated. Explain why.

Q2(iii)

Short Answer 1 mark

State an assumption that has to be made for the measurements made in this experiment to be valid.

Q2(b)

Short Answer 3 marks

(i) The class results are shown in the table. student mass of iron wire mass of iron chloride mass of chlorine amount of iron amount of chlorine atoms 1 0.57 1.64 2 1.10 3.16 3 1.40 4.03 4 1.95 5.61 5 2.18 5.89 6 2.75 7.90 7 3.05 8.77 8 3.45 9.80 9 3.90 11.18 Calculate the mass of chlorine that reacts with the iron wire in each experiment. Record each mass to two decimal places. Calculate the amount of iron, in mol, and amount of chlorine atoms, in mol, that reacts in each experiment. Record the number of moles to three significant figures. : Fe, 55.8; C l, 35.5]

Q2(ii)

Short Answer 1 mark

Plot a graph on the grid of the amount of chlorine atoms against the amount of iron. Use a cross ( ×) to plot each data point. Draw a line of best fit through the plotted points. You should consider whether (0,0) should be on the line of best fit. [2] 0.00 0.01 0.02 0.03 0.04 amount of iron / mol amount chlorine atoms / mol 0.05 0.06 0.07 0.08 0.22 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00

Q2(iii)

Short Answer 1 mark

Circle the point on the graph you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure.

Q2(c)

Short Answer 1 mark

Use the graph to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be on your line of best fit. Give your answer to three significant figures . coordinates 1 coordinates 2 gradient = [2] State how the results student 4 obtains could be used to determine this formula.

Q2(e)

Short Answer 1 mark

(i) Student 3 weighs the conical flask using a balance accurate to two decimal places and Calculate the percentage error in measuring the mass of this chloride of iron. percentage error = %

Q2(ii)

Short Answer 1 mark

Student 8 follows the same procedure as student 3. State whether the results from student 8 will have more or less percentage error than those from student 3. Explain your answer.

Q2(f)

Short Answer 1 mark

Another student suggested that the chloride of iron could also be prepared by the reaction between iron wire and hydrochloric acid.

Q2(i)

Short Answer 1 mark

A sample of a chloride of iron prepared in this way contains 44% iron by mass. : Fe, 55.8; C l, 35.5]

Q2(ii)

Short Answer 1 mark

Explain, using the electrode potential values in the table, why the methods in

Q2(ii)(f)

Short Answer 1 mark

do not produce the same chlorides of iron. reaction electrode potential, E

Q2(aq)

Short Answer 1 mark

+ 2e Fe

Q2(aq)(s)

Short Answer 1 mark

-0.44

Q2(aq)

Short Answer 1 mark

+0.77 [Total: 17] Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Cambridge Local Examinations Syndicate (UCLES), which itself is a department of the University of Cambridge.

Board	CAIE
Level	A Level
Subject	Chemistry
Code	`9701`
Year	2020
Session	May/June
Q&A	30 questions

Chemistry 2020 · May/June

Questions & Model Answers 30 Qs

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