Exam (elaborations)
AS & A Level CHEMISTRY9701/35 Paper 3 Advanced Practical Skills 1 May/June 2023 Authentic Marking Scheme
AS & A Level CHEMISTRY9701/35 Paper 3 Advanced Practical Skills 1 May/June 2023 Authentic Marking Scheme
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Cambridge International AS & A Level* 2 1 7 0 3 8 0 4 7 7 *
CHEMISTRY 9701/35
Paper 3 Advanced Practical Skills 1 May/June 2023
2 hours
You must answer on the question paper.
You will need: The materials and apparatus listed in the confidential instructions
INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● You may use a calculator.
● You should show all your working and use appropriate units.
INFORMATION Session
● The total mark for this paper is 40.
● The number of marks for each question or part question is shown in
brackets [ ]. Laboratory
● The Periodic Table is printed in the question paper.
● Important values, constants and standards are printed in the
question paper.
● Notes for use in qualitative analysis are provided in the
question paper. For Examiner’s Use
1
2
3
Total
This document has 12 pages.
DC (LK/CB) 310969/3
© UCLES 2023 [Turn over
, 2
Quantitative analysis
Read through the whole method before starting any practical work. Where appropriate, prepare a table
for your results in the space provided.
Show the precision of the apparatus you used in the data you record.
Show your working and appropriate significant figures in the final answer to each step of your
calculations.
1 Magnesium is a reactive metal which corrodes when left in air. Magnesium reacts with acid to
release hydrogen.
You will determine the percentage purity of a sample of magnesium by reacting it with excess
hydrochloric acid and measuring the volume of hydrogen formed.
Mg(s) + 2HCl (aq) MgCl 2(aq) + H2(g)
FA 1 is hydrochloric acid, HCl .
FA 2 is magnesium, Mg.
(a) Method
● Weigh the container with FA 2. Record the mass.
● Fill the tub with water to a depth of approximately 5 cm.
● Fill the 250 cm3 measuring cylinder completely with water. Holding a piece of paper towel
firmly over the top, invert the measuring cylinder and place it in the water in the tub.
● Remove the paper towel and clamp the inverted measuring cylinder so the open end is
in the water just above the base of the tub.
● Use the 50 cm3 measuring cylinder to transfer 50.0 cm3 of FA 1 into the flask labelled X.
Check that the bung fits tightly into the neck of flask X, clamp flask X and place the end
of the delivery tube into the inverted 250 cm3 measuring cylinder.
● Remove the bung from the neck of the flask. Add all the FA 2 to the acid and replace the
bung immediately. Remove the flask from the clamp and swirl it to mix the contents.
● Replace the flask in the clamp. Leave for several minutes, swirling the flask occasionally.
● Weigh the empty container. Record the mass.
● Calculate and record the mass of FA 2 that is added to the acid.
Start Question 2 or Question 3 while the gas is being collected.
● When the reaction stops producing gas, record the final volume of gas collected.
I
II
III
volume of gas = ..................... cm3 [3]
© UCLES 2023 9701/35/M/J/23
, 3
(b) Calculations
(i) Calculate the amount, in mol, of hydrogen collected in the measuring cylinder at room
conditions.
amount of H2 = ................................. mol [1]
(ii) Use your answer to (b)(i) to deduce the amount, in mol, of magnesium that reacted in
your experiment.
amount of Mg = ...................................... mol
Hence calculate the percentage purity of the magnesium.
purity of Mg = ......................................... %
[2]
(c) A student carries out this practical procedure but uses magnesium powder rather than
magnesium ribbon. State the effect this would have on the percentage purity the student
calculates. Explain your answer.
...................................................................................................................................................
...................................................................................................................................................
............................................................................................................................................. [2]
(d) Another student investigates the reaction of a metal carbonate with hydrochloric acid by
measuring the change in mass during the reaction. The reaction is carried out in a beaker on
the pan of a balance.
(i) Explain why the mass displayed on the balance decreases during the reaction.
...........................................................................................................................................
..................................................................................................................................... [1]
(ii) Explain why using a balance to monitor the reaction between magnesium and
hydrochloric acid is not accurate.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(iii) Give the ionic equation for a solid carbonate, CO32–(s), reacting with hydrochloric acid.
Include state symbols.
..................................................................................................................................... [1]
[Total: 12]
© UCLES 2023 9701/35/M/J/23 [Turn over
, 4
2 In Question 1 you determined the percentage purity of a sample of magnesium by measuring the
volume of the gas produced when it reacts with an acid. In Question 2 you will use the enthalpy
change of the reaction between magnesium and hydrochloric acid to find the percentage purity.
This reaction is exothermic.
Mg(s) + 2HCl (aq) MgCl 2(aq) + H2(g)
FA 3 is hydrochloric acid, HCl . This is used in excess.
FA 4 is magnesium, Mg. You should assume it has a mass of 0.40 g.
(a) Method
● Support the cup in the 250 cm3 beaker.
● Rinse the 50 cm3 measuring cylinder with a little FA 3.
● Use the 50 cm3 measuring cylinder to transfer 25.0 cm3 of FA 3 into the cup.
● Place the thermometer in the acid and tilt the cup, if necessary, so that the bulb of the
thermometer is fully covered. Measure and record the temperature at time 0 minutes in
Table 2.1.
● Start timing and do not stop the clock until the whole experiment has been completed at
time 7 minutes.
● Record the temperature of FA 3 in the cup every 12 minute for 1 12 minutes.
● At time 2 minutes place FA 4 into the acid and stir the mixture.
● Record the temperature every 12 minute. Stir the mixture between thermometer readings.
Results
Table 2.1
1
time / minutes 0 2 1 1 12 2 2 12 3 3 12
temperature
X I
/ °C
II
time / minutes 4 4 12 5 5 12 6 6 12 7 III
temperature
/ °C
[3]
(b) (i) Plot a graph of temperature (on the y-axis) against time (on the x-axis) on the grid. The
scale for the y-axis should extend 15 °C above the maximum temperature you recorded.
Label any points you consider to be anomalous.
© UCLES 2023 9701/35/M/J/23
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