Chemistry · May / June 2024 · Paper 62 · Question 2
0620
As printed in the paper
The question as text
A student investigates the reaction between aqueous aluminium chloride and two aqueous solutions of sodium hydroxide, solution F and solution G. Solution F and solution Ghavedierent concentrations. The student does three experiments. Experiment 1 Rinse a burette with distilled water and then with aqueous aluminium chloride. Rinse a conical flask with distilled water. Fill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. Record the initial burette reading. Use a measuring cylinder to pour 25 cm3 of solution F into the conical flask. Stand the conical flask on a black or dark-coloured sheet of paper. Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the mixture in the conical flask just starts to become cloudy. Record the final burette reading. Experiment 2 Refill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. Record the initial burette reading. Rinse the conical flask with distilled water. Rinse the measuring cylinder with distilled water and then with solution G. Use the measuring cylinder to pour 25 cm3 of solution G into the conical flask. Stand the conical flask on a black or dark-coloured sheet of paper. Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the mixture in the conical flask just starts to become cloudy. Record the final burette reading. Experiment 3 Refill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. Record the initial burette reading. Rinse the conical flask with distilled water. Use the measuring cylinder to pour 25 cm3 of solution G into the conical flask. Add 5 drops of thymolphthalein indicator to the conical flask. Stand the conical flask on a white tile. Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the thymolphthalein indicator changes colour. Record the final burette reading.
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Show the answer and mark scheme
2(a)[4]
M1 all three final readings recorded correctly (14.7, 29.5, 28.0)
M2 all three initial readings recorded correctly (1.3, 2.7, 0.4)
M3 all three titres correct (13.4, 26.8, 27.6)
M4 all volumes recorded to 1 d.p. or better
2(b)[1]
(from) blue (to) colourless
2(c)[1]
to mix (reactants)
2(d)[1]
(white) precipitate / cloudiness easier to see
2(e)(i)[1]
to clean / to remove solution F
2(e)(ii)[1]
same solution (of NaOH) used / used for solution G in both
2(f)[3]
M1 solution G is more concentrated
M2 as larger volume (of AlCl3(aq)) required (in Experiment 2)
M3 quantitative relationship such as:
twice as concentrated OR needed twice as much aluminium chloride
2(g)[2]
M1 5.36 / 5.4
M2 cm3
2(h)[1]
volume used is not fixed / volume needed is not the same in each experiment.
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