Chemistry · May / June 2023 · Paper 61 · Question 2
0620
As printed in the paper
The question as text
A student investigates the reaction between aqueous ammonia and two different aqueous solutions of copper(II) sulfate labelled A and B. Solutions A and B have different concentrations. The student does two experiments. Experiment 1 ● Fill a burette with solution A. ● Run some of solution A out of the burette so that the level of solution A is on the burette scale and record the initial burette reading. ● Use a measuring cylinder to pour 25 cm3 of aqueous ammonia into a conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution A 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 ● Empty the conical flask and rinse it with distilled water. ● Empty the burette and rinse it with distilled water. ● Rinse the burette with solution B. ● Repeat Experiment 1 using solution B instead of solution A.
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
2(a)[4]
M1 final and initial burette reading for experiment 1 correct (18.3 and 0.6)
M2 final and initial burette reading for experiment 2 correct (21.0 and 9.2)
M3 both titres correct 17.7 and 11.8)
M4 all volumes recorded consistently to 1 dp or better
2(b)[1]
to make solid easier to see / so colour (change) easier to see
2(c)(i)[1]
to clean / remove solution A
2(c)(ii)[1]
to remove water
2(c)(iii)[2]
M1 more solution B needed
M2 as more (than 25 cm3 of) aqueous ammonia in flask
2(d)(i)[1]
solution B
and
as a smaller volume was needed / smaller titre
2(d)(ii)[1]
1.5, ecf from results
2(e)[1]
repeat experiment
and
compare
2(f)[2]
M1 7.1 or calculated value of titre in experiment 1 ÷ 2.5
M2 cm3
2(g)[2]
advantage: (more) accurate
disadvantage: slower / takes longer
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