Cambridge International AS & A Level
* 3 8 4 7 2 5 6 0 9 7 *
CHEMISTRY 9701/51
Paper 5 Planning, Analysis and Evaluation May/June 2023
1 hour 15 minutes
You must answer on the question paper.
No additional materials are needed.
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
● The total mark for this paper is 30.
● The number of marks for each question or part question is shown in brackets [ ].
● The Periodic Table is printed in the question paper.
● Important values, constants and standards are printed in the question paper.
This document has 16 pages. Any blank pages are indicated.
1 The partition coefficient, Kpc, shows the distribution of a solute between two immiscible solvents.
Kpc is determined by measuring the concentration of the solute in each solvent.
The organic solvent ethoxyethane, CH3CH2OCH2CH3, and water are immiscible. A student is
asked to find Kpc of butanedioic acid, HOOCCH2CH2COOH, between ethoxyethane and water.
The expression for Kpc when butanedioic acid is in equilibrium between ethoxyethane and water is
shown.
[density: ethoxyethane, 0.71 g cm–3; water, 1.00 g cm–3]
The student uses the following method to find the partition coefficient. A diagram of the apparatus
is shown in Fig. 1.1.
step 1 Add 30.0 cm3 of distilled water to a separating funnel.
step 2 Weigh by difference 2.81 g of butanedioic acid into the separating funnel.
step 3 Stopper the separating funnel and shake it until the butanedioic acid has dissolved.
step 4 Remove the stopper and add 30.0 cm3 of ethoxyethane to the separating funnel.
step 5 Replace the stopper and shake the separating funnel gently.
step 6 Place the separating funnel into a clamp. Allow the liquids to settle so that the two layers
can be seen.
step 7 Remove the stopper and open the separating funnel tap to allow the lower layer to run
into a beaker labelled A. Run the upper layer into a beaker labelled B.
step 8 Transfer 10.0 cm3 of the aqueous layer into a conical flask. Titrate with 0.500 mol dm–3
NaOH(aq). Use thymolphthalein as the indicator.
step 9 Take 10.0 cm3 of the ethoxyethane layer and add 10.0 cm3 of water to it. Titrate this
mixture with 0.100 mol dm–3 NaOH(aq). Use thymolphthalein as the indicator.
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