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AS & A Level CHEMISTRY 9701/51 Paper 5 Planning, Analysis and Evaluation May/June 2023 Authentic Marking Scheme $10.58
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AS & A Level CHEMISTRY 9701/51 Paper 5 Planning, Analysis and Evaluation May/June 2023 Authentic Marking Scheme
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AS & A Level CHEMISTRY 9701/51 Paper 5 Planning, Analysis and Evaluation May/June 2023 Authentic Marking Scheme

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  • April 11, 2024
  • 24
  • 2023/2024
  • Exam (elaborations)
  • Questions & answers

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  • as a level chemistry 970151 paper 5

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  • A/AS Level
  • OCR
  • chemistry
  • Chemistry
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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.


DC (LK/SG) 309546/6
© UCLES 2023 [Turn over

, 2

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.

[HOOCCH2CH2COOH(ethoxyethane)]
Kpc =
[HOOCCH2CH2COOH(aq)]

[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.

stopper

separating funnel




tap




Fig. 1.1




© UCLES 2023 9701/51/M/J/23

, 3

(a) (i) State whether beaker A in step 7 contains the aqueous layer or the ethoxyethane layer.

Explain your answer.

Beaker A contains the ................................................. layer.

explanation ........................................................................................................................

...........................................................................................................................................
[1]

(ii) Identify the piece of apparatus that should be used in step 8 to transfer 10.0 cm3 of the
aqueous layer.

..................................................................................................................................... [1]

(iii) Suggest why water is added to the ethoxyethane layer in step 9 before the titration can
take place.

...........................................................................................................................................

..................................................................................................................................... [1]




© UCLES 2023 9701/51/M/J/23 [Turn over

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