DP Chemistry (last assessment 2024)

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Question 21M.2.hl.TZ1.b

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Date May 2021 Marks available [Maximum mark: 3] Reference code 21M.2.hl.TZ1.b
Level hl Paper 2 Time zone TZ1
Command term Sketch Question number b Adapted from N/A
b.
[Maximum mark: 3]
21M.2.hl.TZ1.b

Propanoic acid, CH3CH2COOH, is a weak organic acid.

Sketch the general shape of the variation of pH when 50 cm3 of 0.001 mol dm–3 NaOH (aq) is gradually added to 25 cm3 of 0.001 mol dm–3 CH3CH2COOH (aq).

[3]

Markscheme

Any three of:

correct “S” shape ✔

equivalence point at 25 cm3 ✔

final pH tends to 11 ✔

pH at equivalence point >7 ✔

starting pH between 3.8 - 4 ✔

pH at half equivalence approx. 5 ✔


Do not penalize for incorrect points.
Award any 3 correct.

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