DP Chemistry (last assessment 2024)

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Question 19M.3.sl.TZ2.16b

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Date May 2019 Marks available [Maximum mark: 1] Reference code 19M.3.sl.TZ2.16b
Level sl Paper 3 Time zone TZ2
Command term Determine Question number b Adapted from N/A
b.
[Maximum mark: 1]
19M.3.sl.TZ2.16b

Excess acid in the stomach can cause breakdown of the stomach lining.

(b)

Some antacids contain carbonates.

Determine the pH of a buffer solution which contains 0.160 mol dm−3 CO32− and 0.200 mol dm−3 HCO3−, using section 1 of the data booklet.

pKa (HCO3−) = 10.32

[1]

Markscheme

«pH = pKa + log  [ A − ] [ HA] = 10.32 + log  0.160 0.200 = 10.32 – 0.097»

«pH =»10.22  [✔]

Examiners report

This was in general a well answered question. Most candidates who did not receive the mark inverted the concentration of the conjugate base/concentration of the acid in the calculation.

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