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Date May 2017 Marks available 1 Reference code 17M.2.sl.TZ2.7
Level SL Paper 2 Time zone TZ2
Command term Calculate Question number 7 Adapted from N/A

Question

Soluble acids and bases ionize in water.

Sodium hypochlorite ionizes in water.

OCl(aq) + H2O(l) OH(aq) + HOCl(aq)

A solution containing 0.510 g of an unknown monoprotic acid, HA, was titrated with 0.100 mol dm–3 NaOH(aq). 25.0 cm3 was required to reach the equivalence point.

Identify the amphiprotic species.

[1]
a.i.

Identify one conjugate acid-base pair in the reaction.

[1]
a.ii.

Calculate the amount, in mol, of NaOH(aq) used.

[1]
b.i.

Calculate the molar mass of the acid.

[1]
b.ii.

Calculate [H+] in the NaOH solution.

[1]
b.iii.

Markscheme

water/H2O

Accept “hydroxide ion/OH”.

[1 mark]

a.i.

[1 mark]

a.ii.

«0.100 mol dm–3 x 0.0250 dm3» = 0.00250 «mol»

[1 mark]

b.i.

«M = 0.510  g 0.00250  mol  =» 204 «g mol–1»

[1 mark]

b.ii.

«1.00 x 10–14 = [H+] x 0.100»

1.00 x 10–13 «mol dm–3»

[1 mark]

b.iii.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
b.iii.

Syllabus sections

Core » Topic 8: Acids and bases » 8.1 Theories of acids and bases
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Core » Topic 1: Stoichiometric relationships » 1.3 Reacting masses and volumes
Core » Topic 1: Stoichiometric relationships
Core » Topic 8: Acids and bases
Core

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