DP Chemistry (last assessment 2024)

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Question 22M.2.hl.TZ1.d

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Date May 2022 Marks available [Maximum mark: 2] Reference code 22M.2.hl.TZ1.d
Level hl Paper 2 Time zone TZ1
Command term Comment Question number d Adapted from N/A
d.
[Maximum mark: 2]
22M.2.hl.TZ1.d

Ammonia is soluble in water and forms an alkaline solution:

NH3 (g) + H2O (l) ⇌ NH4+ (aq) + HO– (aq)

Magnesium salts form slightly acidic solutions owing to equilibria such as:

Mg2+ (aq) + H2O (l) ⇌ Mg(OH)+ (aq) + H+ (aq)

Comment on the role of Mg2+ in forming the Mg(OH)+ ion, in acid-base terms.

[2]

Markscheme

Lewis acid ✔

accepts «a lone» electron pair «from the hydroxide ion» ✔

 

Do not accept electron acceptor without mention of electron pair.

Examiners report

Mediocre performance; although some Mg2+ was identified as a Lewis acid, the reasoning given was that it accepts an electron, rather than an electron pair or references were made to Bronsted-Lowry theory.

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