DP Chemistry (last assessment 2024)

Question 20N.2.hl.TZ0.5c

Date	November 2020	Marks available	[Maximum mark: 1]	Reference code	20N.2.hl.TZ0.5c
Level	hl	Paper	2	Time zone	TZ0
Command term	State	Question number	c	Adapted from	N/A

[Maximum mark: 1]

20N.2.hl.TZ0.5c

A student performs a titration to determine the concentration of ethanoic acid, ${CH}_{3} COOH$ , in vinegar using potassium hydroxide.

(c)

State the $K_{a}$ expression for ethanoic acid.

[1]

Markscheme

$K_{a} = \frac{[{CH}_{3} {COO}^{-}] [H_{3} O^{+}]}{[{CH}_{3} COOH]}$

Accept $H^{+}$ instead of $H_{3} O^{+}$ .

Examiners report

Poorly answered with only 50% correctly writing a K_a expression. The major error was in candidates trying to calculate a K_a rather than write an expression for it.

Syllabus sections

Core

Core » Topic 8: Acids and bases » 8.2 Properties of acids and bases

Core » Topic 7: Equilibrium » 7.1 Equilibrium

Core » Topic 7: Equilibrium

Core » Topic 8: Acids and bases

Question 20N.2.hl.TZ0.5c

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