DP Chemistry (first assessment 2025)

Question 20N.2.SL.TZ0.b(ii)

Date	November 2020	Marks available	[Maximum mark: 2]	Reference code	20N.2.SL.TZ0.b(ii)
Level	SL	Paper	2	Time zone	TZ0
Command term	Write	Question number	b(ii)	Adapted from	N/A

b(ii).

[Maximum mark: 2]

20N.2.SL.TZ0.b(ii)

Pure magnesium needed for making alloys can be obtained by electrolysis of molten magnesium chloride.

Write the half-equations for the reactions occurring in this electrolysis.

[2]

Markscheme

Anode: $2 {Cl}^{-} \to {Cl}_{2} (g) + 2 e^{-}$ ✔

Cathode: ${Mg}^{2 +} + 2 e^{-} \to Mg (l)$ ✔

Accept $C l^{-} \to C l_{2} (g) + e^{-}$ .

Award [1 max] for correct equations at incorrect electrodes.

Examiners report

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.6—A primary (voltaic) cell is an electrochemical cell that converts energy from spontaneous redox reactions to electrical energy. Explain the direction of electron flow from anode to cathode in the external circuit, and ion movement across the salt bridge.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.8—An electrolytic cell is an electrochemical cell that converts electrical energy to chemical energy by bringing about non-spontaneous reactions. Explain how current is conducted in an electrolytic cell. Deduce the products of the electrolysis of a molten salt.

Question 20N.2.SL.TZ0.b(ii)

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