DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ2.19a

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.hl.TZ2.19a
Level hl Paper 3 Time zone TZ2
Command term Outline Question number a Adapted from N/A
a.
[Maximum mark: 3]
19M.3.hl.TZ2.19a

Electricity can be generated in a variety of ways.

(a)

Outline how a microbial fuel cell produces an electric current from glucose.

C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l)

[3]

Markscheme

Any three of:
C6H12O6 (aq) + 6H2O (l) → 6CO2 (g) + 24H+ (aq) + 24e–
OR
electrons released by oxidation of glucose [✔]

enzymes «in bacteria» oxidize glucose
OR
«bacteria» transfer «released» electrons directly to anode [✔]

24H+ (aq) + 6O2 (g) + 24e– → 12H2O (l)
OR
electrons consumed by reduction of oxygen [✔]


PEM/membrane separates two half reactions
OR
PEM/membrane allows proton/H+ transfer from anode to cathode [✔]

electrons flow though external circuit [✔]

 

Note: Accept 4H+ (aq) + O2 (g) + 4e– → 2H2O (l).

Examiners report

The question on microbial cell invited varied responses. Half equations for the oxidation of glucose or reduction of oxygen were rarely written. PEM/membrane separates two half- reactions and allows proton transfer from anode to cathode was missed by most of the candidates.

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