DP Chemistry (last assessment 2024)

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Question 23M.3.HL.TZ1.13

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Date May 2023 Marks available [Maximum mark: 9] Reference code 23M.3.HL.TZ1.13
Level HL Paper 3 Time zone TZ1
Command term Deduce, Outline, Write Question number 13 Adapted from N/A
13.
[Maximum mark: 9]
23M.3.HL.TZ1.13

Biofuels can be synthesized or converted to make them more usable.

(a)

Write the equation for the fermentation of glucose, C6H12O6, to produce ethanol.

[1]

Markscheme

C6H12O6 → 2C2H5OH + 2CO2 ✓

(b)

Deduce the equation for the reaction of the triglyceride shown with methanol.

[2]

Markscheme

ester product ✓

glycerol AND correct balancing ✓

(c)

Outline the essential feature needed for a molecule to convert light energy into chemical energy. 

[1]

Markscheme

conjugated bonds/alternating C=C bonds/delocalized electrons/bonding ✓

 

Accept ‘alternating single and double bonds’.

Do not accept ‘many double bonds’.

(d)

The Geobacter bacterium anaerobically oxidizes substances present in the substrate of microbial fuel cells. For example, ethanoate ions, CH3COO− (aq), are oxidized to carbon dioxide gas.

[Source: Belafi-Bako, K., Vajda, B., Bakonyi, P., Nemestothy, N., 2014.
emoval of COD by Two-Chamber Microbial Fuel
Cells. The scheme of a two-chamber microbial fuel cell [image online].
Available at: https://www.intechopen.com/books/technology-
and-application-of-microbial-fuel-cells/removal-of-cod-by-two-chamber-microbial-fuel-cells
[Accessed 20 May 2021]. Source adapted.]

(d.i)

Outline the function of the proton exchange membrane.

[1]

Markscheme

allow H+ ions to pass through/diffuse/move «from anode to cathode» ✓

 

Do not accept diffusion of electrons or small molecules.

(d.ii)

Write equations for the reactions occurring at the anode and cathode, and an overall equation for a microbial fuel cell containing ethanoate ions.

 

Anode:

 

 


Cathode:

 


Overall equation:

 

 

 

[1]

Markscheme

Anode: CH3COO−(aq) + 2H2O(l) → 2CO2(g) + 7H+(aq) + 8e− ✓

Cathode: O2(g) + 4H+(aq) + 4e− → 2H2O(l) ✓

Overall Equation: CH3COO−(aq) + H+(aq) + 2O2(g) → 2CO2(g) + 2H2O(l) ✓

(d.iii)

Suggest one reason why microbial fuel cells might be a sustainable energy source.

[3]

Markscheme

fuel supply is wastewater/organic material ✓

 

Accept bacterium reproduces.