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Date May 2021 Marks available 1 Reference code 21M.2.hl.TZ2.3
Level HL Paper 2 Time zone TZ2
Command term Calculate Question number 3 Adapted from N/A

Question

Oxidation and reduction reactions can have a variety of commercial uses.

A student decides to build a voltaic cell consisting of an aluminium electrode, Al (s), a tin electrode, Sn (s), and solutions of aluminium nitrate, Al(NO3)3 (aq) and tin(II) nitrate, Sn(NO3)2 (aq).

Electron flow is represented on the diagram.

Label each line in the diagram using section 25 of the data booklet.

[3]
a.

Write the equation for the expected overall chemical reaction in (a).

[1]
b.

Calculate the cell potential using section 24 of the data booklet.

[1]
c.

Calculate the Gibbs free energy change, ΔG, in kJ, for the cell, using section 1 of the data booklet.

[2]
d.

Markscheme

Al/aluminium «electrode» AND aluminium nitrate/Al(NO3)3/Al3+ on left ✓

Sn/tin «electrode» AND tin«(II)» nitrate/Sn(NO3)2/Sn2+ on right ✓

salt bridge AND voltmeter/V/lightbulb ✓


Award [1] if M1 and M2 are reversed.

Award [1] for two correctly labelled solutions OR two correctly labelled electrodes for M1 and M2.

Accept a specific salt for “salt bridge”.

Accept other circuit components such as ammeter/A, fan, buzzer, resistor/heating element/R/Ω.

a.

3Sn2+ (aq) + 2Al (s) → 3Sn (s) + 2Al3+ (aq)
OR
3Sn(NO3)2 (aq) + 2Al (s) → 3Sn (s) + 2Al(NO3)3 (aq) ✓

If half cells are reversed in part-question (a) then the equation must be reversed to award the mark.

Do not penalize equilibrium arrows.

b.

«1.66 + (−0.14) = +»1.52 «V» ✓

 

Calculation must be consistent with equation given in 3 b.

c.

«ΔG = −nFE = −6 × 9.65 × 104 × 1.52 =» −880080 «J mol−1»
OR
6 «electrons» ✓

«-8800801000=» −880 «kJ» ✓

 

Award [1] for “«+»880”.

Award [2] for correct final answer.

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.

Syllabus sections

Additional higher level (AHL) » Topic 19: Redox processes » 19.1 Electrochemical cells
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Additional higher level (AHL) » Topic 19: Redox processes
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