A-LevelChemistryElectrochemistry9701/42 · Oct/Nov 2017 · Q49 Marks
An electrochemical cell consists of a half-cell containing V³+(aq) and V²+(aq) ions and another half-cell containing VO2+(aq) and VO2+(aq) ions.
- (a)(i)Use data from the Data Booklet to calculate a value for the E°cell.[1]
- (a)(ii)Write the ionic equation for the cell reaction.[1]
- (a)(iii)Draw a fully labelled diagram of the apparatus you could use to measure the potential of this cell. Include the necessary chemicals.[4]
- (b)(i)• V²⁺(aq) and Sn⁴⁺(aq) Does a reaction occur? equation E°cell[3]
- (b)(ii)• VO2+(aq) and Fe3+(aq) Does a reaction occur? equation E°cell[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [1] E°cell = 1.00 – (–0.26) = (+)1.26 V
- [1] VO₂⁺(aq) + V²⁺(aq) + 2H⁺(aq) → VO²⁺(aq) + V³⁺(aq) + H₂O(l)
- [1] solutions labelled correctly in one half-cell [1]
- [1] solutions labelled correctly in both half-cells [1]
- [1] two graphite or platinum electrodes [1]
- [1] salt bridge and voltmeter [1]
- [1] yes and Ecell = +0.15 − (−0.26) = +0.41 V [1]
- [1] 2V²⁺ + Sn⁴⁺ → 2V³⁺ + Sn²⁺ [1]
- [1] VO²⁺(aq) and Fe³⁺(aq)
- [1] no reaction [1]
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