A-LevelChemistryElectrochemistry9701/42 · Feb/Mar 2018 · Q65 Marks

The apparatus shows a cell which can be used to determine a value of the Avogadro constant, L. [Figure with diagram of an electrolytic cell with silver electrodes, power supply, variable resistor, ammeter X, and electrolyte Y]

(a)(i)Name component X.[1]
(a)(ii)Suggest a suitable electrolyte Y.[1]
(b)In an experiment, a current of 0.200 A was passed through the cell for 40.0 minutes. The mass of the silver cathode increased by 0.500 g. The charge on the electron is −1.60 × 10⁻¹⁹ C. Calculate the: • number of moles of silver deposited on the cathode • number of coulombs of charge passed • number of electrons passed • number of electrons needed to deposit 1 mol of silver at the cathode.[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 (Feb/Mar 2018). The mark or mark type is shown in brackets.

[1] X is an ammeter
[1] Y is AgNO3 or AgF or AgClO4
[3] n(Ag) = 0.500 / 107.9 = 4.6(34) × 10⁻³ n(C) = 0.200 × 40 × 60 = 480 C n(e¯) = 480/1.60 × 10⁻¹⁹ = 3(.00) × 10²¹ n(e¯)/n(Ag) = 3.00 × 10²¹ / 4.634 × 10⁻³ = 6.474 × 10²³ (6.5 × 10²³)

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.