Question

Potentiometry is to be used to determine the concentration of a metal dication, M2+,
in water. The table below shows the dependence of the cell potential on [M2+]
(please note some data has been deliberately omitted).

[M2+] / mol l-1	ECell / V
1
0.5	-0.295
0.1	-0.309
0.05	-0.325
0.025
0.01	-0.349
0.005	-0.354

Q 2(a)
With the aid of a graph, determine the Nernst slope and the Standard Cell Potential,
Eo’. Comment on the values obtained and state the number of electrons transferred.

Q 2(b)
Clearly explaining your reasoning, use the graph to estimate the potentials that are
missing in the table. Comment on the likely accuracy of your predictions.

Q 2(c)
The Standard Cell Potential for Cd2+/Cd is -0.43V, for Pb2+/Pb is -0.29 V and for
Cu2+/Cu is +0.34 V. Clearly explaining your reasoning, determine the likely identity
of the metal cation.

Q 2(d)
If the potential measured for an unknown solution is -0.318 V, determine the
concentration of M2+ in the sample.

Answer 1

The plot between In(1/M2+) VS Ecell

Ans2d