In order to determine the identity of a particular lanthanide metal (M), a voltaic cell is constructed at 25°C with the anode consisting of the lanthanide metal as the electrode immersed in a solution of 0.0467 M MCl3, and the cathode consisting of a copper electrode immersed in a 1.00 M Cu(NO3)2 solution. The two half-reactions are as follows:

M(s)  M3+(aq) + 3e–

Cu2+(aq) + 2e– Cu(s)

The potential measured across the cell is 2.70 V. What is the identity of the metal?

Reduction Half-Reaction

E° (V)

Cu2+(aq) + 2e– Cu(s)

0.34

Ce3+(aq) + 3e– Ce(s)

–2.336

Tm3+(aq) + 3e– Tm(s)

–2.319

Eu3+(aq) + 3e– Eu(s)

–1.991

Gd3+(aq) + 3e– Gd(s)

–2.279

Sm3+(aq) + 3e– Sm(s)

–2.304

Tm

Gd

Ce

Eu

Sm