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Question

In order to determine the identity of a particular lanthanide metal (M), a voltaic cell is constructed at 25ºC with the anode consisting of the lanthanide metal as the electrode immersed in a solution of 0.0873 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 2.68 V. What is the identity of the metal?

Reduction Half-ReactionEº(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

A) Sm
B) Gd
C) Tm
D) Eu
E) Ce

Answer

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