Question

Aluminium displaces hydrogen from acids, but copper does not. A galvanic cell prepared by combining $Cu/ Cu^{2+}$ and $Al/Al^{3+}$ has an emf of 2.0 V at 298 K. If the potential of copper electrode is +0.34 V, that of Aluminium electrode is

• A. -2.3 V
• B. +2.34 V
• C. -1.66 V
• D. 1.66 V

Answer 1

Answer: (C)

The given statement explains that Al is placed above Cu in E.C.S. hence it can reduce Cu from its salt solution (reduction). Thus Al acts as a reducing agent
now, Given : electrode potential of copper
$\left( E ^{\circ}_{cell}\right)=+0.34\, V$
e.m.f of cell = $2\, V$
We know that,
emf of a galvanic cell ( $E _{\text {cell }}^{\circ}$ ) = electrode potential of Cu (cathode) - electrode potential of Al (anode)
$2.0=0.34- E ^{\circ} Al$
$E ^{\circ} Al =0.34-2.00=-1.66\, V$