Question

Aluminum displace hydrogen from dilute $HCl$ whereas silver does not. The emf of a cell prepared by combining $Al/A{l}^{3+}$ and $Ag/A{g}^{+}$ is $2.46V$. The reduction potential of the silver electrode is $+0.80V$. The reduction potential of aluminum electrode is:

• A. $+1.66V$
• B. $-3.26V$
• C. $3.26V$
• D. $-1.66V$

Answer 1

The correct option is D $-1.66V$

Aluminium displace hydrogen from dilute $HCl$ whereas silver does not.
Hence, $Al$ has lower (negative) standard reduction potential than hydrogen whereas $Ag$ has a higher (positive) standard reduction potential than hydrogen. In the electrochemical series, $Al$ is below hydrogen and silver is above hydrogen.
The reduction potential of silver electrode is +0.80 V.
$E_{cell}^o=E_{Ag}^o-E_{Al}^o$
$2.46=0.80-E_{Al}^o$
$E_{Al}^o=-1.66V$
The reduction potential of aluminium electrode is $-1.66V$