Question

Normal aluminium electrode coupled with normal hydrogen electrode gives an emf of 1.66 V. So the standard electrode potential of aluminium is,

• A. $-1.66V$
• B. $+1.66V$
• C. $-0.83V$
• D. $+0.83V$

Answer 1

Answer: (A)

$Al$ is above hydrogen in the electrochemical series, therefore $A{l}^{3+}$ has lesser reduction tendency as compared with $H^{+}$ Hence, hydrogen electrode acts as anode when coupled with aluminium electrode.
$E_{cell}^{\circ }=E_{H^{+}{H}_2}^{\circ }-E_{A{l}^{3+}Al}^{\circ }$
$\therefore 1.66V=0.0V-E_{A{l}^{3+}Al}^{\circ }$
$E_{A{l}^{3+}Al}^{\circ }=-1.66V.$