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Q.
Normal aluminium electrode coupled with normal hydrogen electrode gives an emf of 1.66 V. So the standard electrode potential of aluminium is,
Electrochemistry
Solution:
$Al$ is above hydrogen in the electrochemical series, therefore $Al^{3+}$ has lesser reduction tendency as compared with $H^{+}$ Hence, hydrogen electrode acts as anode when coupled with aluminium electrode.
$E^{\circ}_{cell}=E^{\circ}_{H^{+}H_{2}} -E^{\circ}_{Al^{3+}Al} $
$\therefore 1.66V =0.0V -E^{\circ}_{Al^{3+}Al}$
$E^{\circ}_{Al^{3+} Al}=-1.66 V.$