Q. A cell constructed by coupling a standard copper electrode and a standard magnesium electrode has emf of 2.7 V. If the standard reduction potential of copper electrode is +0.34 V then that of the magnesium electrode is
A) $+ \ 2.36\ V$
B) $- \ 2.36\ V$
C) $+ \ 3.26\ V$
D) $- \ 3.26\ V$
Explanation
(b)
Mg lie above Cu in electrochemical series and hence, Cu electrode acts as cathode
$E_{cell}^{{^\circ}} = E_{{Cu}^{2 +}/\ Cu}^{{^\circ}} = E_{{Mg}^{2 +}/\ Mg}^{{^\circ}}$
$\therefore 2.70\ V = 0.34 - E_{{Mg}^{2 +}/Mg}^{{^\circ}}$
$\therefore E_{{Mg}^{2 +}/\ Mg}^{{^\circ}} = - 2.36\ V$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.