Question

A cell constructed by coupling a standard copper electrode and a standard magnesium electrode has emf of 2.7 volts. If the standard reduction potential of copper electrode is + 0.34 volt that of magnesium electrode is.

• A.
  • 3.04 volts
• B. – 3.04 volts
• C.
  • 2.36 volts
• D. – 2.36 volts

Answer 1

Answer: (D)

– 2.36 volts

Answer 2

Mg lies above Cu in electrochemical series and hence Cu electrode acts as cathode

$E_{cell}^{o} = E_{Cu^{+ +}/Cu}^{o} - E_{Mg^{+ +}/Mg}^{o}$ $2.70V = 0.34 - E_{Mg^{+ +}/Mg}^{o}$;

$E_{Mg^{+ +}/Mg}^{o} = - 2.36V$.