Question

Given
\(\mathrm{Co^{3+} + e^- \to Co^{2+}}\) ; \(\mathrm{E^o}\) = + 1.81 V
\(\mathrm{Pb^{4+} + 2e^- \to Pb^{2+}}\) ; \(\mathrm{E^o}\) = + 1.67 V
\(\mathrm{Ce^{4+} + e^- \to Ce^{3+}}\) ; \(\mathrm{E^o}\) = + 1.61 V
\(\mathrm{Bi^{3+} + 3e^- \to Bi}\) ; \(\mathrm{E^o}\) = + 0.20 V
Oxidizing power of the species will increase in the order :

• A. \(\mathrm{Co^{3+} \lt Ce^{4+} \lt Bi^{3+} \lt Pb^{4+}}\)
• B. \(\mathrm{Co^{3+} \lt Pb^{4+} \lt Ce^{4+} \lt Bi^{3+}}\)
• C. \(\mathrm{Ce^{4+} \lt Pb^{4+} \lt Bi^{3+} \lt Co^{3+}}\)
• D. \(\mathrm{Bi^{3+} \lt Ce^{4+} \lt Pb^{4+} \lt Co^{3+}}\)

Hint:

Oxidising power increases with the standard reduction potential.

Answer 1

The Correct Option is D

A species with a higher standard reduction potential is more easily reduced, i.e. a stronger oxidising agent.
Reduction potentials: \(\mathrm{Co^{3+}}\) = +1.81 V, \(\mathrm{Pb^{4+}}\) = +1.67 V, \(\mathrm{Ce^{4+}}\) = +1.61 V, \(\mathrm{Bi^{3+}}\) = +0.20 V.
Increasing oxidising power (increasing \(\mathrm{E^o}\)): \(\mathrm{Bi^{3+}}\) (0.20) < \(\mathrm{Ce^{4+}}\) (1.61) < \(\mathrm{Pb^{4+}}\) (1.67) < \(\mathrm{Co^{3+}}\) (1.81).
Answer: (4) \(\mathrm{Bi^{3+} \lt Ce^{4+} \lt Pb^{4+} \lt Co^{3+}}\)