Question

The standard reduction potentials of Ag, Cu, Co and Zn are 0.799, 0.337, -0.277 and -0.762 V respectively. Which of the following cells will have maximum e. m. f?

• A. $\text{Zn }|\text{ Z}{\text{n}}^{2+}\text{(1M) }||\text{ C}{\text{u}}^{2+}(1M)|Cu$
• B. $\text{Zn }|\text{ Z}{\text{n}}^{2+}\text{(1M) }||\text{ A}{\text{g}}^{+}(1M)|Ag$
• C. $\text{Cu }|\text{ C}{\text{u}}^{2+}\text{(1M) }||\text{ A}{\text{g}}^{+}(1M)|Ag$
• D. $Zn|Z{n}^{2+}(1M)||C{o}^{2+}(1M)|Co$

Answer 1

Answer: (B)

Standard reduction potentials of Ag = 0.799V Cu = 0.337V Co = - 0.277V Zn = -0.762V Maximum value of emf is possible when extreme +ve value of standard reduction potential connected with the extreme $-\text{ve}$ value of standard reduction potential to form a cell. In the above data Ag has extreme $\text{+}\text{ve}$ value and Zn has extreme $-\text{ve}$ value. Hence, cell formed by silver and zinc electrode have maximum value of e. m. f.