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