Account for the following:

(a) Rusting of iron is quicker in saline water than in ordinary water.

(b) Unlike dry cell, the mercury cell has a constant potential throughout its usual life.

OR

Define fuel cell. Write the electrode reaction in H₂ — O₂ fuel cell.

(a) Saline water contains many salts which increases the rate of electro chemical reactions and paces up the movement f electrons and hence increasing the rate of oxidation reactions. Rusting also occurs due to oxidation and hence it is rapid in saline water.

(b) The overall reaction of mercury cell is as follow:

ZnO+ Hg → HgO + Zn

The mercury cell has a constant potential throughout its life because no ions are involved in the overall reactions of mercury cells. When the ions are involved the electrolyte gets consumed slowly, and reduces the cell potential. But absence of ions makes the cell potential of mercury constant throughout its life.

OR

Fuels are those substances which have ability to give energy. Fuel cells are those electrochemical cells which can convert the chemical energy (produced from the chemical reaction of fuels) into electrical energy.

H₂-O₂ is highly effective and eco friendly fuel cells in which the energy released from the redox reactions of H₂-O₂. This method is highly efficient because it releases only water and energy and no other pollutant. And also its efficiency is very high. The reaction taking place in H₂O₂ fuel cell is a s follow:

H₂ + 1/2 O₂→ H₂O + energy