Question

# (a) What type of a battery is lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.(b) Calculate the potential for half-cell containing 0.10 M K2Cr2O7 (aq), 0.20 M Cr3+(aq) and 1.0 x 10-4 M H+ (aq)The half-cell reaction is And the standard electrode potential is given as E0 = 1.33 V. OR(a) How many moles of mercury will be produced by electrolysing 1.0 M?Hg (NO3)2 solution with a current of 2.00 A for 3 hours?[Hg (NO3)2 = 200.6 g mol-1](b) A voltaic cell is set up at 25°C with the following half-cells Al3+ (0.001 M) and Ni2+ (0.50 M). Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.

(a) A lead storage battery is a secondary battery.

The following chemical equations take place in a lead storage battery.

When a battery is charged, the reverse of all these reactions takes place.

Hence, on charging, PbSO4(s) present at the anode and cathode is converted into Pb(s) and PbO2(s) respectively.
b)
Or

(a) Quantity of electricity passed = (2A) x (3 x 60 x 60s) = 21600 C

Thus, 2F i.e. 2 x 96500 C deposit Hg = 1 mole 21600 C will deposit Hg

= 0.11 mole
Or

At anode:             Al (s)                  -->     Al3+ (aq) + 3e-] x2

At cathode:          Ni2+ + 2e-               -->   Ni(s)                ] x3

Cell reaction:     2Al(s) + 3Ni2+(aq) --->   2Al3+(aq)  + 3Ni (s)

Applying nernst equation to the above cell reaction