Question

A galvanic cell is set up from a zinc bar weighing 100 g and 1.0 litre of 1.0 M Cu $SO_4$ solution. How long would the cell run if it is assumed to deliver a steady current of 1.0 ampere ? (Atomic mass of Zn = 65)

• A. 1.1 hr
• B. 46 hr
• C. 53.6 hr
• D. 24.00 hr

Answer 1

Answer: (C)

53.6 hr

Answer 2

$100 \,g$ of $Zn = \frac{100}{65}$ mol. Thus, according to reaction, $Zn + Cu^{2+} {->} Zn^{2+} + Cu, Cu^{2+}$ ions are limiting reagents. Now, charge flowing for reduction of $1$ mole of $Cu^{2+}$ ions $= 2 \times 96500 \,C$ If $1$ ampere of current is to be delivered for $t$ hours, the quantity of electricity is $3600\,t\,C$. Now $3600\,t = 2 \times 96500$ $t = \frac{2\times 96500}{3600} = 53.61\,hr$