Question

When electric current is passed through acidified water for $1930\, s , 1120 \,mL$ of $H _{2}$ gas is collected (at STP) at the cathode. What is the current passed in amperes?

• A. 0.05
• B. 0.50
• C. 5.0
• D. 50

Answer 1

Answer: (C)

Electrolysis of water takes place as follows
$H _{2} O \rightleftharpoons\underset{\text { cathode }}{ H ^{+}}+\underset{\text { anode }} OH ^{-}$
At anode
$OH ^{-} \xrightarrow{\text { Oxidation }}OH +e^{-} $
$4 OH \longrightarrow 2 H _{2} O + O _{2}$
At cathode
$2 H ^{+}+2 e^{-} \xrightarrow{\text { Reduction }}H _{2}$
Given, time, $\quad t=1930\, s$
Number of moles of hydrogen collected
$=\frac{1120 \times 10^{-3}}{22.4}$ moles $=0.05$ moles
$\because 1$ mole of hydrogen is deposited by $=2$ moles of electrons
$\therefore 0.05$ moles of hydrogen will be deposited by
$=2 \times 0.05$
$=0.10$ mole of electrons
Charge, $Q=n F$
$=0.1 \times 96500$ Charge, $Q=i t$
$0.1 \times 96500 =i \times 1930 $ $i =\frac{0.1 \times 96500}{1930} $
$=5.0 \,A$