Question

On electrolysis of a sample of acidified water, 22.4 ml of hydrogen was obtained. The volume of oxygen in ml obtained is:
A. 22.4
B. 44.8
C. 11.20
D. 2.24

Answer 1

Hint: we will write the balanced equation for electrolysis of water. The balanced equation will be used to determine the formed moles of oxygen and hydrogen. STP condition gives the relation between the number of moles and volume. By using STP conditions we can determine the volume of oxygen.

Complete step by step solution:
Hydrolysis of water gives hydrogen and oxygen. The equation of hydrolysis is as follows:
${\text{2}}\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to \,2\,{{\text{H}}_{\text{2}}}\,{\text{ + }}\,\,{{\text{O}}_{\text{2}}}$
So, according to the balanced equation, two moles of water give two moles of hydrogen and one mole of oxygen.
At standard temperature and pressure, one mole of gas occupies $22.4$ of volume.
By the electrolysis of a sample of acidified water, $22.4$ml of hydrogen was obtained means one-mole hydrogen was obtained.
With two-mole hydrogen one-mole oxygen was produces so, with one-mole hydrogen, the produced amount of oxygen is,
$2\,{\text{mol}}\,\,{{\text{H}}_{\text{2}}}\, = \,1{\text{mol}}\,\,{{\text{O}}_{\text{2}}}$
$1\,{\text{mol}}\,\,{{\text{H}}_{\text{2}}}\, = \,0.5\,{\text{mol}}\,\,{{\text{O}}_{\text{2}}}$
So, with one-mole hydrogen, the produced amount of oxygen is$0.5$mole.
Determine the volume of oxygen in ml obtained as follows:
One mole is equal to $22.4$L volume so, $0.5$ mole will be equal to,
One mole = $22.4$L
${\text{for half mole, volume = }}\,{\text{0}}{\text{.5}}\,{{ \times }}\,{\text{22}}{\text{.4}}\,{\text{ml}}$
${\text{for half mole,volume = 11}}{\text{.20}}\,\,{\text{ml}}$
So, the volume of oxygen in ml obtained is $11.20$ml.

Therefore, option (C) $11.20$ is correct.

Note: The STP is known as standard temperature and pressure. The value of standard temperature is $273\,{\text{K}}$. The value of the standard pressure is${\text{1}}\,{\text{atm}}$. One mole of a gas at $273\,{\text{K}}$ temperature and ${\text{1}}\,{\text{atm}}$ pressure occupies $22.4\,{\text{L}}$ volume. The ideal gas equation is as follows: $pV = nRT$. The STP temperature and pressure becomes constant. R is already constant, so the number of moles becomes a function of volume only. To compare the moles or volume, a balanced equation is necessary.