Question

Calculate the volume of hydrogen gas that will be evolved at standard temperature and pressure when 12g of zinc are treated with excess dilute hydrochloric acid and the mass if zinc chloride formed.

Answer 1

The reaction between Zn and hydrochloric acid is next:

$$\mathrm{Zn} + 2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_2 + \mathrm{H}_2$$

One mole of gas occupies volume of 22.4 liters. From law: The molar volume of an ideal gas at standard temperature and pressure is 22.4 L.

Amount of Zn is next: n=m/Mr, where m is mass, Mr is molecular mass.

$$n = 12 / 65 = 0.185 \mathrm{mol}$$

The molar ratio of Zn : H₂ is 1: 1,

It means that amount of H₂ is 0.185 mol.

This amount occupies next volume:

$$V = 22.4 \mathrm{L/mol} \times 0.185 \mathrm{mol} = 4,144 \mathrm{L}$$