Ammonia gas, NH₃, is formed by reacting ammonium chloride, NH₄Cl, with sodium hydroxide, NaOH - Edexcel - GCSE Chemistry - Question 3 - 2016 - Paper 1

Using the mass of sodium hydroxide provided:

$\text{Moles of NaOH} = \frac{\text{Mass}}{\text{Molar Mass}} = \frac{4.0 \text{ g}}{40 \text{ g/mol}} = 0.1 \text{ moles}$

From the balanced chemical equation, the molar ratio of NaOH to NH₃ is 1:1. Thus, moles of ammonia produced will also be 0.1 moles.

Using the molar volume at room temperature and pressure (24 dm³ per mole):

$\text{Volume of ammonia} = \text{Moles} \times 24 \text{ dm³/mol} = 0.1 \text{ moles} \times 24 \text{ dm³/mol} = 2.4 \text{ dm³}$