224 cm³ of ammonia undergoes catalytic oxidation in presence of Pt to given nitric oxide and water vapour. Calculate the volume of oxygen required for the reaction. All volumes measured at room temperature and pressure.

[By Lussac's law]

$\begin{matrix} 4\text{NH}$3 & + & 5\text{O}2 & \longrightarrow & 4\text{NO} & + & 6\text{H}_2\text{O} \ 4 \text{ vol.} & : & 5 \text{ vol.} & \longrightarrow & 4\text{ vol.} & : & 6\text{ vol.} \end{matrix}

To calculate the volume of oxygen required.

$\begin{matrix} \text{NH}$3 & : & \text{O}2 & \ 4 & : & 5 \ 224 & : & x \end{matrix}

Therefore,

$\dfrac{5}{4} \times 224 = x \\[0.5em] \Rightarrow x = 280 \text{ cm}^3$

Therefore, volume of oxygen required is 280 cm³.