How is the percentage of sulphur determined in a solid fuel?

Principle: the sulphur in the solid fuel is converted to sulphate, precipitated as BaSO₄ and weighed.

1. A known mass (W g) of the fuel is burnt completely in oxygen in a bomb calorimeter. S is oxidised to SO₂/SO₃, which dissolves in the water in the bomb as sulphuric acid: \( \mathrm{S + O_2 \rightarrow SO_2};\ \mathrm{2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4} \)
2. The bomb washings are collected, acidified with dilute HCl and boiled.
3. Excess BaCl₂ solution is added: \( \mathrm{H_2SO_4 + BaCl_2 \rightarrow BaSO_4\downarrow + 2HCl} \)
4. The BaSO₄ precipitate is filtered, washed, dried, ignited and weighed.

Calculation: 233 g of BaSO₄ contains 32 g of S, so

\( \%S = \dfrac{\text{wt. of BaSO}_4 \times 32 \times 100}{233 \times W} \)