Question

Calculate the number of molecules in 12.8 g of sulphur dioxide gas. Take Avogadro's number as 6 × 10²³.
[S = 32, O = 16]

Answer 1

Molecular mass of sulphur dioxide (SO₂) gas = [32 + (2$\times$16)] g mol⁻¹ = 64 g mol⁻¹

Number of molecules of sulphur dioxide in 64 g = 6 × 10²³
Number of molecules of sulphur dioxide in 12.8 g = $\frac{12.8}{64}\times 6\times {10}^{23}=1.2\times {10}^{23}$
Hence, there are 1.2 × 10²³ molecules in 12.8 g of sulphur dioxide​ gas.