Question

A flask contains 3.2 g of sulphur dioxide. Calculate the following :

(a) The moles of sulphur dioxide present in the flask.

(b) The number of molecules of sulphur dioxide present in the flask.

(c) The volume occupied by 3.2 g sulphur dioxide at S.T.P.

Answer 1

(a) 1 mole of sulphur dioxide ${\mathrm{SO}}_2$= Molecular mass of ${\mathrm{SO}}_2$

Molecular mass of ${\mathrm{SO}}_2$= Mass of $\mathrm{S}+2\times$Mass of $\mathrm{O}$

$$\begin{gathered} =32+\hspace{0.17em}2\times 16 \\ =64g \end{gathered}$$

64 g of ${\mathrm{SO}}_2$= 1 mole of ${\mathrm{SO}}_2$

3.2 g of ${\mathrm{SO}}_2$= $\frac{1}{64}\times 3.2$= 0.05 moles.

(b) 1 mole of sulphur dioxide ${\mathrm{SO}}_2$= Avogadro's number of molecules

1 mole of ${\mathrm{SO}}_2$= $6.023\times {10}^{23}$

0.05 moles of ${\mathrm{SO}}_2$ $$\begin{gathered} =6.023\times {10}^{23}\times 0.05 \\ =3.0\times {10}^{22} \end{gathered}$$

(c) The volume occupied by 64g of ${\mathrm{SO}}_2$ $=22.4$dm³

3.2 g of ${\mathrm{SO}}_2$ will be occupied by volume $=22.4\times \frac{3.2}{64}$

3.2 g of ${\mathrm{SO}}_2$ will be occupied by volume = 1.12 dm³