Question

A- flask contains 3.2 g of sulphur dioxide. Calculate the following (i) the moles of sulphur dioxide present in the flash (ii) the number of molecules of sulphur dioxide present in the flask.

Answer 1

Step 1. 3.2 g of sulphur dioxide (${\mathrm{SO}}_2$)

Step 2. No. of moles $=\frac{\mathrm{Mass}\mathrm{of}\mathrm{compound}}{\mathrm{Molecular}\mathrm{weight}}$

and no. of molecules $=\mathrm{moles}\times 6.02\times {10}^{23}$

Step 3. (i) No. of moles $=\frac{3.2\mathrm{g}}{64}$

$=0.05$

(ii) No. of molecules $=0.05\times 6.02\times {10}^{23}$

$=3.01\times {10}^{22}\mathrm{molecules}$

Therefore, moles of sulphur dioxide is 0.05 moles and number of molecules is $\mathbf{3}\mathbf{.}\mathbf{01}\mathbf{\times }{\mathbf{10}}^{\mathbf{22}}\mathbf{molecules}\mathbf{}$