Question

Silicon forms a compound with chlorine in which 5.6 g of silicon is combined with 21.3 g of chlorine. Calculate the formula of the compound (Atomic mass :Si =28 : Cl =35.5).

Answer 1

Given,

Mass of $\mathrm{Si}$= 5.6 g

Mass of $\mathrm{Cl}$= 21.3 g

We know that,

Moles of $\mathrm{Si}$= 5.6 g ($\frac{1\mathrm{mol}}{28.08\mathrm{g}}=0.199\mathrm{moles}\mathrm{of}\mathrm{Si}$)

Moles of $\mathrm{Cl}$= 21.3 g ($\frac{1\mathrm{mol}}{35.45\mathrm{g}}=0.601\mathrm{moles}\mathrm{of}\mathrm{Cl}$)

Now we calculate the mole ratio of $\mathrm{Si}$ and $\mathrm{Cl}$ and for this we divide the moles of each by the least one of them. Here the least one is $\mathrm{Si}$ as we have less moles in it.

$$\begin{gathered} \mathrm{Si}=\frac{0.199}{0.199}=1 \\ \mathrm{Cl}=\frac{0.601}{0.199}=3 \end{gathered}$$

So the empirical formula is ${\mathrm{SiCl}}_3$