Question

A gaseous compound has a composition by mass of 24.8% carbon, 2.08% hydrogen, and 73.1% chlorine. At STP, the gas has a density of 4.3 g/L. Draw a Lewis structure that satisfies these facts. Would another structure also satisfy them? Explain

Short answer

The required compound is ${\mathbf{C}}_1{\mathbf{H}}_1{\mathbf{Cl}}_1$

Step-by-step solution

Empirical formula  

Atom	Mass present in the compound	Moles present in the compound	Ratio
Hydrogen	2..08	$\frac{2.08}{1}=2.08$	$\frac{2.08}{2.06}=1$
Carbon	24.8	$\frac{24.8}{12}=2.06$	$\frac{2.06}{2.06}=1$
Chlorine	73.1	$\frac{73.1}{35.5}=2.06$	$\frac{2.06}{2.06}=1$

The empirical formula of the compound is ${\mathbf{C}}_1{\mathbf{H}}_1{\mathbf{Cl}}_1$.

Formula of the compound

The molar mass of the compound is calculated as below.

$\mathrm{M}=\frac{4.3\mathrm{g}/\mathrm{L}*0.0821\mathrm{L}\mathrm{atm}/\mathrm{molK}*273\mathrm{K}}{1\mathrm{atm}}$

Now.

$\mathrm{n}=\frac{\mathrm{molar}\mathrm{mass}}{\mathrm{empirical}\mathrm{mass}\mathrm{of}\mathrm{compound}}$

$\mathrm{n}=\frac{96.38}{48.5}=2$

Therefore, the possible formula of the compound is ${\mathbf{C}}_2{\mathbf{H}}_2{\mathbf{Cl}}_2$. This is dichloroethane.

Possible structures

Three possible structures are drawn. The three are isomers of each other.