# Benzene and acetylene have the same empirical formula, CH. However, benzene has a molar mass of 78 g, and acetylene has a molar mass of 26 g, what are the molecular formulas of benzene and acetylene?

Jun 28, 2018

molecular formula for
benzene = ${C}_{6} {H}_{6}$
acetylene = ${C}_{2} {H}_{2}$

#### Explanation:

Since the question already gave the empirical formula for both compounds, which is CH. Let's figure out the subscript, n, in ${\left(C H\right)}_{n}$ for their molecular formulas.

To do so, let's use the molar mass and divide by the formula mass of the empirical formula, CH, 12 + 1 = 13 g.

For benzene:
$\text{subscript, n" = "molar mass benzene"/"formula mass of CH"="78 g"/"13 g} = 6$

molecular formula for benzene = ${\left(C H\right)}_{6} = {C}_{6} {H}_{6}$

For acetylene:
$\text{subscript, n" = "molar mass acetylene"/"formula mass of CH"="26 g"/"13 g} = 2$

molecular formula for acetylene = ${\left(C H\right)}_{2} = {C}_{2} {H}_{2}$