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?

1 Answer
Jun 28, 2018

molecular formula for
benzene = #C_6H_6#
acetylene = #C_2H_2#


Since the question already gave the empirical formula for both compounds, which is CH. Let's figure out the subscript, n, in #(CH)_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:
#"subscript, n" = "molar mass benzene"/"formula mass of CH"="78 g"/"13 g"=6#

molecular formula for benzene = #(CH)_6=C_6H_6#

For acetylene:
#"subscript, n" = "molar mass acetylene"/"formula mass of CH"="26 g"/"13 g"=2#

molecular formula for acetylene = #(CH)_2=C_2H_2#