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
Dr. K.
Jun 28, 2018

molecular formula for
benzene = C_6H_6
acetylene = C_2H_2

Explanation:

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

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