Question

What is the ratio of empirical formula mass to molecular formula mass of benzene?
(A) $ 1:6 $
(B) $ 2:3 $
(C) $ 6:1 $
(D) $ 3:2 $

Answer 1

Hint: The molecular formula is the representation of the atoms in the compound. The empirical formula is the shortest or simplest representation of all the atoms in the compound in a simple ratio. Benzene is an aromatic compound with the molecular formula of $ {C_6}{H_6} $ , and the empirical molecular formula is $ CH $ .

Complete answer:
Benzene is an aromatic compound with the molecular formula of $ {C_6}{H_6} $ . It is an aromatic compound as it is cyclic, planar, all the carbon atoms in benzene are $ s{p^2} $ hybridisation, the electrons are involved in conjugation, and the pi-electrons are equal to $ 6 $ , which satisfies the condition of $ \left( {4n + 2} \right)\pi $ electrons i.e.. huckel’s rule.
The molecular formula of a benzene is $ {C_6}{H_6} $ . Thus, the molar mass of benzene will be
 $ 6\left( {12} \right) + 6\left( 1 \right) = 78 $
The empirical formula is the simplest ratio of molecular formula, The empirical formula will be $ CH $ .
Thus, the empirical mass will be $ 6 + 1 = 7 $
The obtained molar mass has $ 78 $ and the empirical mass is $ 7 $
The ratio of empirical formula mass to molecular formula mass will be $ 7:78 $
By simplification, the ratio will be $ 1:6 $
Thus, option $ A$ is the correct one.

Note:
Empirical formula is the shortest or simplest formula of molecular mass. For some chemical compounds, both the empirical formula and molecular formula were the same. The least simple ratio must be considered while writing the empirical formula of the chemical compound.