Question

An elemental analysis of the acid indicates that it is composed of 5.89% H , 70.6% C , and 23.5% O by mass. What is its molecular formula?

Answer 1

Answer:

Empirical formula of acid is = C₄H₄O

In order to find the molecular formula we must have molar mass of compound. Because,

Molecular formula = n × (empirical formula)

 n = molar mass of compound / empirical formula mass

Explanation:

No. of gram atoms of carbon = 70.6 g /12 g/mol = 5.88 g atom

No. of gram atoms of hydrogen =5.89 g / 1.008 g/mol = 5.84 g atom

No. of gram atoms of oxygen = 23.5 g / 16 g/mol = 1.47 g atom

Atomic ratio:

   C :H :O               5.88/ 1.47    :   5.84/ 1.47   :  1.47 /1.47

   C :H :O                4 : 4 : 1

empirical formula of acid is = C₄H₄O

Molecular formula:

  Molecular formula = n × (empirical formula)

  n = molar mass of compound / empirical formula mass

  empirical formula mass= 4 × 12 + 4 × 1.008  + 1 × 16

   empirical formula mass= 48+ 4.032 +16 = 68.032