Question

A 3.000 g sample of an organic compound was heated in oxygen and produced 7.568 g of CO₂ and 1.328 g of water.

a. Determine the empirical formula of the substance.







b. In a separate experiment, the molar mass of the compound was determined to be 122.1. What is the molecular formula of the compound?

Answer 1

Ans

a) Number of moles of C = number of moles of CO2 = 7.568 / 44.01 = 0.172 moles

Mass of carbon = 12.01 x 0.172 = 2.06 g

Number of moles of H2O = 1.328 / 18.01528 = 0.074 moles

So number of H atoms = 2 x 0.074 = 0.148 moles

Mass of H = 0.148 x 1.008 = 0.149 grams

Mass of Oxygen = 3.000 - 2.06 - 0.149 = 0.791 g

Number of moles of O = 0.791 / 15.999 = 0.049 moles

Dividing the number of moles by a common value to get the ratio as : 7 : 6 : 2

SO the empirical formula of the compound becomes : C₇H₆O₂

B) the empirical mass = 7 (12.01) + 6(1.008) + 2(15.999) = 122.117 g/mol

DIviding molar mass / empirical mass = 122.1 / 122.117

=1

Multipying this value to the empirical formula

We get the molecular formula as C₇H₆O₂