Question

Find Empirical & Molecular Formula

Answer 1

Let the total mass be 100 g. Out of this composition 76.6 g is Carbon, 6.38 g is Hydrogen, Rest is oxygen

Oxygen = 100 g - ( 76.6 g + 6.38 g )

Oxygen = 100 g - 82.98 = 17.02 g

So now number of moles must be calculated.

Number of moles = Given Mass / Molar mass

Carbon = 76.6 / 12 = 6.38 moles

Hydrogen = 6.38 / 1 = 6.38 moles

Oxygen = 17.02 / 16 = 1.06 moles

So we get the ratio as follows:

Carbon = 6.38 / 1.06 = 6.01 which is approximately 6

Hydrogen = 6.38 / 1.06 = 6.01 which is approximately 6

Oxygen = 1.06 / 1.06 = 1

So Empirical formula = C₆H₆O

Empirical Mass = 12 * 6 + 1 * 6 + 16 = 72 + 6 + 16 = 94 g

Molecular Mass = 2 * Vapour Density

Molecular Mass = 2 * 47 = 94 g

Hence Molecular Mass and the Empirical Mass both are 94 g.