Question

In human medicine, hydroquinone is used as a skin whitening to reduce the color of skin. A sample of hydroquinone was found in the lab. Analysis of the powder determined it to be 65.4% C, 5.5% H and 29.1% O, by mass. What is the empeirical and molecular formula of hydroquinone? (hydroquinone has a molar mass of 110.11 g/mole)

Answer 1

Let the sample be 100 g

So the mass of C = 65.4 g

H = 5.5 g

O = 29.1 g

Number of moles of C = 65.4 / 12.01 = 5.44 moles

H = 5.5 / 1.008 = 5.46 moles

O = 29.1 / 15.999 = 1.82 moles

Dividing the number of moles by a common factor , we get the ratio as : 3:3:1

So the empirical formula of the compound becomes : C₃H₃O

The empirical mass = 3(12.01) + 3(1.008) + 15.999

= 55.053 g/mol

Dividing molar mass by empirical mass = 110.11 / 55.053 = 2

Multiplying this value with empirical formula , we get the molecular formula as :

C₆H₆O₂