Question

3.                  A naturally occurring acidic red pigment extracted from the cochineal insect contains only carbon, hydrogen and oxygen. It was commonly used as a dye in the first half of the nineteenth century. It is 53.66% C and 4.09% H by mass. Calculate the empirical formula for this dye.

Answer 1

Empirical formula stands for the least numebr of atoms present in the structure/compound

Let us assume a basis of 100 grams

Therefore:

53.66 g of C

4.09 g of H

and the rest must be O = 100 - (53.9+4.09) = 42.31 g

find molar masses

MW of C = 12 g/gmol

MW of H = 1 g/gmol

MW of O = 16 g/gmol

Convert all masses to moles

For carbon = 53.66/12= 4.47

For Hydrogen = 4.09/1= 4.09

For Oxygen = 42.31 / 16 = 2.64

Choose the smalles number, 2.64

divide all other

4.47/2.64 = 1.69

4.09/2.64 = 1.55

2.64/2.64 = 1.0

Nearest number might be:

C17H15O10

Or more precisely

C₁₆₉H₁₅₅O₁₀₀