Question

A sample of aspirin (acetyl salicyclic acid) of molecular mass 180, on analysis was found to contain 60% carbon, 4.4% hydrogen and 35.6% oxygen

i.Determine the empirical formula of aspirin

ii. What is the molecular formula of aspirin?

iii. State the technique that can be used to determine the molecular weight of aspirin

Answer 1

% of Carbon = 60 % .

% of hydrogen = 4.4 % .

% of Oxygen = 35.6 % .

Moles of carbon = 60 / 12 = 5 mol .

Moles of hydrogen = 4.4 / 1 = 4.4 mol.

Moles of oxygen = 35.6 / 16 = 2.225 mol.

When we devide each by 2.2 and multiply by 4

Moles of C = 5 / 2.2 = 2.25 × 4 = 9

Moles of hydrogen = 4.4 / 2.2 = 2 ×4 = 8

Moles 0f Oxygen = 2.2 / 2.2 =1 × 4 = 4

Emperical Formula = C₉H₈O₄.

Emperical mass = 9 ×12 + 1×8 + 4×16 = 180 .

n = Molecular mass / Emperical mass .

n = 180 / 180 = 1 .

Molecular Formula = C₉H₈O₄.