Question

A carbohydrate P contains 40% carbon,6.67% hydrogen.If P has a relative molecular mass of 60.Determine it; 1)Empirical formula 2)molecular formula [H=1,C=12,O=16]

Answer 1

Take a 100 g sample which gives you
50 g C
6.67 g H
100-6.67-40 = 53.33 g O

mols C = 40/12 = 3.33
mols H = 6.67/1 = 6.67
mols O = 53.33/16 = 3.33

Find the ratio to each other with the smallest being no less than 1.00. The easy way to do that is to divide all of the numbers by the smallest.
3.33/3.33 = 1 = C
6.67/3.33 = 2 = H
3.33/3.33 = 1 = O
Empirical formula = CH2O
Empirical mass = 12 + 2 + 16 = 30

So molecular formula must be 60/30 = 2 or (CH2O)2 = C2H4O2