Assuming a basis of 100 g of Kevlar, therefore the masses are:
C = 70.6 g
H = 4.2 g
N = 11.8 g
O = 13.4 g
We know the molar masses are:
C = 12.01, H = 1.008, N = 14.01, O = 16.00
Calculating for the moles per element:
C = 70.6 / 12.01 = 5.88 mol
H = 4.2 / 1.008 = 4.17 mol
N = 11.8 / 14.01 = 0.84 mol
O = 13.4 / 16 = 0.84 mol
To get the empirical formula, the next step is to divide everything by the smallest moles = 0.84. So:
C = 7
H = 5
N = 1
O = 1
Hence the empirical formula is:
C7H5NO
