Question

Determine the empirical formula of kevlar, used in making bullet proof vests, is 70.6% c, 4.2% h, 11.8% n and 13.4% o.

Answer 1

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