Calculate the empirical formulas of the following polymer: Saran; 30.1% C, 3.2% H, 66.7% Cl

Answer 1

To find the empirical formula, we want to find the number of moles of each element, and then report them as whole numbers.

If we assume we have 100 g of the polymer, then % becomes grams.

30.1 g C x 1 mol C/12.01 g = 2.506 moles C

3.2 g H x 1 mol H/1.01 g = 3.168 moles H

66.7 g Cl x 1 mol Cl/35.45 g = 1.88 moles Cl

We can divide all by 1.88 to try to get whole numbers of moles:

2.506/1.88 = 1.33 mol C

3.168/1.88 = 1.69 mol H

1.88/1.88 = 1.0 mol Cl

Still not whole numbers, so let us multiply all by 3 to obtain...

1.33 x 3 = 3.99 mol C = 4 moles C

1.69 x 3 = 5.07 mol H = 5 moles H

1.0 x 3 = 3.0 moles Cl

Empirical formula = C₄H₅Cl₃