Percent Composition to Empirical Formula

Question

1) A compound is found to contain 45.71 % oxygen and 54.29 % fluorine by mass.

What is the empirical formula for this compound?

2) A compound is found to contain 7.962 % silicon, 20.10 % chlorine, and 71.94 % iodine by mass.

What is the empirical formula for this compound?

3) A compound is found to contain 14.87 % phosphorus and 85.13 % chlorine by mass.

What is the empirical formula for this compound?

Answer 1

When given % composition and asked for empirical/molecular formula, it's easiest to just go ahead and assume you 100 g of material. Then % is the same as grams.

I'll do (1), and you should be able to do the others.

45.71% O = 45.71 g O x 1 mol O/16 g = 2.86 moles O

54.29% F = 54.29 g F x 1 mol F/18.99 g = 2.86 moles F

Empirical formula = OF