A compound is combusted that contains only carbon and hydrogen, and it is found to be 85.6% C by mass. What is the compound's empirical formula?

Answer 1

The empirical formula is the simplest positive integer ratio of atoms present in a compound, i.e. simplest whole number subscripts.

Since this compound has only C and H, and C is 85.6%, then H must be 100% - 85.6% = 14.4%

We can convert these % to grams if we assume we have 100 g of material. And then convert to moles.

85.6 g C x 1 mol C/12 g = 7.13 moles C

14.4 g H x 1 mol H/1 g = 14.4 moles H

Divide both by 7.13 to get whole numbers and we have...

C = 7.13/7.13 = 1 mol C

H = 14.4/7.13 = 2.0 mol H

Empirical formula = CH₂