A sample of trifluoroacetic acid, C2HF3O2, contains 38.9 g of oxygen. Calculate the mass of the trifluoroacetic acid sample.

138.6 g of  C₂HF₃O₂ have 38.9 g of O

Explanation:

Trifluoroacetic acid → C₂HF₃O₂

Molar mass = Mass of C . 2 + Mass of H + Mass of F . 3 + Mass of O .2

Molar mass = 12 . 2 + 1 . 1 + 19 . 3 + 16 . 2 = 114 g /mol

1 mol of C₂HF₃O₂ has:

2 moles of C

1 mol of H

3 moles of F

2 moles of O

If we state the relation in mass by g we say:

114 g of  C₂HF₃O₂ have 24g of C, 1 g of H, 57 g of F and 32 g of O

Let's make a rule of three:

32 g of O are contained in 114 g of  C₂HF₃O₂

38.9 g of O may be contained in (38.9 . 114) / 32 = 138.6 g