Molecular calculation / empirical formular

Question

Aspirin has the chemical formula C9H8O4.

1) How many grams of O are present in 1.25 moles of Aspirin?

1.25 = 15.999/1 = 19.999 = 20 gO

2) How many atoms of H are present in 1.25 moles of Aspirin?

1.25 x 1/8 H atom = = 0.1562 = 0.16 atom H

3) How many grams of Aspirin contains 16.8 grams of O?

16.8 x 1/20 = 0.84 gram

Is it correct or not? please check my answer.

Answer 1

Molar mass of C₉H₈O₄ = 180.16 g/mol. We will use dimensional analysis (unit factor method) to answer...

(1). 1.25 mol aspirin x 4 mol O/mol aspirin x 16 g O/mol O = 80 g O

(2). 1.25 mol aspirin x 6.02x10²³ molecules aspirin/mol x 8 H atoms/molecule = 6.02x10²⁴ H atoms

(3). % O in aspirin = 4 x 16/180 (x100%) = 35.6%

(0.356)(x) = 16.8 g

x = 47.2 g of aspirin needed