Question

What is the empirical formula for a sample containing 81.70% carbon and 18.29% hydrogen?

Answer 1

Given:  C= 81.70% = 81.70g 
            H = 18.29% = 18.29g 

The number of moles is given by: n= Given mass (m)/Molar Mass (M)
M of C = 12 g/mol
M of H = 1 g/mol
Thus, the number of moles of carbon = 81.70g / 12gmol= 6.83moles 
and, the number of moles of hydrogen = 18.29/1g/mol = 18.29 moles
The ration of C moles with hydrogen : 
H:C = 18.29moles/6.83moles= 2.67 ≈3

Thus, the empirical formula is C3H8