Question

Ethane and acetylene are two gaseous hydrocarbons. chemical analyses show that one sample of ethane contains 2.65 g of carbon and 0.668 g of hydrogen, and one sample of acetylene contains 4.56 g of carbon and 0.382 g of hydrogen. write reasonable empirical formulas for these compounds.

Answer 1

Ethane

C: 2.65 g

H: 0.668 g

1) Divide by the atomic mass of each element

C: 2.65 g / 12.0 g/mol = 0.2208 mol

H: 0.668 g / 1 g/mol = 0.668 mol

2) Divide by the smallest number of moles:

C: 0.2208 / 0.2208 = 1

H: 0.668 / 0.2208 = 3

=> Empirical formula CH3

Acetylene

C: 4.56 g

H: 0.382 g

1) Divide by the atomic mass

C: 4.56 g / 12.0 g/mol  = 0.38 mol

H: 0.382 g / 1 g/mol = 0.382 mol

2) Divide by the smallest number

C: 0.38 / 0.38 = 1

H: 0.382 / 0.38 = 1

=> Empirical formula: CH