Question

What is the empirical formula of a hydrocarbon if complete combustion or 5.400 mg of the hydrocarbon produced 18.254 mg of CO₂ and 3.736 mg of H₂O? Be sure to write C first in the formula.

empirical formula =

What is the molecular formula if the molar mass of the hydrocarbon is found to be about 70

molecular formula =

Answer 1

A hydrocarbon contains C and H only.

The molar masses of carbon dioxide and water are 44 g/mol and 18 g/mol respectively.

The molar mass in g/mol is also equal to the molar mass in mg/mmol.

18.254 mg of carbon dioxide corresponds to

0.41486 mmol of carbon dioxide also corresponds to 0.41486 mmol of C.

3.736 mg of water corresponds to

0.2076 mmol of water corresponds to of hydrogen atoms

The ratio of the number of mmol of C to the number of mmol of H atoms is 0.41486 : 0.4151 or 1:1.

Hence, the empirical formula of the hydrocarbon is CH.

The empirical formula mass is 12 + 1 =13 g/mol

The molar mass is about 70

Hence, the molecular formula is