0.2 mol of hydrocarbons undergo complete combustion to give 35.2 of carbon dioxide and 14.4g of water as the only product. What is the molecular formula of hydrocarbon

.

Explanation:

Look up the relative atomic mass of , , and on a modern periodic table:

Calculate the molecular mass of and :

;

.

Given the mass of and produced, calculate the number of moles of molecules that were produced:

;

.

Calculate the number of moles of atoms and atoms in these and molecules.

The combustion reaction here include two reactants: the hydrocarbon and .

As the name suggests, hydrocarbons contain only atoms and atoms. On the other hand, contains only atoms.

Therefore, all the and atoms in those and molecules are from the unknown hydrocarbon. (With a similar logic, all the atoms in those combustion products are from .)

In other words, that of this unknown hydrocarbon molecules contains:

Hence, each of these hydrocarbon molecules would contain carbon atoms and hydrogen atoms.

The molecular formula of this hydrocarbon would be .