When 13.0 g of a hydrocarbon are burned in excess O2, 9.0 g of H2O are formed. What is the formula of the hydrocarbon?

CH

Explanation:

When a hydrocarbon burns, there are only two products. These are hydrogen and carbon iv oxide. The general equation for burning a hydrocarbon is shown below:

Fuel + O2 → CO2 + H2O

Since 9g Of water is formed, we can get the number of moles of hydrogen and the mass of hydrogen.

We now need to get the actual moles of carbon and hydrogen in the hydrocarbon to know what the chemical formula is.

The number of moles of hydrogen and its mass can be obtained from that of water. The number of moles of water is simply the mass of water divided by the molar mass. The molar mass of water is 18g/mol. The number of moles is thus 9/18 which is 0.5. Since there are two atoms of hydrogen in one molecule of water, the number of moles of hydrogen is thus 2 * 0.5 which equals one mole.

The mass of hydrogen is thus the number of moles of hydrogen * the molar mass of hydrogen which is

1 * 1 = 1g

Hence, the mass of the carbon in the hydrocarbon is 13 - 1 = 12g

The number of moles of carbon present is thus 12/12 which equals 1.

Since the mole ratio is 1 to 1, the formula of the hydrocarbon is thus CH