Question

How do you calculate the empirical formula of a hydrocarbon?

Answer 1

The empirical formula of a chemical compound is the simplest positive integer ratios of atoms present in a compound. Firstly, we have to determine the mole ratio of each element from the mass. Although different chemical species can also have the same empirical formula.

Complete step by step answer:
A hydrocarbon is an organic compound consisting entirely of hydrocarbon and carbon. The majority of hydrocarbons found on earth occur in petroleum, coal and natural gas. Petroleum and coal are generally thought to be products of decomposition of organic matter. In contrast to petroleum is coal. Which is richer is carbon? Porrek in hydrogen.
An empirical formula makes no mention of the arrangement of the number of atoms. It is standard for many ionic compounds. For a given chemical compound their empirical formula remains the same through its molecules of a chemical compound are not the same. The structural formulas show the arrangement of the molecule. It is also possible for different types of compounds to have equal empirical formulas.
Step to calculate: To determine empirical formulas assume that we have $100$ grams of the compound.
(1) Change each percentage to an expression of the mass of each element in grams.
(2) Convert the amount of each element in grams to its amount.
(3) divide each of the resulting values by the smallest values among them.
(4) If necessary, multiply these numbers by integers in order to get whole numbers.
In general there are three types of hydrocarbons depending on the covalent bonds.
(1) Alkanes: An alkane consists of hydrogen and carbon atoms arranged in a structure in which all the carbon-carbon bonds are single. Alkanes have general formula ${C_n}{H_{2n + 2}}$
E.g. Methane with $n = 1$ formula $C{H_4}$
(2) Alkenes: Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. These with double bonds are called alkenes. They hence the formula ${C_n}{H_{2n}}$
Example: ${C_2}{H_4}$
(3) Alkynes: Unsaturated hydrocarbon with triple bonds between carbon atoms. Formula for those with one triple bond ${C_n}{H_{2n - 2}}$
Example: ${C_2}{H_2}$ Acetylene or ethyne.
Example:-
Consider $1.71gC\& 0.287gH$ molecular mass of $C = 12.01g\& H = 1.008g$
$1.171gC \times \dfrac{{1molC}}{{12.01gC}} = 0.142mol.C$
$0.287gH \times \dfrac{{1mol.H}}{{1.008gH}} = 0.284mol.H.$
We get the hydrocarbon as ${C_{0.142}}{H_{0.284}}$
Divide both by smaller subscript we get,
$\dfrac{{{C_{0.142}}}}{{0.142}}\dfrac{{{H_{0.284}}}}{{0.142}} \Rightarrow C{H_2}$

**Thus the empirical formula for the compound is $C{H_2}$ which may not be its molecular formula.
**

Additional Information:
Aromatic hydrocarbons, also known as arenas, are hydrocarbons that have at least one aromatic ring. Hydrocarbons can be gases, liquids, waxes or low melting solids or polymers. Lakes of liquid methane and ethane have been found on Titan, Saturn’s largest moon, confirmed by the Cassini Huygens Mission. Petroleum derived hydrocarbons are mainly consumed to fuel, but they are also the source of virtually all synthetic organic compounds, including plastics and pharmaceuticals.

Note: Hydrocarbons are introduced into the environment through extensive use as fuels and chemicals as well as through leaks of accidental spills during exploration, production, refining or transport of fossil fuels. Crude oil and natural gas are the two largest sources of hydrocarbon contamination of soil. Aromatic compounds such as benzene are narcotic and chronic toxins and are carcinogenic.