Question

What are hydrocarbons? Write the name and general formula (i) saturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?

Answer 1

The organic compounds consisting of Carbon ($\mathrm{C}$) and Hydrogen ($\mathrm{H}$) atoms are known as hydrocarbons. They are of two types depending on the kind of bonds formed between carbon-carbon atoms:

1. Saturated hydrocarbons
2. Unsaturated hydrocarbons

Saturated hydrocarbons:

The organic compounds containing carbon atoms have a single bond between two carbon atoms are called saturated hydrocarbons.

(i) Alkanes are saturated hydrocarbons that contain only single bonds between $\mathrm{C}$ and $\mathrm{H}$ atoms.

(ii) The general formula is saturated hydrocarbons is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$.

(iii) Ethane and propane are called saturated hydrocarbons.

The structure of ethane and propane is represented as below:

${\mathrm{CH}}_3-{\mathrm{CH}}_3$, ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_3$

The organic compounds containing carbon atoms having multiple bonds either double bond or triple bonds between two carbon atoms are called unsaturated hydrocarbons.

(i) Alkenes and alkynes are unsaturated hydrocarbons that contain double bonds and triple bonds between the $\mathrm{C}$ and $\mathrm{H}$ atoms.

(ii) The general formula of alkene is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$ and for alkyne is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$.

(iii) Ethene and ethyne are called unsaturated hydrocarbons.

(iv) The structure of ethene is written as ${\mathrm{CH}}_2={\mathrm{CH}}_2$ and the structure of ethyne is $\mathrm{CH}\equiv \mathrm{CH}$.

(i) The unsaturated hydrocarbon could be converted into saturated hydrocarbon by breaking the double bond of the unsaturated hydrocarbons.

(ii) The addition reaction in which hydrogen is added to unsaturated hydrocarbon in the presence of Nickel ($\mathrm{Ni}$) or Platinum ($\mathrm{Pt}$) catalyst gives the saturated hydrocarbons.

The conversion of unsaturated hydrocarbons to saturated hydrocarbons is written as:

. ${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{H}}_2\stackrel{\mathrm{Ni},\mathrm{heat}}{\to }{\mathrm{CH}}_3-{\mathrm{CH}}_3$