Question

Which of the following statement is/are true about the characteristic properties of alkanes?

• A. Boiling point increase with a molecular mass
• B. All alkane are saturated hydrocarbon
• C. They mostly show substitutions reaction with halogens.
• D. All of these

Answer 1

The correct option is D

All of these

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

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

Alkanes are saturated hydrocarbons that contain only single bonds between C and H atoms.

Ethane and propane are called saturated hydrocarbons.

(ii) The boiling point of alkanes increases with an increase in molecular mass because as the carbon chain gets longer (high molecular mass) the intermolecular London Dispersion forces are more, and this is responsible for increasing the boiling point of alkanes.

Example: The boiling point of n-hexane (${\mathrm{C}}_6{\mathrm{H}}_{14}$) is $69°\mathrm{C}$ and the boiling point of n-heptane (${\mathrm{C}}_7{\mathrm{H}}_{16}$) is $98.42°\mathrm{C}$.

(iii) Haloalkanes are produced, when alkane reacts with halogens with the substitution of hydrogen atoms.

Example: In the presence of light, the bromination of Ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) forms Bromoethane (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Br}$) and Hydrogen bromide ($\mathrm{HBr}$) as the major product.

The reaction is written as:

$$\begin{gathered} {\mathrm{CH}}_3-{\mathrm{CH}}_3+{\mathrm{Br}}_2\stackrel{\mathrm{Heat}\mathrm{or}\mathrm{Light}}{\to }{\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{Br}+\mathrm{HBr} \\ \left(\mathrm{Ethane}\right)\left(\mathrm{Bromine}\right)(\mathrm{Bromoethane})(\mathrm{Hydrogen}\mathrm{bromide}) \end{gathered}$$

Thus, all the three statements are correct with respect to alkanes.

Hence, option (D) is the correct option.