Question

Chlorine reacts with saturated hydrocarbons at room temperature in the

• A. Absence of sunlight
• B. Presence of sunlight
• C. Presence of water
• D. Presence of hydrochloric acid

Answer 1

The correct option is B

Presence of sunlight

The explanation for the correct option:

Option (B): the presence of sunlight

1. A chemical reaction that involves the addition of one or more halogens to a compound is known as halogenation.
2. The halogen molecule is broken down into free radicals by ultraviolet light, which starts the process. The homolytic fission of the chlorine molecule into the chlorine radical is caused by ultraviolet radiation. $\underset{\mathrm{Chlorine}}{{\mathrm{Cl}}_2}\stackrel{\mathrm{Sunlight}}{\to }\underset{\mathrm{Chlorine}\mathrm{radical}}{2\mathrm{Cl}}$
3. The radical then attacks saturated hydrocarbons, resulting in the formation of haloalkanes.
4. All alkane substitution reactions, such as chlorination and bromination, take place in the presence of light. Example chlorination of methane$\underset{\mathrm{Methane}}{{\mathrm{CH}}_4}+\underset{\mathrm{Chlorine}}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}\stackrel{\mathrm{sunlight}}{\to }\underset{\mathrm{Chloromethane}}{{\mathrm{CH}}_3\mathrm{Cl}}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{l}\right)}$
5. Hence, it is the correct option.

The explanation for incorrect options:

Option (A): Absence of sunlight

1. Reactions that involve the addition of halogen in an organic compound are known as halogenation reactions.
2. The halogen in the reaction needs UV rays to break the halogen atom in its free radical and sunlight is a good source of UV rays.
3. Therefore, in absence of sunlight, no halogenation reaction takes place.

Option (C): Presence of Water.

1. Water is a source of hydrogen and hydroxide ions. Reactions like hydration reactions, dehydration reactions, etc. require water.
2. Reactions that involve the addition of halogen are known as halogenation reactions. The halogen in these reactions requires a source of UV radiation to break the halogen atom into its radical.
3. Water is not a source of UV radiation.
4. Hence, it is an incorrect option.

Option(D): Presence of Hydrochloric acid

1. Hydrochloric acid is a strong acid that dissociates to give hydrogen and chloride ion.
2. A halogenation reaction requires UV radiation to break its halogen into a free radical. Therefore, Hydrochloric acid is not a source of UV radiation.
3. Hence, it is the incorrect option.

Therefore, chlorine reacts with saturated hydrocarbons at room temperature in the presence of sunlight.