How do you count for the following observations?

(a) Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.

(b) When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colorless pungent smelling gas HCl , but if the mixture contains bromide then we get red vapour of bromine. Why?

Asked by Pragya Singh | 1 year ago |  54

##### Solution :-

(a) While manufacturing benzoic acid from toluene, alcoholic potassium permanganate is used as an oxidant due to the given reasons.

(i) In a neutral medium, $$OH^{ – }$$ ions are produced in the reaction. Due to that, the cost of adding an acid or a base can be reduced.

(ii) $$KMnO_{ 4 }$$​ and alcohol are homogeneous to each other as they are polar. Alcohol and toluene are homogeneous to each other because both are organic compounds. Reactions can proceed at a faster rate in a homogeneous medium compared to heterogeneous medium. Therefore, in alcohol,

$$KMnO_{ 4 }$$​ and toluene can react at a faster rate.

(b) When concentrated $$H_{ 2 }SO_{ 4 }$$​ is added to an inorganic mixture containing bromide, firstly HBr is produced. HBr, a strong reducing agent, reduces $$H_{ 2 }SO_{ 4 }$$​ to $$SO_{ 2 }$$​ with the evolution of bromine’s red vapour.

$$2 \; NaBr \; + \; 2 \; H_{ 2 }SO_{ 4 } \; \rightarrow \; 2 \; NaHSO_{ 4 } \; + \; 2 \;$$

$$2 \; HBr \; + \; H_{ 2 }SO_{ 4 } \; \rightarrow \; Br_{ 2 } \; + \; SO_{ 2 } \; + \; 2 \; H_{ 2 }$$

When concentrated $$H_{ 2 }SO_{ 4 }$$ I added to an inorganic mixture containing chloride, a pungent smelling gas (HCl) is evolved. HCl, a weak reducing agent, cannot reduce $$H_{ 2 }SO_{ 4 }$$ to $$SO_{ 2 }$$.

$$2 \; NaCl \; + \; 2 \; H_{ 2 }SO_{ 4 } \; \rightarrow \; 2 \; NaHSO_{ 4 } \; + \; 2 \;$$

Answered by Abhisek | 1 year ago

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