8.12. How do you account 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 colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?

(a) Toluene can be oxidised to benzoic acid in acidic, basic and neutral media according to the following redox equations:

In the laboratory, benzoic acid is usually prepared by alcoholic KMnO₄ oxidation of toluene. However, in industry alcoholic KMnO₄ is preferred over acidic or alkaline KMnO₄ because of the following reasons:
(i) The cost of adding an acid or the base is avoided because in the neutral medium, the base (OH^- ions) are produced in the reaction itself.
(ii) Since reactions occur faster in homogeneous medium than in heterogeneous medium, therefore, alcohol helps in mixing the two reactants, i.e., KMnO₄

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(a) Toluene can be oxidised to benzoic acid in acidic, basic and neutral media according to the following redox equations:

In the laboratory, benzoic acid is usually prepared by alcoholic KMnO₄ oxidation of toluene. However, in industry alcoholic KMnO₄ is preferred over acidic or alkaline KMnO₄ because of the following reasons:
(i) The cost of adding an acid or the base is avoided because in the neutral medium, the base (OH^- ions) are produced in the reaction itself.
(ii) Since reactions occur faster in homogeneous medium than in heterogeneous medium, therefore, alcohol helps in mixing the two reactants, i.e., KMnO₄  (due to its polar nature) and toluene (because of its being an organic compound).

(b) KBr + H₂? SO₄? → KHSO₄? + HBr
HBr is a strong reducing agent which further reduces H₂? SO₄?  as follows
2HBr + H₂? SO₄? → Br₂? + SO₂? + H₂? O

But in case of mixture containing Chloride the reaction ends up on forming HCl as HCl is a weak reducing agent which can't further reducethe sulphuric acid further.
KCl+H₂? SO₄? →KHSO₄? +HCl? (colourless pungent smell gas)

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<p><strong> (a)</strong> Toluene can be oxidised to benzoic acid in acidic, basic and neutral media according to the following redox equations:</p><div><div><picture><source srcset="https://images.shiksha.com/mediadata/images/articles/1741861863phpw5Ds9I_480x360.jpeg" media=" (max-width: 500px)"><img src="https://images.shiksha.com/mediadata/images/articles/1741861863phpw5Ds9I.jpeg" alt="" width="365" height="81"></picture></div></div><p>In the laboratory, benzoic acid is usually prepared by alcoholic KMnO₄&nbsp;oxidation of toluene. However, in industry alcoholic KMnO₄&nbsp;is preferred over acidic or alkaline&nbsp;KMnO₄&nbsp;because of the following reasons:<br> (i) The cost of adding an acid or the base is avoided because in the neutral medium, the base (OH^- ions) are produced in the reaction itself.<br> (ii) Since reactions occur faster in homogeneous medium than in heterogeneous medium, therefore, alcohol helps in mixing the two reactants, i.e., KMnO₄&nbsp; (due to its polar nature) and toluene (because of its being an organic compound).</p><p><strong> (b) </strong>KBr + H₂? SO₄? → KHSO₄? + HBr<br>HBr is a strong reducing agent which further reduces&nbsp;H₂? SO₄? &nbsp;as follows<br>2HBr + H₂? SO₄? → Br₂? + SO₂? + H₂? O</p><p>But in case of mixture containing Chloride the reaction ends up on forming&nbsp;HCl&nbsp;as&nbsp;HCl&nbsp;is a weak reducing agent&nbsp;which can't further reducethe sulphuric acid further.<br>KCl+H₂? SO₄? →KHSO₄? +HCl? (colourless pungent smell gas)</p>

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