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

Explanation

(a) Toluene can be oxidised to bemzopic acid in acidic alkanline and neutral medium by uising potassium permangant
(i) In acidic medium:
`MnO_(4)^(-)(aq)+8H^(+)(aq)+5e^(-)rarrMn^(2+)(aq)+4H_(2)O(l)xx6`

In the manufacture of bemnzoic acid from toluene, neutral medium is preferred over acidic or alkaline medium due to following reasons
In the neutral medium, neither acid or base is to be added externally .This wil definitely reduce the cost opf the manufcturing process.
Alcohol if used as solvent will hgelp in the lformation of a homogenous mixture between toluene(non polar) and `KMnO_(4)` (ionic).Actually alcohol has non polar alkyl group as well as polar OH group
(b) A chloride such as NaCI reacts with concentrated suphhuric acid to elvolve hydrogen chloride gas upon heatin.It has a pungent smell.
`NaCI(s)+H_(2)SO_(4)(aq)rarrNaHSO_(4)(aq)+HBr(g)xx2`
`{:((H_(2)SO_(4)(aq)rarr+H_(2)(aq)+SO_(2)(g)+0),(2HBr(g)+Orarr+H_(2)O(aq)+Br_(2)(g)))/(2NaBr(s)+3H_(2)SO_(4)(aq)rarr2NaHSO_(4)(aq)+2H_(2)O(aq)+SO_(2)+Br_(2)(g)):}`
Please note HCI (g) is quite stable and is not oxidised to chlorine with concentrated suphuric acid.