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 benczoic acid in acidic basic and neutral media according to the following redox equation
(i) acidic medium

in the laboratory benzoic acid is usually prepared by alkaline `KMnO_(4)` oxidation of toluene however in industry alcoholic `KMnO_(4)` is preferred to acid or alkaline `KMnO_(4)` 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^(-)ion)` are produced in the reaction itself
(ii) since rection occur faster in homogeneous medium than in heterogeneous medium therefore alcohol helps in mixing the two rectants i.e `KMnO_(4)` and toluene
(b) when conc `H_(2)SO_(2)` is added to an inorganic mixture containg chloride a pungent smelling gas hci is produced because a stronger acid displace a weaker acid from its salt
`2 NaCI+2H_(2)SO_(4)rarr2NaSO_(4)+2HCI`
`2 HCI+H_(2)SO_(4)rarrCI_(2)+SO_(2)+2H_(2)O`
however when the mixture contains bromide ion the initally produced HBr being a stronger reducing agent than HCI reduces `H_(2)SO_(4)` to `SO_(2)` and is itself oxidised to produce red vapour of `Br_(2)`
`2 NaBr +2 H_(2)SO_(4)rarr2NaHSO_(4)+2 HBr`
`2HBr+H_(2)SO_(4)rarrBr_(2)+SO_(2)+2H_(2)O`