How do you count 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 balanced redox equation for the reaction.
b) When concentrated sulphuric acid is added to 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) Balanced equation of `KMnO_(4)//H^(+)` ( Acidic medium )
`MnO_(4)^(-)+8H^(+)+5e^(-)to Mn^(+2)+4H_(2)O`
Balanced equation of `KMnO_(4)//OH^(_)` (Basic medium)
`MnO_(4)^(-)+2 H_(2)O+3 e^(-)to MnO_(2)+4 OH^(-)` `to` Toluene is oxidised to benzoic acid in alcoholic medium.
`to` Toluene is easily oxidised in presence of alcoholic `KMnO_(4)`

(b) When Conc `H_(2)SO_(4)` reacts with NaCl then HCl vapours are evolved.
`2 NaCl+H_(2)SO_(4)to Na_(2)SO_(4)+2 HCl `
When Conc. `H_(2)SO_(4)` reacts with KBr than HBr vapours are evolved which on further oxidation given reddish brown `Br_(2)` vapours. `2 KBr+H_(2)SO_(4)to Na_(2)SO_(4)+2 HBr`
`2 MBr + H_(2)SO_(4)to 2 H_(2)O+SO_(2)+Br_(2)` (Reddish brown)