(a) Write chemical equations to illustreate the following name bearing reactions : (i) Cannizzaro 's reaction
(ii) Hell - Volhard -Zelinsky reaction
(b) Given chemical tests to distinguish between the following pairs of compounds : (i) Propanal and Propanone
(ii) Acetophenone and Ben - zophenone
(iii) Phenol and Benzoic acid

Explanation

(a) (i) Cannizzaro reaction : Aldehydes which do not contain an `alpha` - hydrogen atom , when treated with concentrated alkali solution undergo self oxidation - reduction . As a result , one molecule of the aldehyde is reduced to the corresponding alcohol which is oxidised to the corresponding carboxylic . this reaction is called Cannizzaro reaction.
`underset("Benzaldehyde")(C_(6)H_(5)CHO)+underset((50%))(NaOH)tounderset("Benzyl alcohol")(C_(6)H_(5)CH_(2)OH)+underset("Sod . benzoate")(C_(6)H_(5)COONa)`
(ii) Hell Volhard -Zelinsky Reaction : Carboxylic acids react with chlorine or bromine in the presence of red phosphorous to give compounds in which `lambda` - hydrogen atom is replaced by halogen atom.
`underset("acetic acid")(CH_(3)COOH+Cl_(2))overset(P)tounderset("chloro acetic acid")(ClCH_(2)COOH+HCl)`
`ClCH_(2)COOH+Cl_(2)overset(P)tounderset("Dichloro acetic acid")(Cl_(2)CHCOOH+HCl)`
`Cl_(2)CHOOH+Cl_(2)overset(P)tounderset("Trichloro acetic acid")(Cl_(2)C COOH+HCl)`
(b) (i) Propanal and propanone can be distinguish by Tollen 's test . Propanal will form the silver mirror . Propanal give this test but propanone (Ketones) do not respond to these test.
`RCHO+2[Ag(NH_(3))_(2)]^(+)+3OH^(-)toRCOO^(-)+underset("Silver mirror")(2Ag+2H_(2)O)+4NH_(3)`
(ii) Iodoform Test : Acetophenone has `CH_(3)CO` - group which on treatment with NaOl given iodoform and a salt of carboxylic acid

(iii) Distinction between phenol and Benzoic acid : Phenol gives a violet colouration with nevtral `FeCl_(3)` solution while benzoic acid gives buff coloured ppt . of ferric benzoate
`underset("Phenol")(3C_(6)H_(5)OH+FeCl_(3))to underset("Violet colouration")((C_(6)H_(5)O)_(3)Fe+3HCl)`
`underset("Benzoic acid ")(3C_(6)H_(5)COOH+FeCl_(3))tounderset("Buff coloured ppt ")((C_(6)H_(5)COO)_(3)Fe+3HCl)`