(a) Give chemical tests to distinguish between compounds in the following pairs of substances ,
(i) Ethanal and Propanal
(ii) Benzoic acid and Ethyl benzoate
(b) An organic compound contains `69.77%` carbon , `11.63%` hydrogen and rest oxygen . The molecular mass of the compound is 86. It does not reduce Tollen 's reagent but forms an addition compound with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acids . Derive the structure of the compound.

Explanation

(a) (i) Distinction between Ethanal and Propanal : Ethanal `(CH_(3)CHO)` and propanal `(CH_(3)CH_(2)CHO)` can be distinguished by the iodoform test . Ethanal reacts with `I_(2)//NaOH(orNaOI)` to give yellow ppt . Of iodoform but propanal does not react with `I_(2)//NaOH`.
`underset("Ethanal")(CH_(3)CHO+3I_(2))+4NaOHoverset(Delta)toHCOONa+underset(("Yellow ppt."))(CHI_(3))+3NOI+3H_(2)O`
`underset("Propanal")(CH_(3)CH_(2)CHO)overset(I_(2)//NaOH)to` No Yellow ppt. of `CHI_(3)`
(ii) Benzoic acid and Ethyl benzoate : These compounds can be distinguished by using `NaHCO_(3)` test . Benzoic acid produces brisk effervescene with `NaHCO_(3)` solution while ethyl benzoate does not .
`underset("Benzoic acid")(C_(6)H_(5)COOH)+NaHCO_(3)tounderset("Sod . benzoate")(C_(6)H_(5)COONa+CO_(2)+H_(2)O)`
`C_(6)H_(5)COOC_(2)H_(5)overset(NaHCO_(3)"Soln.")to` No effervescence due to evolution of `CO_(2)` gas.