Question

A translucent white waxy solid (A) on heating in an inert atomosphere is converted to its allotropic form (B). The solid (A) on reaction with very dilute aqueous KOH liberates a highly poisonous gas (C ) having rotten fish smell. With excess of chlorine, (A) forms (D) which hydrolyses to compound (E ). Identify compounds (A) to (E ).

Answer 1

The data suggests that the white waxy solid (A) is white phosphorus and its allotropic form (B) is red phosphorus. ON reacting with dilute KOH solution, the poisonous gas (C ) that is liberated is phosphine `(PH_(3))`. With excess of chlorine, (A) forms phosphorus pentachloride `(PCl_(5))` which upon hydrolysis gives orthophosphoric acid. The reactions involved in the formation of the above listed compounds are as follows :
(i) `underset("White phosphorus (A)") (P_(4)) overset(CO_(2)("inert")) to underset("Red Phosphorus (B)") (P_(4))`
(ii) `underset((A))(P_(4))+3KOH +3H_(2)O to underset("Pot. Hypophosphite")(3KH_(2)PO_(2)) +underset("Phosphine (C )")(PH_(3))`
(iii) `underset((A))(P_(4)) + underset(("Excess"))(10 Cl_(2)) to underset((D))(4PCl_(5))`
(iv)` PCl_(5)+4H_(2)O to underset("Orthophosphoric acid "(E ))(H_(3)PO_(4))+5HCl`