A translucent white waxy solid (A) on heating in an inert atmosph…

Question

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

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Answer

A = White phosphorus.
B = Red phosphorus.
C = Phosphine $(PH_3)$.
D = Phosphorus pentachloride $(PCl_5)$.
E = Phosphoric acid $(H_3PO_4)$.
Reactions are:
$\ \ \ \ \text{P}_4\text{(s)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow[\text{inert gas}]{\triangle \ \ \ }\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{P}_4\text{s}\\^\text{White phosphorus}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Red phosphorus}\\ \ \ \ \ \ \ \ \ ^\text{(A)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(B)}$
$\ \ \ \ \ \ \ \text{P}_4\text{(g)}\ \ \ +\ \ \ 3\text{KOH(aq)}+3\text{H}_2\text{O}\ \ \xrightarrow{\ \ \ \ \ \triangle\ \ \ \ \ \ }3\text{KH}_2\text{PO}_2\text{(aq)}\ \ \ \ +\ \ \ \text{PH}_3\text{(g)}\\^\text{White plasphorus}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Potassium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Phosphine}\\\ \ \ \ \ ^\text{(A)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{hypophosphite} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(C)}$
$\text{PH}_3\text{(g)}+4\text{Cl}_2\text{(g)}\rightarrow\text{PCl}_5\text{(g)}+3\text{HCl(g)}\\ ^\text{Phosphine}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Phosphorous}\\ \ \ \ \ ^\text{(C)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{pentachloride}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(D)}$
$\ \ \ \ \ \ \ \ \ \text{PCl}_5\text{(g)}\ \ \ \ \ \ \ \ \ \ \ \ + \ \ \ \ \ \ 4\text{H}_2\text{O(l)}\ \ \ \xrightarrow{\ \ \ \ \ }\ \ \ \text{H}_3\text{PO}_4\text{(aq)}\ \ \ +\ \ \ 5\text{Hcl(aq)}\\ ^\text{Phosphorous pentachloride}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Phosporic acid}\\ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(D)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(E)}$

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