Question

A translucent white waxy solid (A) on heating in an inert atmosphere is converted into 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 (C) forms (D) which hydrolyses to compound (E). Identify (A) to (E)
CBSE 1999 Class 12th

Answer 1

Hey !!

(i) Since a translucent white waxy solid (A), on heating in an inert atmosphere, is converted into its allotrope (B), therefore, (A) is white or yellow phosphorous while (B) is red phosphorous.

                P₄ (s) ----->(Heat, inert gas) P₄ (s)

 (White phosphorous)               (Red phosphorous)

(ii) Since allotrope (A) on boiling with dilute aqueous KOH gives a highly poisonous gas (C) having rotten fish smell, therefore, it is confirmed that ''allotrope'' is white phosphorous gas (C) is phosphine (PH₃)

             P₄ (s) + 3 KOH (aq) + 3 H₂O (l) --(Heat)--> 3 KH₂PO₂ + PH₃

(White phosphorus)                         (Pot. hypophosphite) (Phosphine) (C)

(iii) Since phosphine (C) reacts with excess of chlorine to form a compound (D) which upon hydrolysis gives compound (E), therefore, (D) must be phosphorous (PCl₅) and (E) must be phosphoric acid (H₃PO₄)

          PH₃ (g) + 4 Cl₂ (g) ------> PCl₅ + 3 HCl (g)

Phosphine (C)  (Excess)    (Phosphorous pentachloride) (D)

        PCl₅ (s) + 4 H₂O (l) -----> H₃PO₄ (aq) + 5 HCl

          (D)                             (Phosphoric acid) (E)

Thus, (A) is white phosphorus (B) is red phosphorous (C) is phosphine (PH₃). (D) is phosphorus pentachloride and (E) is phosphoric acid (H₃PO₄)

GOOD LUCK !!

Answer 2

Hello! Dear User!

Answer!

>>>>Translucent waxy solid is actually white phosphorus  (P4)

>>>>P4 on heating gives red phosphorus in inert atmosphere

>>>>P4 on reaction with KOH gives phosphine , a poisonous gas

 >>>>  P4   +  KOH + H2O ⇒   PH3 + KH2PO2

>>>>Now P4 on excess of chlorine  gives PCl5 which on hydrolysis gives POCl3 and H3PO4

>>>>>P4 + 10Cl2 ⇒  4PCl5

>>>>>PCl5 + H2O ⇒ POCl3 + 2HCl

>>>>POCl3 + 3H2O ⇒  H3PO4  +  3HCl

 

A :  (white phosphorus)

B :  (red )phosphorous

C :  (Phosphine (PH₃)

D :  (Phosphorus pentachloride)

E : (Phosphoric acid (H₃PO₄)

Hope This Helps You!

Have a great day!

Thanks for question!