Qualitative Analysis - Result Question 61

####64. A scarlet compound A is treated with conc. HNO3 to give a chocolate brown precipitate B. The precipitate is filtered and the filtrate is neutralised with NaOH. Addition of KI to the resulting solution gives a yellow ppt C. The brown ppt B on warming with conc. HNO3 in the presence of Mn(NO3)2 produces a pink coloured solution due to the formation of D. Identify A,B,C and D. Write the reaction sequence.

(1995, 4M)

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Solution:

  1. A(Pb3O4) Scarlet CHNO3B(PbO2) Chocolate  Filtered Pb(NO3)2 Filtrate 

Filtrate is neutralised with NaOH and on reaction with KI, gives yellow ppt of PbI2.

Pb(NO3)2+2KIPbI2 Yellow +2KNO3

PbO2 on warming with conc. HNO3 in presence of Mn(NO3)2 produced pink solution due to formation of Pb(MnO4)2 (I).

5PbO2+2Mn(NO3)2+4HNO3Pb(MnO4)2 +4Pb(NO3)2+2H2O A=Pb3O4,B=PbO2,C=PbI2 and D=Pb(MnO4)2.



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