Qualitative Analysis - Result Question 50

####53. When a white crystalline compound X is heated with K2Cr2O7 and concentrated H2SO4, a reddish brown gas A is evolved. On passing A into caustic soda solution, a yellow coloured solution B is obtained. Neutralising the solution of B with acetic acid and on subsequent addition of lead acetate a yellow precipitate C is obtained.

When X is heated with NaOH solution, colourless gas is evolved and on passing this gas into K2HgI4 solution, a reddish brown precipitate D is formed. Identify A,B,C,D and X. Write the equations of reactions involved.

(2002)

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Solution:

  1. X=NH4Cl;A=CrO2Cl2;B=Na2CrO4;C=PbCrO4;

D=H2N(HgO)HgI.

Reactions involved :

(i) 4NH4Cl(X)+K2Cr2O7+6H2SO42CrO2Cl2(A)

+4NH4HSO4+2KHSO4+3H2O

(ii) CrO2Cl2(A)+2NaOHNa2CrO4(B)+2HCl

(iii) Na2CrO4(B)+(CH3COO)2PbPbCrO4(C)

+2CH3COONa

(iv) NH4Cl(X)+NaOHNaCl+H2O+NH3

(v) 2K2HgI4+NH3+3KOHH2N(HgO)HgI(D)

+7KI+2H2O



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