Qualitative Analysis - Result Question 50
####53. When a white crystalline compound $X$ is heated with $K _2 Cr _2 O _7$ and concentrated $H _2 SO _4$, 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 $K _2 HgI _4$ solution, a reddish brown precipitate $D$ is formed. Identify $A, B, C, D$ and $X$. Write the equations of reactions involved.
(2002)
Show Answer
Solution:
- $X=NH _4 Cl ; A=CrO _2 Cl _2 ; B=Na _2 CrO _4 ; C=PbCrO _4$;
$D=H _2 N(HgO) HgI$.
Reactions involved :
(i) $4 NH _4 Cl(X)+K _2 Cr _2 O _7+6 H _2 SO _4 \longrightarrow 2 CrO _2 Cl _2(A)$
$$ +4 NH _4 HSO _4+2 KHSO _4+3 H _2 O $$
(ii) $CrO _2 Cl _2(A)+2 NaOH \longrightarrow Na _2 CrO _4(B)+2 HCl$
(iii) $Na _2 CrO _4(B)+\left(CH _3 COO\right) _2 Pb \longrightarrow PbCrO _4 \downarrow(C)$
$+2 CH _3 COONa$
(iv) $NH _4 Cl(X)+NaOH \longrightarrow NaCl+H _2 O+NH _3$
(v) $2 K _2 HgI _4+NH _3+3 KOH \longrightarrow H _2 N(HgO) HgI(D)$
$$ +7 KI+2 H _2 O $$
