Question

$p$-Amino- $N,N$-dimethylaniline is added to a strongly acidic solution of $X$. The resulting solution is treated with a few drops of aqueous solution of $Y$ to yield blue, coloration due to the formation of methylene blue. Treatment of the aqueous solution of $Y$ with the reagent potassium hexacyanoferrate(II) leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly, treatment of the solution of $Y$ with the solution of potassium hexacyanoferrate(III) leads to a brown coloration due to the formation of $Z$.

The compound $Y$ is

• A. $MgC{l}_2$.
• B. $FeC{l}_2$
• C. $FeC{l}_3$
• D. $ZnC{l}_2$

Answer 1

Answer: (C)

$\underset{(X)}{N{a}_2}S+2H^{+}\to H_{2}S+2N{a}^{+}$

$4FeC{l}_3+3K_4[\stackrel{II}{F}e(CN{)}_6]\to \underset{\text{Intence blue}}{F{e}_4[Fe(CN{)}_6{]}_3}+2KCl$
$FeC{l}_3+K_3[Fe(CN{)}_6]\to \underset{\text{Brown coloration}}{Fe[Fe(CN{)}_6]}+3KCl$
$(Y)-FeC{l}_3$