Question

An aqueous solution of a salt X turns blood red on treatment with SCN${}^{-}$ and blue on treatment with K${}_4$[Fe(CN)${}_6$]. X also gives a positive chromyl chloride test. The salt $X$ is:

• A. Cu(NO${}_3$)${}_2$
• B. FeCl${}_3$
• C. CuCl${}_2$
• D. Fe(NO${}_3$)${}_3$

Answer 1

The correct option is B FeCl${}_3$

The salt X is ferric chloride $FeC{l}_3$.
It reacts with $SC{N}^{-}$ to form blood red ferric thiocyanate.
$FeC{l}_3+3SC{N}^{-}\stackrel{F}{\to }e(CNS{)}_3+3C{l}^{-}$
It also reacts with potassium ferrocyanide to form blue colored ferric ferrocyanide.
$4FeC{l}_3+3K_4\left[Fe\right(CN{)}_6\left]\stackrel{F}{\to }{e}_4\right[Fe(CN{)}_6{]}_3+12KCl$
Also, since, salt X contains chlorine, it gives positive chromyl chloride test.
$4C{l}^{-}+K_{2}C{r}_2{O}_7+3H_{2}S{O}_4\to K_{2}S{O}_4+2S{O}_4^{2-}+2Cr{O}_{2}C{l}_2\uparrow +3H_{2}O$
In this test, orange yellow chromyl chloride gas is obtained.