Question

A metal nitrate reacts with $KI$ to give black precipitate which turns to orange on addition of $KI$ . Metal is

• A. $Hg^{2+}$
• B. $Bi^{3+}$
• C. $Pb^{2+}$
• D. $Cu^{+}$

Answer 1

Answer: (B)

$Bi^{3+}$

Answer 2

Since, the metal nitrate gives black ppt with $KI$ which in excess of $KI$ turns into orange, the metal must be $B i^{3+}$ and the reactions are as follows $B i^{3+}+3 I^{-} \rightarrow B i I_{3} \downarrow$ $Bi I _{3}+ I ^{-} \underset{\text{orange colour}}{[BiI_4^-]}$