Qualitative Analysis - Result Question 60

63. Gradual addition of $KI$ solution of $Bi\left(NO _3\right) _3$ solution initially produces a dark brown precipitate which dissolves in excess of $KI$ to give a clear yellow solution. Write chemical equations for the above reactions.

(1996, 2M)

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Solution:

On addition of $KI$ solution to a $Bi\left(NO _3\right) _3$ solution, firstly a dark brown precipitate of $BiI _3$ is formed that dissolve in excess of $KI$ forming a clear yellow solution of $BiI _4^{-}$:

$Bi^{3+}+3 I^{-} \longrightarrow \underset{\text { Dark brown }}{BiI _3 \downarrow} \xrightarrow{I^{-}} \underset{\text { Clear yellow solution }}{BiI_4^{-}}$