JEE MAIN - Chemistry (2024 - 6th April Evening Shift - No. 3)
During the detection of acidic radical present in a salt, a student gets a pale yellow precipitate soluble with difficulty in $$\mathrm{NH}_4 \mathrm{OH}$$ solution when sodium carbonate extract was first acidified with dil. $$\mathrm{HNO}_3$$ and then $$\mathrm{AgNO}_3$$ solution was added. This indicates presence of :
$$\mathrm{I}^{-}$$
$$\mathrm{CO}_3{ }^{2-}$$
$$\mathrm{Cl}^{-}$$
$$\mathrm{Br}^{-}$$
Explanation
The $$\mathrm{Br}^{-}$$ ion present in the salt gives pale yellow ppt. of $$\mathrm{AgBr}$$ with $$\mathrm{AgNO}_3$$, insoluble in dil $$\mathrm{HNO}_3$$ but partially soluble in aq. $$\mathrm{NH}_4 \mathrm{OH}$$.
$$\mathrm{Br}^{-}+\mathrm{AgNO}_3 \rightarrow \underset{\text { Pale yellow }}{\mathrm{AgBr} \downarrow}+\mathrm{NO}_3^{-}$$
$$\mathrm{AgBr}+2 \mathrm{NH}_4 \mathrm{OH} \rightarrow \underset{\text { Partially soluble }}{\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right] \mathrm{Br}}+2 \mathrm{H}_2 \mathrm{O}$$
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