JEE MAIN - Chemistry (2022 - 26th June Morning Shift - No. 11)
Which statement is not true with respect to nitrate ion test?
A dark brown ring is formed at the junction of two solutions.
Ring is formed due to nitroferrous sulphate complex.
The brown complex is [Fe(H2O)5 (NO)]SO4.
Heating the nitrate salt with conc. H2SO4, light brown fumes are evolved.
Explanation
Brown ring test
$$ \begin{aligned} &\mathrm{NO}_{3}^{-}+3 \mathrm{Fe}^{+2}+4 \mathrm{H}^{+} \rightarrow \mathrm{NO}+3 \mathrm{Fe}^{+3}+2 \mathrm{H}_{2} \mathrm{O} \\\\ &{\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+} \mathrm{NO} \rightarrow \underset{\text{Brown ring}}{\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{NO}]^{2+} \mathrm{H}_{2} \mathrm{O}\right.}} \end{aligned} $$
$$ \begin{aligned} &\mathrm{NO}_{3}^{-}+3 \mathrm{Fe}^{+2}+4 \mathrm{H}^{+} \rightarrow \mathrm{NO}+3 \mathrm{Fe}^{+3}+2 \mathrm{H}_{2} \mathrm{O} \\\\ &{\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+} \mathrm{NO} \rightarrow \underset{\text{Brown ring}}{\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{NO}]^{2+} \mathrm{H}_{2} \mathrm{O}\right.}} \end{aligned} $$
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