JEE Main 2022 — Chemistry Inorganic Chemistry

2022mcqmedium

${\mathrm{Fe}}^{3+}$ cation gives a prussian blue precipitate on addition of potassium ferrocyanide solution due to the formation of

Official previous-year question

Held on 27 Jul 2022 · Verified 6 Jul 2026.

Options

A
${[\mathrm{Fe}{({H}_{2}O)}_{6}]}_{2}[\mathrm{Fe}{(\mathrm{CN})}_{6}]$
B
${\mathrm{Fe}}_{2}{[\mathrm{Fe}{(\mathrm{CN})}_{6}]}_{2}$
C
${\mathrm{Fe}}_{3}{[\mathrm{Fe}{(\mathrm{OH})}_{2}{(\mathrm{CN})}_{4}]}_{2}$
D
${\mathrm{Fe}}_{4}{[\mathrm{Fe}{(\mathrm{CN})}_{6}]}_{3}$

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Solution

Ferric ion forms a prussian blue precipitate due to the formation of $F{e}_{4}{[Fe{(CN)}_{6}]}_{3}$ . In this method, to a portion of sodium fusion extract, freshly prepared ferrous sulphate $FeS{O}_{4}$ solution is added and warmed. Then about $2$ to $3$ drops of $FeC{l}_{3}$ solution are added and acidified with conc. $HCl$ . The appearance of a prussian blue colour indicates the presence of nitrogen.

$FeS{O}_{4}+2NaOH\rightarrow Fe{(OH)}_{2}+N{a}_{2}S{O}_{4}$

$6NaCN+Fe{ ( OH )}_{2} \rightarrow \underset{ \text{Sodium} \text{ferrocyanide}}{ N{a}_{4} [ Fe{ ( CN )}_{6} ]} +2NaOH$

$3N{a}_{4} [ Fe{ ( CN )}_{6} ]+4FeC{l}_{3} \rightarrow \underset{\begin{matrix} \text{Ferric ferrocyanide} \\ ( \text{prussian} \text{blue} ) \end{matrix}}{ F{e}_{4} { [ Fe{ ( CN )}_{6} ]}_{3} } +12NaCl$

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Options

${[\mathrm{Fe}{({H}_{2}O)}_{6}]}_{2}[\mathrm{Fe}{(\mathrm{CN})}_{6}]$

${\mathrm{Fe}}_{2}{[\mathrm{Fe}{(\mathrm{CN})}_{6}]}_{2}$

${\mathrm{Fe}}_{3}{[\mathrm{Fe}{(\mathrm{OH})}_{2}{(\mathrm{CN})}_{4}]}_{2}$

${\mathrm{Fe}}_{4}{[\mathrm{Fe}{(\mathrm{CN})}_{6}]}_{3}$

Solution

$FeS{O}_{4}+2NaOH\rightarrow Fe{(OH)}_{2}+N{a}_{2}S{O}_{4}$

$6NaCN+Fe{ ( OH )}_{2} \rightarrow \underset{ \text{Sodium} \text{ferrocyanide}}{ N{a}_{4} [ Fe{ ( CN )}_{6} ]} +2NaOH$

JEE Main 2022 — Chemistry Inorganic Chemistry

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JEE Main 2022 — Chemistry Inorganic Chemistry

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