The prussian blue colour obtained during the test of nitrogen by Lassaigne's test is due to the formation of :

The prussian blue colour obtained during the test of nitrogen by Lassaigne's test is due to the formation of :
  1. \(\mathrm{Fe}\left[\mathrm{Fe}(\mathrm{CN})_{6}ight]_{3}\)
  2. \(\mathrm{Na}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}ight]\)
  3. \(\mathrm{Fe}(\mathrm{CN})_{3}\)
  4. \(\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6} ight]_{3}\)

Solution

Reaction takes place in Lassaigne's test are as:
\(\mathrm{N a}+\mathrm{C}+\mathrm{N} \longrightarrow \mathrm{N} \mathrm{a} \mathrm{C N}\)
\(\mathrm{6 N a C N}+\mathrm{F} \mathrm{e S O}_{4} \longrightarrow \mathrm{N a}_{4}\left[\mathrm{F e}(\mathrm{C N})_{6}ight]+\mathrm{N} \mathrm{a}_{2} \mathrm{~S} \mathrm{O}_{4}\)
\(\mathrm{N} \mathrm{a}_{4}\left[\mathrm{F} \mathrm{e}(\mathrm{C N})_{6}ight]+\mathrm{F} \mathrm{e}^{+} \mathrm{3} \longrightarrow \mathrm{F} \mathrm{e}_{4}\left[\mathrm{F} \mathrm{e}(\mathrm{C N})_{6}ight]_{3}\)
So, \(\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6} ight]_{3}\) is responsible for prussian blue colour obtained during the test of Nitrogen and Lassaigne test. O-nitrophenal is more volatile than pnitrophenal. There is intramolecular \(\mathrm{H}\) - bonding in \(\mathrm{O}-\) nitrophenal while in \(\mathrm{p}-\) nitrophenal there is intermolecular hydrogen bonding which cause association of molecule. Intermolecular \(\mathrm{H}\) - bondingincrease, boiling point increases while volatility reduces. /

Asked in: JEE-TOPICTESTS-CHEMISTRY

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