Question

The ${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$ is used on detecting
A.$F{e^{3 + }}$ ion
B.$C{u^ + }$ ion
C.$C{u^{3 + }}$ ion
D.$F{e^{2 + }}$ ion

Answer 1

${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$ is potassium ferrocyanide. It is a coordination compound. In the compound potassium ferrocyanide, the six cyanide ligands are coordinated bonded with the central metal atom which is iron.

Complete answer:
Potassium ferrocyanide was prepared by reacting prussian blue with potassium carbonate. Industrially, it is produced from hydrogen cyanide, ferrous chloride and calcium hydroxide. The product obtained is reacted with potassium salts in potassium carbonate to give tetra potassium salt.
Potassium ferrocyanide is used to detect $F{e^{3 + }}$ ions. These ions react with potassium ferrocyanide and form ferric ferrocyanide. Ferric ferrocyanide is a blue precipitate. The reaction that takes place is as follows,
$F{e^{3 + }} + {\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }} \to F{e_4}{\left[ {Fe{{\left( {CN} \right)}_6}} \right]_3}$
Hence, potassium ferrocyanide is used in detecting $F{e^{3 + }}$ ions.

Therefore, the correct answer is option A.

Note:
Potassium ferrocyanide is widely used as anti-caking agents for both road salt and table salt. It is also used in the purification of tin. The production of wine and citric acid is done using potassium ferrocyanide. It is also used to determine the concentration of potassium permanganate. As a fertilizer in the plants, potassium ferrocyanide is used.
Ferric ferrocyanide, also known as berlin blue or prussian blue, is a dark blue pigment. It is produced by oxidation of ferrous ferrocyanide salts. Ferric ferrocyanide was the first modern synthetic pigment. Common histopathology stain used by pathologists is prussian blue. Ferric ferrocyanide is present in some preparation of laundry bluing. Ferric ferrocyanide is extremely insoluble but it also tends to form colloids.