Question

Explain why an aqueous solution of potassium hexacyanoferrate(II) does not give the test for ferrous ions.

Answer 1

Before answering this question, we should know something about Potassium Hexacyanoferrate(II). It is also known as potassium ferrocyanide is an inorganic compound that has a chemical formula of it is ${{K}_{4}}[Fe{{(CN)}_{6}}].3{{H}_{2}}O$.

Complete answer:
Production of Potassium Hexacyanoferrate(II)-
Ferrous Chloride, Calcium hydroxide, and hydrogen cyanide form $C{{a}_{2}}[Fe{{(CN)}_{6}}].11{{H}_{2}}O$, and then it is treated with potassium salts and precipitates the Calcium-potassium salts. Calcium-potassium salts are then treated with Potassium carbonate to give Potassium hexacyanoferrate(II). There are lemon-yellow monoclinic crystals that are formed by the salts.
In the old times, Potassium ferrocyanide was decomposed to produce Potassium cyanide. Potassium ferrocyanide was considered an important source to produce alkali metal cyanides before the castner process was discovered.
Potassium hexacyanoferrate (II) fails to produce ferrous ions ($F{{e}^{2+}}$) in the aqueous solution as it is a complex and the ferrous ions are in the coordination sphere and it bonds with cyanide (Coordinate bonds), CN-ligands.

Note:
Uses of Potassium Hexacyanoferrate (II) are- The usage in road salt and table salt as an anticaking agent. It was authorized as a salt substitute in 2018. It helps to purify the tin and is used to separate Cu from molybdenum ore. It helps to produce citric acid and wine. It can act as a fertilizer too to save plants. Its usage is also in the animal feed. There are laboratory uses as well like to find out the concentration of potassium permanganate, It can also be used in the titration process. It can also be used to identify iron in the labs.