Question

Addition of $$FeC{l}_3$$ ​to $$K_{4}Fe{\left(CN\right)}_6$$​ in dilute and cold solution gives:
A) Prussian blue sol
B) $$F{e}_4{\left[Fe{\left(CN\right)}_6\right]}_3$$​ sol
C) Positive sol
D) All of the above

Answer 1

Hint: $$FeC{l}_3$$ reacts with $$K_{4}Fe{\left(CN\right)}_6$$ to form a compound having pigmented property and forms a coordination compound having iron as central atom and the cyanide as neutral ligand. In this compound iron has the oxidation state of +3.

Complete step by step answer:
Addition reaction of $$FeC{l}_3$$to $$K_{4}Fe{\left(CN\right)}_6$$ is as follows:
$$4FeC{l}_3+3K_{4}Fe{\left(CN\right)}_6\to F{e}_4{\left[Fe{\left(CN\right)}_6\right]}_3+12KCl$$​
If potassium Ferrocyanide is added in excess then it leads to formation of $$KFe\left[Fe{\left(CN\right)}_6\right]$$ which is a positive sol. The formed product is a form of colloidal solution (‘soluble Prussian blue’) and cannot be filtered and is precipitated down.
$$4FeC{l}_3+3K_{4}Fe{\left(CN\right)}_6\to \underset{\text{soluble prussian blue}}{KFe[Fe{(CN)}_6]}+3KCl$$
Addition of $$FeC{l}_3$$to $$K_{4}Fe{\left(CN\right)}_6$$​ in dilute and cold solution gives a positive solution of $$F{e}_4{\left[Fe{\left(CN\right)}_6\right]}_3$$, and if $$K_{4}Fe{\left(CN\right)}_6$$is added in excess then it leads to formation of $$K\left[Fe\left(Fe{\left(CN\right)}_6\right)\right]$$ which is a Prussian blue ppt.

Therefore, the correct option is D.

Additional information:
Prussian blue is a dark blue pigment which is produced by oxidation of salts of ferrous to Ferric cyanide salts. It has an identical chemical compound Turnbull's blue which is chemically identical to it, but is made up of different reagents,
It was the first known modern pigment synthetically produced. It is not soluble in water thus it is prepared from colloidal dispersion. It includes a variety of ions and the texture of the pigment is because of the colloidal particle sizes.
Properties:
It is a powdered compound. Which is blue in colour.
Insoluble in water.
It forms colloids.
It is complex structurally.

Note: Iron chloride is another name given to Ferric chloride which is a chemical compound having chemical formula of $$FeC{l}_3$$. It has a relatively low melting point, and its boiling point for iron chloride is around 315.C. In addition to water it undergoes hydration reaction and produces heat as a result of exothermic reaction. It is produced industrially by the reaction between dry chlorine with the scrap iron at temperatures of 500 to 700 degrees Celsius.