Question

Addition of $FeC{l}_3$ to $K_{4}Fe(CN{)}_6$ in dilute and cold solution gives:

• A. prussian blue sol
• B. $F{e}_4\left[Fe\right(CN{)}_6{]}_3$ sol
• C. positive sol
• D. All of the above

Answer 1

The correct option is D All of the above

Addition of $FeC{l}_3$ to $K_{4}Fe(CN{)}_6$ in dilute and cold solution gives a positive solution, prussian blue solution and $K\left[Fe\right(Fe\left(CN{)}_6\right)]$

The reaction is as follows:

$4FeC{l}_3+3K_4\left[Fe\right(CN{)}_6]\to F{e}_4[Fe(CN{)}_6{]}_3+12KCl$

If potassium hexacyanoferrate (II) (i.e. potassium ferrocyanide) is added in excess then a product of composition $KFe\left[Fe\right(CN{)}_6]$ is formed which is a positive sol. This tends to form a colloidal solution (‘soluble Prussian blue’) and cannot be filtered.

$FeC{l}_3+K_4\left[Fe\right(CN{)}_6]\to \underset{\text{soluble prussian blue}}{KFe\left[Fe\right(CN{)}_6]}+3KCl$