Question

Write the chemical method by which \[Fe{\left( {OH} \right)_3}\] sol is prepared from \[FeC{l_3}\].

Answer 1

Hint:
Most of Metal halides form its hydroxides when treated with compounds that have a displaceable\[^ - OH\] ion. Sol is just a type of a colloidal solution of Solid particles dispersed in Liquid medium.

Complete step-by-step answer:
To make \[Fe{\left( {OH} \right)_3}\] sol from \[FeC{l_3}\] solution, first we need to convert \[FeC{l_3}\] to \[Fe{\left( {OH} \right)_3}\] by adding some reagent.
Now, Water can react with \[FeC{l_3}\] to give \[Fe{\left( {OH} \right)_3}\] at elevated temperatures. The reaction will be called Hydrolysis.
\[FeC{l_3} + 3{H_2}O \to Fe{\left( {OH} \right)_3} + 3HCl\]
So, by boiling this mixture, we get dark brown precipitates of \[Fe{\left( {OH} \right)_3}\]. We get precipitates because the solubility of \[Fe{\left( {OH} \right)_3}\] in water is very low.
 Here, Colloidal solution is still not formed. To make a Sol(a type of Colloid), we need to add more water into it. This results in agglomeration(assembling) of particles. Water needs to be preferentially hot to make solvation easy. Then, a sol is formed. It is called \[Fe{\left( {OH} \right)_3}\] sol.
As we have seen in the reaction, Hydrochloric acid is also produced. It needs to be removed from the reaction mixture otherwise it creates interference in the formation of sol. We can use the Dialysis method for the removal of HCl. So, this was the chemistry behind this reaction. Complete step-by-step procedure to obtain sol from the Ferric chloride solution is as shown below.
- Take a clean conical flask of 250mL.
- Prepare a dilute solution of Ferric chloride of known concentration. \[2 - 10\% W/V\] concentration would be preferred.
- Take 100mL of distilled water in a conical flask and boil it with the help of wire gauze.
- Now, add ferric chloride solution into this flask containing water drop by drop. Use burette to add this solution and make sure that you add only 10mL of that solution. Make sure that the mixture is constantly stirred while adding the solution.
- Heat the solution until you see a deep red or brown coloured solution.
- Then keep the mixture aside and allow it to stand for some time. Then the ferric hydroxide sol will be ready.

Note:
- Here the detailed description of the method is being asked, so don’t just write the name of the method.
- In the reaction boiling of mixture is required in order to obtain product. Also dilution in the end is also necessary as concentrated solution will not end up being a sol.