Question

Why is ferric hydroxide colloid positively charged when prepared by adding ferric chloride to hot water?
A) Due to precipitation of ferric hydroxide there is an excess of $F{e^{3 + }}$ ions.
B) Due to preferential adsorption of $F{e^{3 + }}$ ions by the sol of $Fe{(OH)_3}$
C) Due to absence of any negatively charged ion.
D) Due to adsorption of $O{H^ - }$ and $C{l^ - }$ions, the remaining sol has only $F{e^{ + 3}}$ ions.

Answer 1

Hint:The colloid can be described as a phase-separated mixture in which one substance is microscopically dispersed particle suspended throughout another substance. So one can apply this concept for the colloid of ferric hydroxide which is positively charged and find relevant options.

Complete step by step answer:1) First of all let us learn about the colloid of ferric hydroxide which is prepared by adding ferric chloride to hot water where the ferric chloride gets hydrated by the excess amount of water and forms the sol of $Fe{(OH)_3}$ from the ferric chloride i.e. $FeC{l_3}$.
2) Now that the $F{e^{3 + }}$ ions formed are also present in an excess amount which are also common to lattice or surface of the sol $Fe{(OH)_3}$
3) Therefore, the $F{e^{3 + }}$ ions formed which are positively charged get adsorbed on the surface of sol that gives the overall charge of the sol as a positive charge.
4) Hence, now we can say that due to preferential adsorption of $F{e^{3 + }}$ ions by the sol of $Fe{(OH)_3}$ ferric hydroxide colloid positively charged when prepared by adding ferric chloride to hot water which shows the option B as a correct choice.



Note: The colloids term includes sols, emulsions, and gels as its constituents. The colloidal particles do not settle in the solution and also they cannot be separated out by using ordinary methods such as filtering or centrifuging. Milk is an example of a colloid in which the butterfat globules are dispersed within a water-based solution. The sol term stands for the solid particle colloids which in the above question are of $Fe{(OH)_3}$ particles.