Question

A colloidal solution is subjected to an electrical field. The particles move towards anode. The coagulation of the same sol is studied using NaCl, $BaC{l_2}$ and $AlC{l_3}$ solutions. Their coagulation power should be:
A) $NaCl > BaC{l_2} > AlC{l_3}$
B) $BaC{l_2} > AlC{l_3} > NaCl$
C) $AlC{l_3} > BaC{l_2} > NaCl$
D) $BaC{l_2} > NaCl > AlC{l_3}$

Answer 1

The coagulating power depends on the valency or charge of the ion of the solution i.e., it increases with the increase in valency of the ion. The valency of Aluminium $\left( {Al} \right)$ in aluminium chloride $\left( {AlC{l_3}} \right)$ is 3, Barium $\left( {Ba} \right)$ in barium chloride $\left( {BaC{l_2}} \right)$ is 2 and sodium $\left( {Na} \right)$ in sodium chloride $\left( {NaCl} \right)$ is 1.

Complete step by step answer:
A mixture in which one substance is divided into minute particles and these particles are dispersed throughout a second substance i.e., they are evenly spread throughout the entire solution. These types of solutions are known as colloidal solution. These minute sized particles are known as colloidal particles. The size of the particles present in the solution is larger than those found in true solutions but they are too small to be seen with a microscope.
This solution is subjected to an electrical field and the particles move towards anode i.e., positive electrode. Hardy-Schulze rule states that the ion that causes a solution to coagulate or accumulate is opposite in sign to the electrical charge of the colloidal particle and further the coagulating power increases with the increase in valency of the ion of the solution. A sol is a colloid which is made out of very small solid particles in a liquid medium. So, among the sol NaCl,$BaC{l_2}$ and$AlC{l_3}$ , the coagulation power of $AlC{l_3}$is maximum and it is minimum for NaCl because the valency of Al in $AlC{l_3}$is 3 and Na in NaCl is 1. Hence, the order of coagulation power is $AlC{l_3} > BaC{l_2} > NaCl$.

Hence, the option C is the correct answer.

Note: Remember that the coagulation power of sol depends on the valency of the ions present in the solution i.e., coagulation power increases with the increase in valency of ion and vice-versa and also remember the valency of each elements of these compounds.