Question

What would be the correct increasing order of the coagulating power of electrolytes having ions $N{a^ + },A{l^{3 + }}$ and $B{a^{2 + }}$ for arsenic sulphide solution?
A) $B{a^{2 + }} < N{a^ + } < A{l^{3 + }}$
B) $A{l^{3 + }} < N{a^ + } < B{a^{2 + }}$
C) $A{l^{3 + }} < B{a^{2 + }} < N{a^ + }$
D) $N{a^ + } < B{a^{2 + }} < A{l^{3 + }}$

Answer 1

As we know that coagulating power of electrolytes is basically the minimum strength of flocculation where ions which carry the opposite charge to that of the charge compared to the particles of solution responsible for the coagulation of the solution thus following the Hardy-Schulze law.

Complete solution:
As we know that coagulating power of electrolytes is basically the minimum strength of flocculation where ions carry the opposite charge to that of the charge compared to the particles of solution responsible for the coagulation of the solution. Also we know that the precipitation capacity of different electrolytes depends upon the valency of the active or flocculating ions carrying the opposite charge when compared to the charge on colloidal particles.
We also know that according to the Hardy-Schulze principle the increase in valency of the active ion increases it’s coagulating or precipitating power and the coagulation power is directly proportional to the fourth power of the active ions.
Therefore, from the above explanation we can say that the coagulating power of the negative solution of Arsenic sulphide will depend upon the precipitation power of cations which is directly related to its valency, hence it will be found in the increasing order as $N{a^ + } < B{a^{2 + }} < A{l^{3 + }}$.

Therefore,the correct option B.

Note: Remember that when two oppositely charged solutions are mixed in equimolar concentrations, they tend to neutralise the charge of each other and both get coagulated. Also the smaller the size of an ion, larger will be the polarising power of that ion and greater the charge on an ion, higher will be the coagulation power of that ion.