Question

For coagulation of arsenious sulphide solution, which one of the following salt solutions will be most effective?
(A)$AlC{{l}_{3}}$
(B) NaCl
(C)$BaC{{l}_{2}}$
(D)$N{{a}_{3}}P{{O}_{4}}$

Answer 1

Hint: Coagulation of ions is governed by the coulomb forces. Arsenious sulphide solutions have sulphide ions in the solution, the formula of sulphide ions is ${{S}^{-2}}$. Due to this, the colloidal solution acquires negative charge, which attracts positive charge during coagulation.

Complete step by step answer:
Coagulation is the destabilization of colloids by neutralizing the electric charge of the dispersed phase particles, which result in aggregation of the colloidal particles. Aggregation is a formation of groups of particles bonded to each other by Van der waals or other intermolecular forces. If two solutions of opposite charges are mixed together, their charges are mutually neutralized and both solutions get coagulated.
During coagulation of colloids, there is formation of an electric double layer. This double layer is formed due to the attraction of opposite charges. The first layer, the surface charge, consists of ions adsorbed onto the object due to the chemical interactions. The second layer is composed of ions attracted to the surface charge via the coulomb force, electrically screening the first layer. This second layer is loosely associated with the object.
Since, coagulation is due to the coulomb forces, and coulomb forces depend mainly on the charge of the ions, we will look which of the option has the maximum charge, so that maximum coagulation can occur. Arsenious sulphide solution consists of sulphide ions that have negative charge. Therefore, the option with maximum positive charge will give maximum coagulation.
Option A has $AlC{{l}_{3}}$, it has aluminium cation with +3 charges, and the rest of the options have cations of +1 and +2 charge. Since aluminium cations have the maximum charge, it will give maximum coagulation.
So, the correct answer is “Option A”.

Note: Aggregation is a formation of groups of particles bonded to each other by Van der waals or other intermolecular forces. If two solutions of opposite charges are mixed together, their charges are mutually neutralized and both solutions get coagulated.