Question

For coagulation of arsenious sulphide sol, which one of the following salt solutions will be most effective?
1. BaCl₂
2. AlCl₃
3. Na₃PO₄
4. NaCl

Answer 1

Correct Answer - Option 2 : AlCl₃

Concept:

For coagulation of a negatively charged arsenious sulphide sol, the cation which is in higher oxidation state will be the most effective. Arsenious sulphide sol is a negative colloid. So, it will be coagulated by the cation of an electrolyte.

As arsenious sulphide is negatively charged, it is easily coagulated by positively charged electrolyte
from the given option, AlCl₃s has +3 charge, and it’s more suitable for coagulation. According to the Hardy-Schulza rule, the higher the charge of the ion, the more effective it is in bringing about coagulation. Here the cations available are Al³⁺ from AlCl₃, Ba²⁺ from BaCl₂ and Na⁺ from Na3PO4 and NaCl. So, their power to coagulate As₂ S₃ (Arsenic trisulfide) will follow the order Al³⁺ > Ba²⁺ > Na⁺