Question

The dispersed phase in colloidal iron (III) hydroxide and colloidal gold is positively and negatively charged respectively. Which of the following statements is not correct?
A.Magnesium Chloride solution coagulates gold sol readily than iron (III) hydroxide sol.
B.Sodium sulphate solution causes coagulation in both sols.
C.Mixing of two sols has no effect.
D.Coagulation in both sols can be brought about by electrophoresis.

Answer 1

Hint: Coagulation is a chemical process for removing particles in suspended or colloidal form. These particles do not settle on standing. Also, these particles cannot be removed by conventional physical treatment processes.

Complete step by step answer:
We know a negatively charged gold solution is coagulated by a Magnesium Chloride solution readily than positively charged iron (III) hydroxide solution. Also, in Magnesium chloride, the charge on cation is twice the charge on the anion. Higher is the charge on ion, higher will be its coagulating power.

Also we have studied that Sodium sulphate solution causes coagulation in both solutions. Negatively charged gold sol is coagulated by sodium ions and positively charged iron (III) hydroxide sol is coagulated by sulphate ions.

The dispersed phase in colloidal gold and colloidal iron (III) hydroxide is negatively and positively charged respectively. Mutual Coagulation is affected when two solutions are mixed.. This is due to neutralization of the charge on one sol by opposite charge on another sol.

By electrophoresis, coagulation in both the solutions can be brought. We know that, during electrophoresis, through the colloidal solution an electric current is passed and the experiment is arranged in such a manner that only particles can move.
After studying above points, we can conclude that option A, B and D are correct and C is incorrect.

So, the correct option is C, i.e. mixing of two sols has no effect.

Note:
Coagulation is a process used to neutralize charges and form a gelatinous mass to trap (or bridge) particles thus forming a mass large enough to settle or be trapped in the filter. Always remember that coagulation only takes place when two oppositely charged sols are mixed together. Higher the valency of ion, higher will be its coagulating power.