Question

The disperse phase in colloidal iron (III) hydroxide and colloidal gold is positively and negatively charged respectively. Which of the following is/are not correct?

• A. Magnesium chloride solution coagulates the gold solution more readily than iron (III) hydroxide solution.
• B. Sodium sulphate solution cause coagulation in both solutions.
• C. Mixing of the solutions has no effect.
• D. Coagulation in both solutions can be brought about by electrophoresis.

Answer 1

The correct option is C Mixing of the solutions has no effect.

As dispersed phase in colloidal iron (III) hydroxide is positively charged, it can be coagulated by negative ions.

Dispersed phase in colloidal gold sol is negatively charged, it can be coagulated by positive ions.

In Mg chloride, positive cation $M{g}^{+2}$ coagulates iron (III) hydroxide and $C{l}^{-}$ ion coagulates colloidal gold sol. As cation has more charge than anion, it coagulates fast.

Also, sodium sulphate solution contains both cation and anion. So, it can coagulate both sols.

Coagulation in both sols can be brought about by electrophoresis.

But when we mix them together, due to opposite charge colloidal sol they coagulate.