Question

When iron hydroxide colloidal sol which is positively charged, and colloidal gold which is negatively charged are mixed, which of the following observation is correct?

• A. There is no effect of mixing the sols
• B. Coagulation in both sols can be brought about
• C. Ferric hydroxide is coagulated
• D. Gold sol is coagulated

Answer 1

The correct option is B Coagulation in both sols can be brought about

When an excess of an electrolyte is added, the colloidal particles are precipitated. The reason is that colloids interact with ions carrying charge opposite to that present on themselves.
This causes neutralisation leading to their coagulation. The ion responsible for neutralisation of charge on the particles is called the coagulating ion. A negative ion causes the precipitation of positively charged sol and vice versa.
So, when iron hydroxide colloidal sol being positive charged is mixed with colloidal gold which is negatively charged brings about the coagulation in both of the sols.
Hence, option $B$ is the right answer.