Question:
A colloid is formed by adding FeCl3 in excess of hot water. What will happen if excess sodium chloride is added to this colloid?
Solution:
FeCl3 when added into hot water, it forms hydrated ferric oxide, which is a positively charged sol due to absorption of Fe3+ ions. On adding NaCl the negatively charged chloride ions neutralize the positive charge of the solution and coagulation of the sol takes place.