Question

In an attempt to prepare ferric hydroxide sol by adding small amount of ferric chloride to water, one person got a precipitate of ferric hydroxide. 

a) How can you help him to convert Fe(OH)₃ precipitate to Fe(OH)₃ sol?

b) Name the phenomenon behind this.

c) What happens when BaCI₂ is added to Fe(OH)₃ sol?

d) Give reason forthe above.

Answer 1

a) By adding a solution of FeCI₃ to the fresh precipitate of ferric hydroxide.

b) Peptization

c) Precipitation of Fe(OH)₃ sol will take place.

d) BaCI₂ being an electrolyte ionises to Ba²⁺ + and Cl ions. The particles of Fe(OH)₃ precipitate adsorb Ba²⁺ ions to their surface and get positively charged. These positively charged particles of the precipitate repel each other and ultimately break up into smaller particles of the size of a colloid. Here BaCI₂ is acting as a peptizing agent.