Question

Out of starch and ferric hydroxide which can easily be coagulate and why?

Answer 1

To answer we should know about Lyophilic and lyophobic colloids. Both are the type of colloidal based on the interaction between dispersed and dispersion phase. In lyophilic colloids, the dispersed phase has good interaction with the dispersion phase. In lyophobic colloids, the dispersed phase itself does not interact with the dispersion phase.
Complete answer:
A colloid is a heterogeneous mixture in which a phase remains dispersed in the suspension. The size of colloidal particles varies from $10$ to $1000\,{{\text{A}}^ \circ }$. The phase which remains dispersed is known as the dispersed phase. The phase in which the dispersed phase solubilizes is known as the dispersion phase.

On the basis of interaction between the dispersed phase and dispersion phase, the colloids are divided into two parts:
Lyophilic: Lyophilic colloids are liquid loving means dispersed phase easily interacts with the dispersion phase, so they can easily form by mixing. Lyophilic colloids are stable. They do not coagulate, so do not require a stabilizer. The lyophilic colloid can be separated by just evaporation and can again form by remixing, so they are reversible.

Lyophobic: Lyophobic colloids are liquid hater means dispersed phase does not interact easily with the dispersion phase so, they cannot be formed by mixing so, they can be prepared by special methods only. Lyophilic colloids are not stable. They require stabilizers because they coagulate easily. The lyophilic colloid cannot be separated just by evaporation and cannot again form by remixing, so they are irreversible.

Starch is lyophilic colloid whereas ferric hydroxide is a lyophobic colloid. When an electrolyte is mixed with ferric hydroxide, it coagulates easily. Therefore, out of starch and ferric hydroxide, ferric hydroxide can easily be coagulated because it is a lyophobic colloid.

Note: Metal sulphides and hydroxide are the lyophobic colloids that are made by a specific method such as gold sol which is prepared by Bredig’s arc method. Lyophobic colloids are reversible colloids whereas lyophobic colloids are irreversible colloids. Lyophobic colloids are not stable because of heating or shaking they coagulate. When the dispersion phase is water then the lyophilic colloid is known as hydrophilic colloid and the lyophobic colloids are known as hydrophobic colloids.