Question

Which one of the following statements is FALSE for hydrophilic sols?

• A. They do not require electrolytes for stability.
• B. These sols are reversible in nature.
• C. Their viscosity is of the order of that of H$_2$O.
• D. The sols cannot be easily coagulated.

Hint:

Contrast the properties of hydrophilic vs. hydrophobic (lyophilic vs. lyophobic) sols. Hydrophilic: reversible, highly stable, high viscosity, hard to coagulate. Hydrophobic: irreversible, less stable (needs charge), low viscosity, easy to coagulate with small amounts of electrolyte.

Answer 1

The Correct Option is C

To determine which statement is FALSE for hydrophilic sols, let's analyze each option:

1. They do not require electrolytes for stability.
   • Hydrophilic sols have an affinity for water due to the presence of hydrophilic groups on the surface of colloidal particles. These groups allow the particles to remain stable in water without the need for additional electrolytes. Thus, this statement is TRUE.
2. These sols are reversible in nature.
   • Hydrophilic sols are indeed reversible because they can easily switch between a gel and a sol state when adding or removing the dispersing medium (usually water). Therefore, this statement is TRUE.
3. Their viscosity is of the order of that of H₂O.
   • Hydrophilic sols generally have a higher viscosity compared to pure water due to the interaction between the dispersed particles and the water. Therefore, this statement is FALSE and matches our goal of identifying the incorrect statement.
4. The sols cannot be easily coagulated.
   • Hydrophilic sols resist coagulation unless a sufficient concentration or specific type of electrolyte is added. This is generally true because the particles are stabilized by the solvation effect, thus making the statement TRUE.

Based on the analysis above, the correct answer is: Their viscosity is of the order of that of H₂O. This statement is FALSE because the viscosity of hydrophilic sols is typically higher than that of water.