Question

The properties of solutions containing surface active agents change sharply over a narrow concentration range and are called as

• A. Critical micelle concentration
• B. Ionic concentration
• C. Hydrogen ion concentration
• D. Surface tension

Answer 1

The Correct Option is A

The question asks about the concentration range over which the properties of solutions containing surface-active agents change sharply. Let's examine the options to identify the correct one:

1. Critical Micelle Concentration (CMC): Surface-active agents, also known as surfactants, are compounds that lower the surface tension between two liquids or between a liquid and a solid. At low concentrations, surfactant molecules exist as individual molecules. However, as the concentration increases, there is a point where these molecules begin to aggregate into structures known as micelles. This point is known as the Critical Micelle Concentration (CMC). Beyond this concentration, any additional surfactant molecules form micelles, which significantly changes the properties of the solution. Thus, the properties change sharply over this narrow concentration range.
2. Ionic Concentration: While ionic concentration is crucial in solutions, it does not relate specifically to surface-active agents in terms of altering their properties like micelle formation.
3. Hydrogen Ion Concentration: This usually pertains to the acidity or basicity (pH level) of a solution and is not directly related to the behavior of surfactants.
4. Surface Tension: Surface tension refers to the tendency of liquid surfaces to shrink into the minimum surface area possible. Surfactants indeed reduce surface tension, but the question focuses on a concentration range, which is best described by CMC.

Based on the details above, the correct answer is Critical Micelle Concentration. This is because at the CMC, the formation of micelles begins, and the properties of the solution change significantly, marking a sharp transition which is characteristic of solutions containing surfactants.