Compounds like sodium stearate, called 'surfactants' in general, can form structures known as micelles in water, once the solution concentration reaches the value known as the critical micelle concentration (cmc). Micelles contain dozens to hundreds of molecules. The cmc depends on the substance, the solvent, and the temperature. (a) The turbidity (the amount of light scattering) of solutions increases dramatically at the cmc. Suggest an explanation. .

Verified step by step guidance

1. Understand the concept of micelles: Micelles are spherical aggregates of surfactant molecules in a liquid colloid, where the hydrophobic tails are in the interior and the hydrophilic heads are on the exterior, interacting with water.
2. Recognize the role of critical micelle concentration (cmc): The cmc is the concentration of surfactants above which micelles form and below which only individual surfactant molecules are present.
3. Consider the effect of micelle formation on light scattering: When micelles form, they create larger structures compared to individual surfactant molecules, which can scatter light more effectively.
4. Relate turbidity to light scattering: Turbidity is a measure of the cloudiness or haziness of a fluid, which is directly related to the amount of light scattered by particles in the solution.
5. Conclude that the increase in turbidity at the cmc is due to the formation of micelles, which scatter light more than individual surfactant molecules, leading to a dramatic increase in turbidity.

Key Concepts

Surfactants

Surfactants are compounds that lower the surface tension between two substances, such as oil and water. They have a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail, allowing them to interact with both polar and nonpolar substances. This unique structure enables surfactants to aggregate in water, forming micelles when the concentration exceeds the critical micelle concentration (cmc).

Critical Micelle Concentration (cmc)

The critical micelle concentration (cmc) is the specific concentration of surfactants in a solution at which micelles begin to form. Below this concentration, surfactant molecules exist primarily as individual entities, while above it, they aggregate into micelles. The cmc is influenced by factors such as the type of surfactant, the solvent used, and the temperature of the solution.

Turbidity and Light Scattering

Turbidity refers to the cloudiness or haziness of a solution caused by the presence of suspended particles. In the context of micelle formation, as surfactants reach the cmc and aggregate into micelles, they scatter light more effectively due to their size and structure. This increase in light scattering results in a noticeable rise in turbidity, indicating the transition from individual surfactant molecules to organized micellar structures.