Textbook Question
A series of anions is shown below: The anion on the far right is called 'BARF' by chemists, as its common abbreviation sounds similar to this word. (c) Which, if any, of these anions has an expanded octet around its central atom?
Ch.13 - Properties of Solutions
Chapter 13, Problem 114a
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 guidance1
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.
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.
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.
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.
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.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
1mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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.
Recommended video:
Guided course
07:35
Calculate Concentration of the Basic Form
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.
Recommended video:
Guided course
00:57Speed of Light Formula
Related Practice
Textbook Question
A small cube of lithium 1density = 0.535 g/cm32 measuring 1.0 mm on each edge is added to 0.500 L of water. The following reaction occurs: 2 Li1s2 + 2 H2O1l2 ¡ 2 LiOH1aq2 + H21g2 What is the freezing point of the resulting solution, assuming that the reaction goes to completion?
Textbook Question
What is the boiling point of a 0.10 M solution of NaHSO4 if the solution has a density of 1.002 g>mL?
1
views