Question

Which of the following will show Tyndall effect? (a) Aqueous solution of soap above critical micelle concentration (b) Aqueous solution of soap below critical micelle concentration (c) Aqueous solution of sugar (d) Aqueous solution of sodium chloride

Short answer

(a) Aqueous solution of soap above critical micelle concentration shows the Tyndall effect.

Step-by-step solution

Understanding the Tyndall Effect

The Tyndall effect is the scattering of light by particles in a colloid or very fine suspension. It is observed in colloidal solutions because the particle size is large enough to scatter light, making the light path visible.

Examining Aqueous Soap Solution Above Critical Micelle Concentration

Above the critical micelle concentration (CMC), soap molecules form micelles, which are aggregates of molecules that stabilize as colloidal particles. Hence, the solution can scatter light and will show the Tyndall effect.

Examining Aqueous Soap Solution Below Critical Micelle Concentration

Below the critical micelle concentration, soap molecules are dispersed as individual ions or molecules, not aggregate colloidal particles. Therefore, the solution does not feature large enough particles to scatter light effectively, hence will not show the Tyndall effect.

Testing Sugar Solution

Sugar solution consists of dissolved sugar molecules which are too small to act as colloidal particles. Therefore, aqueous sugar solutions cannot scatter light in a way necessary to exhibit the Tyndall effect.

Testing Sodium Chloride Solution

Similar to sugar, an aqueous sodium chloride solution contains dissolved ions that are too small to scatter light. Hence, it does not demonstrate the Tyndall effect.

Key concepts

Critical Micelle Concentration

In simple terms, the **Critical Micelle Concentration (CMC)** is the point where soap molecules begin to cluster together in water to form structures called micelles. These micelles are tiny, spherical structures where the soap molecules are arranged in such a way that their tails are hidden from the water. This formation is crucial because it marks the transition from individual soap molecules to those aggregating in larger entities.

When the concentration of soap in water is below the CMC, the soap molecules are just floating around separately. Conversely, when the concentration exceeds the CMC, these dispersed molecules come together in micelles.

• Below CMC: **Individual molecules** in the solution.
• Above CMC: Formation of **micelles** with i.e., colloidal properties.

Learning about CMC is important because it helps to understand when a solution becomes capable of scattering light, like in the case of the Tyndall effect.

Colloids

Colloids are fascinating because they are mixtures where one substance is dispersed evenly throughout another. What's intriguing about them is the size of their particles. These particles are larger than those found in solutions but smaller than those in suspensions. This middle-ground size makes them unique in behavior and characteristics.

Colloidal solutions can be a lot of things: aerosols like fog, gels like jelly, or emulsions like mayonnaise. One typical property is that they'll scatter light, demonstrating the Tyndall effect. This happens because the particles in a colloidal system, like those in a soap solution above its CMC, are just the right size to interact with light in this special way.

• Large enough particles to **scatter light**.
• Common examples: **fog**, **smoke**, emulsions.

Understanding colloids help explain various everyday phenomena and various industrial applications.

Light Scattering

**Light scattering** is an occurrence that we observe almost daily, consciously or not. It happens when small particles or colloidal matter deflect the course of light waves passing through them, which can result in visible rays of light. In nature, this is why we see sunbeams in a dust-filled room or the blue color of the sky.

In scientific terms, when light hits small particles, instead of continuing in a straight line, it bounces off or scatters in different directions. The Tyndall effect is a perfect showcase of this principle, where light is scattered by particles in a colloid. Remember that:

• The size of the particles dictates their **ability to scatter light.**
• For small particles like molecules in sugar water, effective scattering doesn't occur, so they remain invisible under direct light.

This principle is also leveraged in various technological and industrial processes, including the design of optical instruments.