Which of the following statement is false?

For oil in water emulsions, long chain alcohols acts as emulsifying agents

The correct answer is option 3. For oil in water emulsions, long chain alcohols acts as emulsifying agents.

Let us analyze each statement carefully to identify which one is false, along with a detailed explanation:

1. Refractive index of dispersion phase and dispersion medium should differ in magnitude for Tyndall effect

The Tyndall effect is the scattering of light by colloidal particles when a beam of light passes through a colloidal solution. This effect is visible when the particles are large enough to scatter light. However, for the Tyndall effect to occur, there must be a difference in the refractive indices of the dispersed phase (the colloidal particles) and the dispersion medium (the liquid or gas in which particles are dispersed). If their refractive indices are similar, light will not scatter, and the Tyndall effect will not be observed.

Example: In colloidal solutions like milk, the Tyndall effect is observed because the refractive indices of fat globules (dispersed phase) and water (dispersion medium) are different.

Conclusion: This statement is true because the difference in refractive indices is necessary for the Tyndall effect to be seen.

2. Electrophoresis shown by lyophobic colloids is mainly due to preferentially absorbed ions

Lyophobic colloids (such as metal sols) exhibit electrophoresis, which is the movement of colloidal particles under an electric field. This happens because the colloidal particles acquire a charge due to the adsorption of ions from the surrounding medium onto their surface. These ions give the colloidal particles a net charge, which causes them to move toward the oppositely charged electrode when an electric field is applied. The charge on these particles is primarily due to preferential adsorption of ions onto their surface, which leads to the electrophoretic movement.

Example: A silver sol (Ag colloidal solution) can show electrophoresis because the silver particles adsorb certain ions (such as \( Ag^+ \) or \( OH^- \)) from the solution.

Conclusion: This statement is true because electrophoresis occurs due to the charge imparted by preferentially adsorbed ions.

3. For oil in water emulsions, long-chain alcohols act as emulsifying agents

An emulsion is a mixture of two immiscible liquids, where one liquid (dispersed phase) is dispersed in the other (continuous phase). There are two types of emulsions:

Oil-in-water (O/W) emulsions: Oil droplets are dispersed in water.

Water-in-oil (W/O) emulsions: Water droplets are dispersed in oil.

Emulsifying agents help stabilize emulsions by reducing surface tension between the two immiscible liquids. For oil-in-water emulsions, common emulsifying agents are soaps, detergents, and proteins, which have hydrophilic (water-attracting) and hydrophobic (water-repelling) parts, allowing them to stabilize oil droplets in water.

Long-chain alcohols are not typically used as emulsifying agents for oil-in-water emulsions. They are more commonly used as stabilizers for water-in-oil emulsions, where they help stabilize water droplets in oil by forming a protective layer around the water droplets. In oil-in-water emulsions, the role of emulsifiers is better performed by surfactants like sodium stearate or proteins.

Conclusion: This statement is false because long-chain alcohols are generally used in water-in-oil emulsions, not oil-in-water emulsions.

4. Lamp black acts as an emulsifying agent for water in oil emulsions

Lamp black is a form of finely divided carbon, often used in water-in-oil emulsions. It acts as an emulsifying agent by stabilizing the dispersed water droplets in the continuous oil phase. In water-in-oil emulsions, the water is the dispersed phase, and the oil is the continuous phase, and lamp black helps in creating this stable dispersion by forming a physical barrier around the water droplets.

Example: Lamp black is often used in greases, which are a type of water-in-oil emulsion.

Conclusion: This statement is true because lamp black can act as an emulsifying agent for water-in-oil emulsions.

The false statement is option 3: For oil in water emulsions, long-chain alcohols act as emulsifying agents. This is because long-chain alcohols are primarily used as stabilizers in water-in-oil emulsions, not oil-in-water emulsions.