Surface Chemistry Test - 30

Emulsifying agents are the substances which are soluble in both dispersed medium as well as in the dispersed phase, thereby stabilizing the emulsion. Hence, emulsifying agents are used for the stabilization of the emulsion.

In case of physical adsorption, there is desorption when temperature increases.
Physical adsorption is exothermic in nature. Hence, it is observed at low temperature. it involves weak  van der Waals forces that break at high temperature causing desorption.

The principal emulsifying agent for w/o emulsion is Lampblack or soot. Other emulsifying agents are the heavy metal salts of the fatty acids, long-chain alcohols, etc.

The emulsifying agent used in oil in water emulsion is protein. Milk is an example of oil in water emulsion. It consists of liquid fat dispersed in water. Milk proteins act as an emulsifying agent.

The polar water-soluble ( hydrophilic) head is on the surface of the micelle whereas non-polar oil soluble (hydrophobic) tail is in the centre of the micelle. In the centre of a micelle, small oil droplets are present in which hydrophobic part of micelle dissolves. This results in the formation of oil in water type emulsion.

Peptisation is the process in which freshly prepared precipitate disintegrates into a colloidal solution using suitable electrolyte.

The following is true when soap or detergent is added to water.
The anions of emulsion repel each other hence do not precipitate. Since they have the same charge, there is an electrostatic force of repulsion between like charges. So they do not come closer and cannot coagulate.

Milk is an emulsion in which milk fat is dispersed in water. Emulsions are colloids in which both dispersed phase and dispersion medium are liquids. So, milk is an emulsion in which liquid is dispersed in water.

Correct Option: $$D$$

Hint: Physical adsorption is accompanied by weak van der wal forces

Explanation:

• Physical adsorption is suitable at low temperatures as it is an exothermic
• A process is in accordance with Le Chatlier’s principle so with the increase of temperature the extent of adsorption increases.
• Due to the interaction between adsorbate and adsorbent, the adsorption process becomes exothermic.
• Also, as pressure increases the rate of adsorption increases.
• Gases having higher critical temperatures are easily liquifiable and readily adsorb.

Hint: Gas particles adsorbed on a solid is physisorption

Correct Answer: Option D

Explanation: 

The extent of adsorption of a gas on solid depends on following factors;

1. The nature of the gas: Easily liquefiable gases are readily adsorbed than gases that do not liquefy easily.

2. Pressure of the gas: With increase in pressure, the extent of adsorption increases.

3. Temperature of the gas: Increase in temperature will decrease the extent of adsorption as adsorption is exothermic process.

4. Nature and surface area of the adsorbent: Greater is the surface area of the adsorbent, greater is the extent of adsorption.

Final Answer: The correct answer is all of these, option $$D$$.