CBSE Questions for Class 12 Engineering Chemistry Surface Chemistry Quiz 8 - MCQExams.com

A process of converting a precipitate into colloidal sol called Peptization by shaking it with the dispersion medium.

Colloidal solutions of the hydroxides of Fe, Cr, Al etc can be prepared by hydrolysis of their salts

In ultrasonic dispersion, ultrasonic waves are passed through the solution containing larger particles. They break down to form the colloidal solution.

The process of settling of colloidal particles is called coagulation

Explanation:

• Adsorption is the phenomenon in which one substance accumulates on the surface of the other substance.
• The surface on which adsorption takes place is adsorbent.
• The substances which accumulate on adsorbents are adsorbates.

Hence, the correct answer is option $$A$$.

The more the liquifiable nature of the gas, the more is the enthalpy of physisorption. Here water is most liquifiable. So maximum value of enthalpy is of water here.

Adsorption leads to a decrease in the residual forces on the surface of the adsorbent. This causes a decrease in the surface energy of the adsorbent. Therefore, adsorption is always exothermic and $$ \Delta H$$ is negative.

And for reaction to occur $$ \Delta G$$ should be negative so by equation $$\Delta G = \Delta H- T\Delta S $$, $$ \Delta S$$ should be negative.

• Substances, which accelerate the rate of a chemical reaction and themselves remain chemically and quantitatively unchanged after the reaction, are known as catalysts.
  
• Promoters are substances that enhance the activity of a catalyst while poisons decrease the activity of a catalyst.
• In Haber’s process for manufacture of ammonia, molybdenum acts as a promoter for iron which is used as a catalyst.

• If the accumulation of gas on the surface of a solid occurs on account of weak van der Waals’ forces, the adsorption is termed as physical adsorption or physisorption.
  

• Physical adsorption of a gas by a solid is generally reversible. We can say by Le-Chatelier's principle that more of gas is adsorbed when pressure is increased as the volume of the gas decreases and since the adsorption process is exothermic, the physical adsorption occurs readily at low temperature and decreases with increasing temperature.
  
• So the correct case is when it is Low temperature and high pressure the Physisorption tends to happen.
  

• The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed adsorption.
  

• In adsorption, the substance is concentrated only at the surface and does not penetrate through the surface to the bulk of the adsorbent, while in absorption, the substance is uniformly distributed throughout the bulk of the solid or absorbent.
  

• A distinction can be made between absorption and adsorption by taking an example of water vapour. Water vapours are absorbed by anhydrous calcium chloride but adsorbed by silica gel.
  

• Gas mask generally consists of activated charcoal or mixture of adsorbents is usually used for breathing in coal mines.
  
• Activated charcoal acts as adsorbent which adsorbs other gases on its surface. In Gas masks, they adsorb poisonous gases and hence prevent various occupational hazards.

• A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
  

• The essential difference between a solution and a colloid is that of particle size. While in a solution, the constituent particles are ions or small molecules. In a colloid, the dispersed phase may consist of particles of a single macromolecule (such as protein or a synthetic polymer) or an aggregate of many atoms, ions or molecules. 
  

• Gas-gas colloidal system is not possible as we can't distinguish between the dispersed phase and dispersed medium.

• The reactants in gaseous state or in solutions, are adsorbed on the surface of the solid catalyst. The increase in concentration of the reactants on the surface increases the rate of reaction. Adsorption being an exothermic process, the heat of adsorption is utilised in enhancing the rate of the reaction.
  

• A colloidal system in which liquid is a dispersed phase and solid is dispersion medium is known as Gel. Example-Cheese, jellies.
  

• Demulsification is the breaking of a crude oil emulsion into oil and water phases. 
  
• Demulsification is used to separate various mixtures like water in oil and oil in water etc.
• It completely separates the constituent liquids and hence is the reverse of emulsification.

The adsorption of positively charged Fe3+ ions by the sol of hydrated ferric oxide results in positively charged colloid.

• A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
  
• Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $$SnCl_2$$, formaldehyde, phenylhydrazine.
  

• Peptization may be defined as the process of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of a small amount of electrolyte.
  
• The electrolyte used for this purpose is called a peptizing agent.
  
• When a small quantity of $$FeCl_3$$ solution is added to fresh precipitate of $$Fe(OH)_3$$ the precipitate is converted into colloidal sol, which is nothing but the process of peptization.

Hydrophillic colloid particles are attracted toward water. They are also called reversible sols.

Aerosol contains small particles of liquid or solid dispersed in a gas.

These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water. They are also called irreversible sols.

Soap is an excellent cleanser because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid.

A micelle or micella is an aggregate of surfactant molecules dispersed in a liquid colloid.

This observation of Hardy and Schulze are known as Hardy Schulze law. It can be defined as: Greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation. 

• When the reactants, products and the catalyst are in the same phase (i.e., liquid or gas), the process is said to be homogeneous catalysis.
  
• In Heterogeneous catalysis, the reactants, products, and catalyst are in different phase. It is a process occurring at the interface.
• Corrosion and crystallization are the processes which occur at the interface of phases.
• Hence, option C is the right answer.