(i) On thebasis of the physical state of the components (by components we mean thedispersed phase and dispersion medium). Depending on whether the components aresolids, liquids, or gases, we can have eight types of colloids.

(ii) On thebasis of the dispersion medium, sols can be divided as:

Dispersion medium	Name of sol
Water	Aquasol or hydrosol
Alcohol	Alcosol
Benzene	Benzosol
Gases	Aerosol

(iii) Onthe basis of the nature of the interaction between the dispersed phase anddispersion medium, the colloids can be classified as lyophilic (solventattracting) and lyophobic (solvent repelling).

Question - 22 : -
Explain what is observed

Answer - 22 : -

(i) When a beam of light is passed through a colloidal sol.

(ii) An electrolyte, NaCl is added to hydrated ferric oxide sol.

(iii) Electric current is passed through a colloidal sol?

Answer

(i) When abeam of light is passed through a colloidal solution, then scattering of lightis observed. This is known as the Tyndall effect. This scattering of lightilluminates the path of the beam in the colloidal solution.

(ii) When NaClis added to ferric oxide sol, it dissociates to give Na⁺ and Cl^-ions. Particles of ferric oxide sol are positively charged. Thus, they getcoagulated in the presence of negatively charged Cl^- ions.

(iii) Thecolloidal particles are charged and carry either a positive or negative charge.The dispersion medium carries an equal and opposite charge. This makes thewhole system neutral. Under the influence of an electric current, the colloidalparticles move towards the oppositely charged electrode. When they come incontact with the electrode, they lose their charge and coagulate.

Question - 23 : -
What are emulsions? What aretheir different types? Give example of each type.

Answer - 23 : -

The colloidal solution in whichboth the dispersed phase and dispersion medium are liquids is called anemulsion.

There are two types of emulsions:

(a) Oil in water type:

Here, oil is the dispersed phasewhile water is the dispersion medium. For example: milk, vanishing cream, etc.

(b) Water in oil type:

Here, water is the dispersedphase while oil is the dispersion medium. For example: cold cream, butter, etc.

Question - 24 : -
What is demulsification? Name twodemulsifiers.

Answer - 24 : -

The process of decomposition ofan emulsion into its constituent liquids is called demulsification. Examples ofdemulsifiers are surfactants, ethylene oxide, etc.

Question - 25 : -
Action of soap is due toemulsification and micelle formation. Comment.

Answer - 25 : -

The cleansing action of soap isdue to emulsification and micelle formation. Soaps are basically sodium andpotassium salts of long chain fatty acids, R-COO^-Na⁺. Theend of the molecule to which the sodium is attached is polar in nature, whilethe alkyl-end is non-polar. Thus, a soap molecule contains a hydrophilic(polar) and a hydrophobic (non-polar) part.

Whensoap is added to water containing dirt, the soap molecules surround the dirtparticles in such a manner that their hydrophobic parts get attached to thedirt molecule and the hydrophilic parts point away from the dirt molecule. Thisis known as micelle formation. Thus, we can say that the polar group dissolvesin water while the non-polar group dissolves in the dirt particle. Now, asthese micelles are negatively charged, they do not coalesce and a stable emulsionis formed.

Question - 26 : -
Give four examples ofheterogeneous catalysis.

Answer - 26 : -

(i) Oxidationof sulphur dioxide to form sulphur trioxide. In this reaction, Pt acts as acatalyst.

(ii) Formationof ammonia by the combination of dinitrogen and dihydrogen in the presence offinely divided iron.

This process is called theHaber’s process.

(iii) Oswald’sprocess: Oxidation of ammonia to nitric oxide in the presence of platinum.

(iv) Hydrogenationof vegetable oils in the presence of Ni.

Question - 27 : -
What do you mean by activity andselectivity of catalysts?

Answer - 27 : -

(a) Activity of acatalyst:

The activity of a catalyst is itsability to increase the rate of a particular reaction. Chemisorption is themain factor in deciding the activity of a catalyst. The adsorption of reactantson the catalyst surface should be neither too strong nor too weak. It shouldjust be strong enough to make the catalyst active.

(b) Selectivity of thecatalyst:

Theability of the catalyst to direct a reaction to yield a particular product isreferred to as the selectivity of the catalyst. For example, by using differentcatalysts, we can get different products for the reaction between H₂ andCO.

(i)

(ii)

(iii)

Question - 28 : -
Describe some features ofcatalysis by zeolites.

Answer - 28 : -

Zeolites are alumino-silicatesthat are micro-porous in nature. Zeolites have a honeycomb-like structure,which makes them shape-selective catalysts. They have an extended 3D-network ofsilicates in which some silicon atoms are replaced by aluminium atoms, givingthem an Al−O−Si framework. The reactions taking place in zeolites are verysensitive to the pores and cavity size of the zeolites. Zeolites are commonlyused in the petrochemical industry.

Question - 29 : -
What is shape selectivecatalysis?

Answer - 29 : -

A catalytic reaction whichdepends upon the pore structure of the catalyst and on the size of the reactantand the product molecules is called shape-selective catalysis. For example,catalysis by zeolites is a shape-selective catalysis. The pore size present inthe zeolites ranges from 260-740 pm. Thus, molecules having a pore size morethan this cannot enter the zeolite and undergo the reaction.

Question - 30 : -
Explain the following terms:
t.

Answer - 30 : -

(i) Electrophoresis (ii) Coagulation

(iii) Dialysis (iv) Tyndall effec

Answer

(i) Electrophoresis:

The movement of colloidalparticles under the influence of an applied electric field is known aselectrophoresis. Positively charged particles move to the cathode, whilenegatively charged particles move towards the anode. As the particles reachoppositely charged electrodes, they become neutral and get coagulated.

(ii) Coagulation:

The process of settling down ofcolloidal particles i.e., conversion of a colloid into a precipitate is calledcoagulation.

(iii) Dialysis

The process of removing adissolved substance from a colloidal solution by the means of diffusion througha membrane is known as dialysis. This process is based on the principle thations and small molecules can pass through animal membranes unlike colloidalparticles.

(iv) Tyndall effect:

When a beam of light is allowedto pass through a colloidal solution, it becomes visible like a column oflight. This is known as the Tyndall effect. This phenomenon takes place asparticles of colloidal dimensions scatter light in all directions.

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