Chemistry 3 Marks Question

1. Liquid loving/solvent loving.
2. Potential difference between the fixed layer and diffused/double layer of opposite charges.
3. Some substances at higher concentration exhibit colloidal behaviour due to formation of aggregates. The aggregated particles thus formed are called associated colloids or micelles.

1.  

Multimolecular colloid	Associated colloid
Aggregation of large number of small atoms or molecules.	Aggregation of large number of ions in concentrated solutions.

2.  

Coagulation	Peptization
Settling down of colloidal particles.	Conversion of precipitate into colloidal sol by adding small amount of electrolyte.

3.  

Homogenous catalysis	Heterogeneous catalysis
Reactants and catalyst are in same phase.	Reactants and catalyst are in different phases.

These are liquid-liquid colloidal systems or the dispersion of one liquid in another liquid.
Types:

1. Oil dispersed in water (O/W type) Example; milk and vanishing cream.
2. Water dispersed in oil (W/O type) Example; butter and cream.

1. Aerosol: A colloidal solution having a gas as the dispersion medium and a solid/liquid as the dispersed phase is called an aerosol. For example: Fog, Smoke, Dust.
2. Emulsion: The colloidal solution in which both the dispersed phase and dispersion medium are liquids is called an emulsion. For example: Milk, Cold Cream.
3. Micelles: There are some substances which at low concentrations behave as normal strong electrolytes, but at higher concentrations exhibit colloidal behaviour due to the formation of aggregates. The aggregated particles thus formed are called micelles. eg. Soap, Detergents.

1. Electrophoresis takes place when sol particles move towards opposite electrodes due to attraction.
2. Tyndall effect will be observed due to scattering of light by colloidal particles.
3. Coagulation takes place (due to neutralisation of charges.)

1. Coagulation takes place due to neutralisation of charges.
2. Tyndall effect will be observed due to scattering of light by colloidal particles.
3. Electrophoresis takes place in which sol particles moves towards oppositely charged electrodes due to attraction.

1. Ferric hydroxide sol is positively charged. By adding potassium chloride, the excess chloride ions neutralize its positive charge and cause it to coagulate.
2. The dispersed phase and dispersion medium migrate towards oppositely charged electrodes (electrophoresis).
3. The beam of light is scattered by colloidal particles(Tyndall effect).

1. Shape-Selective catalysis: The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis e.g. zeolites.
2. Dialysis: Removal of soluble impurities from sols by a semipermeable membrane is known as dialysis. e.g. ferric hydroxide sol is purified by this method.

1. Multimolecular colloids: When a large number of atoms or smaller molecules of a substance aggregate together to form species having size (with diameters less than 1nm) in the colloidal range are called multimolecular colloids. e.g. a gold sol, sulphur sol.
2. Macromolecular colloids: When the size of the macromolecules may be in the colloidal range such systems are called macromolecular colloids. e.g. starch, cellulose, proteins, enzymes.

	Physisorption	Chemisorption
1.	Because of van der Waals forces.	Caused by chemical bond formation.
2.	Reversible.	Irreversible.
3.	Enthalpy of adsorption is low(20-40 kJ/mol).	Enthalpy of adsorption is high(80-240)kJ/mol.

1. It is a process in which both adsorption and absorption can take place simultaneously.
2. It is the potential difference between the fixed layer and the diffused/double layer of opposite charges around the colloidal particles.
3. It is the temperature above which the formation of micelles takes place.

1. Lyophobic are liquid (dispersion medium)-hating and lyophilic are liquid (dispersion medium)-loving colloids.
2. Solution is a Homogenous mixture while colloid is heterogeneous mixture/does not show Tyndall effect-shows Tyndall effect.
3. Homogeneous catalysis: reactants and catalyst are in same phase-Heterogeneous catalysis: reactants and catalyst are not in same phase.

1. Mutual coagulation.
2. Strong interaction between dispersed phase and dispersion medium or solvated layer.
3. CO acts as a poison for catalyst.

1. Micelles: Micelles are associated colloids which show colloidal behaviour at high concentration and act as strong electrolytes at low concentration.
2. Peptization: The process of converting a precipitate into colloidal sol by shaking itwith dispersion mediumin the presence of a small amount of electrolyte is called Peptization.
3. Desorption: The process of removing an adsorbed substance froma surface onwhich it is adsorbed is called desorption.

1. Production of vacuum: The remaining traces of air can be adsorbed by charcoal from a vessel to create a vacuum.
2. Heterogeneous catalysis: Adsorption of reactants on the solid surface of the catalysts increases the rate of reaction.
3. Froth floatation process: In this process, sulphide ore is concentrated by using pine oil which adsorbs the ore particles and imurities are wetted by water which settle at the bottom.

Multimolecular colloids	Macromolecular colloids
They are aggregates of molecules less than 1nm thick. Example: Sulphur Sol.	They themselves are large molecules of colloidal dimensions. Example: Starch.

Associated colloids – are those which at low concentration behave as normal electrolytes & at high concentration act as colloids.

1. -An aerosol is a colloidal solution of solid or liquid (dispersed phase) in gas (dispersion medium) eg smoke, dust, fog, mist, cloud.
2. -A hydrosol is a colloidal solution of solid (dispersed phase) in water (dispersion medium) eg starch sol, protein sol, biological fluids.
3. -An emulsion is a colloidal solution of liquid (dispersed phase) in liquid (dispersion medium) eg milk, cream.

• Lyophilic sols are solvent attracting sol.

Ex. Gum, gelatine, starch, rubber.

• Lyophobic sols are solvent repelling sol.

Ex. Metal sols, metal sulphides.
Lyophobic sols are readily coagulated because they are not stable.

Adsorption- The phenomenon of attraction and retention of the molecules of a substance on the surface of a liquid or a solid resulting into a higher concentration of the molecules on the surface is called adsorption.

Physisorption	Chemisorption
It usually takes place at low temperature and decreases with increasing temperature.	It takes place at relatively high temperatures.
It is not very specific i.e. all gases are adsorbed on all solids to some extent.	It is highly specific and takes place when there is some possibility of compound formation between the adsorbate and the adsorbent molecules.
Multi Molecular layers may be formed on the adsorbent.	Usually mono-molecular layer is formed on the absorbent.

1. When light beam is passed through both the solutions, path of light becomes visible in a colloidal solution (due to scattering of light by colloidal particles).
2. Four applications of adsorption are following-

1. In chromatography for separation of mixtures.
2. Adsorption of toxic gases by activated charcoal in gas masks.
3. Decolourization of cane sugar by animal charcoal.
4. In heterogeneous catalysis.

S. No.	Physisorption	Chemisorption
1.	Happens due to van der Waal forces.	Caused by a chemical bond.
2.	It's not specific in nature and reversible in nature.	Highly specific in nature and irreversible.
3.	It depends on the nature of the gas. More liquefiable gas is adsorbed easily.	Depend on the nature of the gas. those gases can react with the adsorbent show chemisorption.
4.	Enthalpy of adsorption is low around 20-40kJ/ mol.	Enthalpy if adsorption is high around 80-240kJ/ mol.
5.	Low temperature required.	High temperature is required.
6.	It depends on the surface area. Higher the area high in the process rate.	High activation energy is needed sometimes.
7.	Results in multimolecular layers on the adsorbent surface.	Result is unimolecular.

1. Decreases.
2. Increases.
3. Increases.

Internal phase of Dispersed phase	External phase or Dispersion medium	Colloidal name	Example
Solid	Solid	Solid sols	Alloys, Ruby glass, Gems or precious stones, marbles, optical and vision glasses.
	Liquid	sols	Muddy water, gold sol, protein, starch, agar, gelatin in water, paints, pigments in water.
	Gas	Aerosols (or solids	Smoke, particulate clouds.
Liquid	Solids	Gels	Cheese, jems, jellies, plants, fruits, vegetables.
	Liquid	Emulsions	Butter, milk, cosmetic products, e.g., shampoo, creams, emulsified oils, polish and medicines.
	Gas	Aerosols (or liquids)	Fog, clouds, mist.
Gas	Solid	Solid foams	Pumicestone, styrene foam, foamed rubber, porous pot. thermocole rubber pillows and mattresses.
	Liquid	Foams and froths	Lather, soap seeds, air bubble.
	Gas	Homogeneous system	Do not exist as colloids.

Adsorption plays an important role in heterogeneous catalysis. Adsorption is surface phenomenon in which the substances (reactants) get concentrated only on the surfaces of solid adsorbents and do not penetrate into it.This increases concentration of reactants and there is a great probability of occurrence of reaction. The catalyst adsorbs reactants and forms a intermediate compound known as activated complex. Following are various ways in which catalytic adsorption increases the reaction rate:

1. The concentration of reactants on surface of solid adsorbent increases and it becomes easier for molecules to attack each other for effective collisions, forming products.
2. A particular part of reactant molecule may come in contact with other molecules which otherwise is difficult.
3. Some adsorbed molecules dissociate into atoms or free radicals which are very reactive and thus increase the reaction rate.
4. Heat of adsorption released provides activation energy for formation of activated complex and then increase the rate of reaction.

The influence is in the following ways:

1. Smaller the size of the particles of the adsorbent, greater is the surface area and greater is the adsorption.
2. At constant temperature, adsorption first increases with increase of pressure and then attains equilibrium at a high pressure.
3. In physical adsorption, it decreases with increase of temperature but in chemisorption, first it increases and then decreases.

There are some substances which at low concentration behave as normal electrolyte but at higher concentrations exhibit colloidal behaviour due to formation of aggregated particles. The aggregated particles thus formed are called micelles. Surface active agents such as soaps and detergents are the example of micelle forming substances.The formation of micelles takes place only above a particular temperature called Kraft temperature and above a particular concentration called critical micelle concentration (CMC). On dilution, these colloids revert back to individual ions.

1. In multi-molecular colloids, the colloidal particles are an aggregate of atoms or small molecules with a diameter of less than 1 nm. The molecules in the aggregate are held together by van der Waal's forces of attraction. Examples of such colloids include gold sol and sulphur sol.
2. In macro-molecular colloids, the colloidal particles are large molecules having colloidal dimensions. These particles have a high molecular mass. When these particles are dissolved in a liquid, sol is obtained. For example: starch, nylon, cellulose, etc.
3. Certain substances tend to behave like normal electrolytes at lower concentrations. However, at higher concentrations, these substances behave as colloidal solutions due to the formation of aggregated particles. Such colloids are called aggregated colloids.

When gaseous molecules come in contact with the surface of a solid catalyst, a weak chemical combination takes place between the surface of the catalyst and the gaseous molecules, which increases the concentration of reactants on the surface. Different molecules adsorbed side by side have better chance to react and form new molecules. This enhances the rate of reaction. Also, adsorption is an exothermic process. The heat released in the process of adsorption is utilised in enhancing the reaction rate.