Chemistry 2 Marks Questions

Tyndall Effect:- The scattering of light by the colloidal particles present in a colloidal sol is called Tyndall effect.
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.

Coagulation is a process of aggregating together the colloidal particles so as to change them into large particles which ultimately settle as a precipitate. By electrophoresis, coagulation of lyophobic Sols can be carried out.

Properties that depend on the number of solute particles irrespective of their nature relative to the total number of particles present in the solution.
Osmotic Pressure.

1. Froth floatation method: This is based upon the preferential wetting of mineral/ore particles by oil while the gangue particles by water.
2. Electrolytic refining: Is based on the principle of deposition of pure metal on cathode.

	Dispersed phase	Dispersion Medium
Smoke	Solid	Gas
Milk	Liquid	Liquid

Lyophilic sols are solvent attracting sols whereas Lyophobic sols are Solvent repelling sols Lyophobic sols can be easily coagulated.

1. NaCN solution.
2. CO.

Physisorption	Chemisorption
It is not very specific.	It is highly specific.
It is usually takes place at low temperature and decreases with increasing temperature.	It takes place at high temperature.
It is reversible.	It is irreversible.
Low enthalpy of adsorption.	High enthalpy of adsorption.

The process of settling of colloidal particles is called coagulation or precipitation of the sol.

1. By Electrophoresis/ The collidal particles move towards oppositely charged electrodes.
2. By mixing two oppositely charged sols.
3. By addition of electrolytes/ When excess of an electrolyte is added the colloidal particles are precipitated.

Soap molecules form micelle around the oil droplet or dirt in such a way that hydrophobic part interacts with the oil droplet and hydrophilic part projects out. Micelles can be washed away on rinsing with water. Thus soap helps in emulsification and washing away of oil and fats.

Minimum quantity of an electrolyte required to cause precipitation of a sol is called its coagulating value. Greater the charge on flocculating ion and smaller is the amount of electrolyte required for precipitation, higher is the coagulating power of coagulating ion (Hardy-Schulze rule).

Cottrell’s smoke precipitator, neutralises the charge on unburnt carbon particles, coming out of chimney and they get precipitated and settle down at the floor of the chamber.

River water is a colloidal solution of clay and sea water contains lot of electrolytes. The point at which river and sea meet is the site for coagulation. Deposition of coagulated clay results in delta formation.

Micelle formation is done by substances such as soaps and detergents when dissolved in water. The molecules of such substances contain a hydrophobic and a hydrophilic part. When present in water, these substances arrange themselves in spherical structures in such a manner that their hydrophobic parts are present towards the centre, while the hydrophilic parts are pointing towards the outside (as shown in the given figure). This is known as micelle formation.

Clean surface of adsorbent is suitable for adsorption because if surface is covered with gases of air, it will not be available for adsorption.

Physisorption involves weak van der Waals forces which become weaker with rise of temperature. The chemisorption involves formation of chemical bonds involving activation energy. With increase of temperature, we reach the activated complex faster. Therefore, chemisorption process becomes faster.

When electric field is applied to colloidal solution then charged colloidal particles move towards oppositely charged electrodes. This phenomenon is called electrophoresis.

A positively charged colloidal solution of hydrated ferric oxide is formed. On adding sodium chloride, negatively charged chloride ions neutralise the positive charge of the colloidal solution. Coagulation of the sol takes place.

Colloidal particles are large in size and hence the number of particle is lesser than the true solution. The lesser number of particles causes lower colligative properties.

After the reaction is over between adsorbed reactants, the process of desorption is important to remove products and further create space for the other reactant molecules to approach the surface and react.

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

The colour of the colloidal solution depends on the wavelength of the light scattered by the colloidal particles which in turn depends on size and nature of the colloidal particle. Finest gold sol is red in colour, as the size of the particle increases, it appears purple, then blue and finally golden.

In Cottrell precipitator, charged smoke particles are passed through a chamber containing plates with charge opposite to the smoke particles. Smoke particles lose their charge on the plates and get precipitated.

Animal skin is colloidal, in nature and carries positive charge. Tannin is a negatively charged colloidal solution. When leather is soaked in tannin, mutual coagulation of the two takes place and leather gets hardened.

Colloidal particles can pass through ordinary filter paper because the pores are too large. However, the pores of filter paper can be reduced in size by impregnating with collodion solution to stop the flow of colloidal particles.

The gas molecules diffuse onto the surface of the catalyst and get adsorbed. After the chemical change, the products formed diffuse away from the surface of the catalyst setting the surface free for other reactant molecules to adsorb on the surface and give the product.

The factors which influence the adsorption of a gas on a solid are:

1. The nature of a gas adsorbate and nature of solid adsorbent.
2. Surface area of adsorbent.
3. Pressure of gas.
4. Temperature.
5. Activation of adsorbent.

At the time of setting, the sun is at horizon. The light emitted by the sun has to travel a relatively longer distance through the atmosphere. As a result, blue part of light is scattered away by the particulate in the atmosphere causing red part to be visible.

S.No.	Type of Colloid	Example
(i)	Associated colloid	Surface active agents such as soap (CMC is 10–4 to 10–3 mol L–1) and synthetic detergents.
(ii)	Multimolecular colloid	Sulphur sol, gold sol.

Two oppositely charged sols when mixed in almost equal proportions, neutralise their charges and get partially or completely precipitated. Such type of coagulation is called mutual coagulation.

Adsorption isobar for physical adsorption shows that the extent of adsorption decreases with the increase in temperature. The adsorption isobar of chemical adsorption shows that the extent of adsorption first increases and then decreases with the increase in temperature. The initial unexpected increase in the extent of adsorption with temperature is due to the fact that the heat supplied acts as activation energy required for chemical adsorption which is much more than that of physical adsorption.

Important characteristics of lyophilic sols:

1. They are reversible in nature, i.e., once the dispersed phase is separated from dispersion medium the sol can be made again by simply remixing with dispersion medium.
2. They are quite stable and are not easily coagulated.

The emulsifying agent forms an interfacial layer between suspended particles and the dispersion medium thereby stabilising the emulsion.

Four uses of emulsions:

1. Cleansing action of soaps is based on the formation of emulsions.
2. Digestion of fats in intestines takes place by the process of emulsification.
3. Antiseptics and disinfectants when added to water form emulsions.
4. The process of emulsification is used to make medicines.

Chemisorption involves formation of bond between gaseous molecules/ atoms and the solid surface for which high activation energy is required. Thus it is referred to as activated adsorption.

Unbalanced bombardment of the particles of dispersed phase by molecules of dispersion medium causes brownian motion. This stabilises the sol.

Due to excessive dialysis, traces of electrolyte which stabilises the colloids is removed completely, making the colloid unstable. As a result, coagulation takes place.

Hardy and Schulze rules:

1. The ions carrying charge opposite to that of sol particles are effective in bringing about the coagulation of sol.
2. Coagulating power of the electrolyte is directly proportional to the fourth power of the valency of the ions causing coagulation.

This is because the stability of lyophobic sol is only due to the presence of charge on the colloidal particles. On the other hand, the stability of lyophilic sol is due to charge on the colloidal particles as well as solvation of colloidal particles.

Enzymes are basically protein molecules of high molecular masses. These form colloidal solutions when dissolved in water. These are complex, nitrogenous organic compounds produced by living plants and animals. Enzymes are also called 'biochemical catalysts'.
Mechanism of enzyme catalysis:
On the surface of the enzymes, various cavities are present with characteristic shapes. These cavities possess active groups such as -NH2, -COOH etc. The reactant molecules having a complementary shape fit into the cavities just like a key fits into a lock. This leads to the formation of an activated complex. This complex then decomposes to give the product.
Hence,

Physical adsorption involves van der Waals’ forces, so any number of layers may be formed one over the other on the surface of the adsorbent. Chemical adsorption takes place as a result of the reaction between adsorbent and adsorbate. When the surface of adsorbent is covered with one layer, no further reaction can take place.

Sulphide ores are preferentially wetted by oils while the gangue is preferentially wetted by water .The ore particles get adsorbed on oil droplets and come to the surface where they can be collected as froth gangue is wetted by water and gets settled down. Eg. It is done for Pbs (Phosphate-buffered saline) ores.
Here, in this froth floatation process, low grade sulphide ores are concentrated by separating them from earthly and silicious (containing silicon) matter. Here, pine oil is used as the frothing agent. The sulphide ore is shaken with pine oil and water, the ore particles are adsorbed on froth that floats and the gangue particles settle down as discussed earlier.
Thus, role of adsorption in froth floatation process can be understood as following processes.

1. Adsorption of pine oil on sulphide ore particles.
2. Formation of emulsion takes place.
3. Froth is formed along with ore particles.
4. As sulphide are extracted using froth floatation method therefore, only sulphide ore particles will show these type of adsorbing tendency. It is showing shape selective catalysis.

At lower concentration soap forms a normal electrolytic solution with water. After a certain concentration called critical micelle concentration, colloidal solution is formed.

Colloidal particle shows Brownian movement. The Brownian movement has a stirring effect which does not permit the particles to settle and thus, is responsible for the stability of sols.