2nd PUC Chemistry Question Bank Chapter 5 Surface Chemistry

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Karnataka 2nd PUC Chemistry Question Bank Chapter 5 Surface Chemistry

Question 1.
What is adsorption?
Answer:
The accumulation of molecular species at the surface of the solid or liquid is termed as adsorption.

Question 2.
What is adsorbate?
Answer:
The molecular species or substance which accumulates at the surface is called adsorbate.

Question 3.
What is adsorbent?
Answer:
The surface of the material on which adsorption takes place is called adsorbent.

Question 4.
Give an example for adsorption process.
Answer:
Silica gel adsorbs water molecules.
Silica gel → Adsorbent.
Water molecules → Adsorbate.

Question 5.
Give two differences between adsorption and absorption.
Answer:

Adsorption	Absorption
(a) Accumulation of molecular species over the surface of the solid or liquid.	(a) Uniform entry of one substance throughout the body of the other substance.
(b) surface phenomenon	(b) Bulk phenomenon

Question 6.
How ΔH, ΔS and ΔG changes during adsorption?
Answer:
During adsorption ΔH becomes -ve [decreases], ΔS becomes +ve [increases] and ΔG becomes -ve [decreases],

Question 7.
What happens to entropy of gas after adsorption?
Answer:
Decreases.

Question 8.
What is physical adsorption? Give three characteristics.
Answer:
When the particles of the adsorbate are held to the surface of the adsorbent by weak van der Waals forces, the adsorption is called physical adsorption or physisorption.
Characteristics:

• It is not specific in nature.
• It is reversible in nature.
• Adsorption decreases as temperature increases.

Question 9.
What is chemical adsorption? Give three characteristics.
Answer:
When the molecules of the adsorbate are held to the surface of the adsorbent by the chemical bonds, the adsorption is called chemical adsorption or chemisorption.
Characteristics:

• It is specific in nature.
• It is irreversible in nature.
• Adsorption increases as temperature increases.

Question 10.
Give two characteristics of chemisorption?
Answer:

• It is specific in nature.
• It is irreversible in nature.
• Adsorption increases as temperature increases.

Question 11.
Give three differences between physical adsorption and chemisorption.
Answer:

Physical adsorption	Chemisorption
1. It arises because of weak van der Waals forces.	1. It is caused by strong chemical bonds.
2. It is not specific in nature	2. It is specific in nature
3. It is reversible in nature	3. It is irreversible in nature
4. Low temperature is favourable for this adsorption.	4. High temperature is favourable for this adsorption.

Question 12.
Out of physical adsorption and chemisorption which one has lower enthalpy of adsorption?
Answer:
Physical adsorption.

Question 13.
What is the effect of temperature and pressure on the adsorption of gas over the solid surface?
Answer:
As pressure increases adsorption increases, as temperature increases adsorption decreases.

Question 14.
When is a solid good adsorbent?
Answer:
When the solid is .in finely divided state.

Question 15.
Give reason “activated charcoal is used in gas mask”.
Answer:
Activated charcoal adsorbs poisonous gases.

Question 16.
Name the adsorbent used in removal of colouring matter.
Answer:
Animal charcoal/ Activated carbon/ Charcoal.

Question 16A.
Give a Freundlich adsorption isotherm equation.
Answer:

x is mass of the gas adsorbed.
m is mass of the adsorbent.
p is pressure.
K₁ and n are constants.

Question 17.
Give four applications of adsorption.
Answer:

1. In the production of high vaccum.
2. In gas masks: Activated charcoal is used to adsorb poisonous gases.
3. Removal of colouring matter from solutions,
4. In heterogeneous catalysis.

Question 18.
Give two applications of adsorption.
Answer:

1. In the production of high vaccum.
2. In gas masks: Activated charcoal is used to adsorb poisonous gases.
3. Removal of colouring matter from solutions,
4. In heterogeneous catalysis.

Question 19.
What is homogeneous catalysis? Give three examples.
Answer:
At catalytic process in which reactant and the catalyst are in the same phase, then the process is called homogeneous catalysis.
Example (1) : Oxidation of sulphur dioxide to sulphur trioxide.

NO is a catalyst.
Example (2) : Acid hydrolysis of methylacetate

Example (3) : Acid hydrolysis of canesugar

Question 20.
Give an example for homogenous catalysis.
Answer:
At catalytic process in which reactant and the catalyst are in the same phase, then the process is called homogeneous catalysis.
Example (1) : Oxidation of sulphur dioxide to sulphur trioxide.

NO is a catalyst.
Example (2) : Acid hydrolysis of methylacetate

Example (3) : Acid hydrolysis of canesugar

Question 21.
What is homogenous catalysis? Give an example.
Answer:
At catalytic process in which reactant and the catalyst are in the same phase, then the process is called homogeneous catalysis.
Example (1) : Oxidation of sulphur dioxide to sulphur trioxide.

NO is a catalyst.
Example (2) : Acid hydrolysis of methylacetate

Example (3) : Acid hydrolysis of canesugar

Question 22.
Write the catalyst used in the decomposition of potassium chlorate to get potassium chloride and oxygen.
Answer:
Manganese dioxide [MnO₂].

Question 23.
What is heterogeneous catalysis? Give an example.
Answer:
A catalytic process in which the reactants and the catalyst are in different phases is known as heterogeneous catalysis.
Example (1): Oxidation of sulphur dioxide to sulphur trioxide in presence of platinum catalyst.

Example (2): Combination of hydrogen and nitrogen to form ammonia.

Example (3): Hydrogenation of vegetable oil

Question 24.
Explain the adsorption theory of heterogeneous catalysis.
Answer:

• Reactant molecules adsorb on the surface of the catalyst, there by increasing the concentration of the various reactant molecules on the surface of the catalyst.
• Adsorption being exothermic process, the heat of adsorption is utilised in enhancing the rate of the reaction.
• Occurrence of chemical reaction on the catalyst’s surface through the formation of an intermediate between catalyst and reactants.
• Desorption of reaction products from the catalyst surface and thereby making the surface available again for more reaction to occur.

Question 25.
what are catalytic promoters? Give example.
Answer:
Promoters are the substances that enhances (increases) the activity of the catalyst.
Example: In the manufacture of ammonia by Haber’s process molybdenum is a promoter to the catalyst iron.

Question 26.
What are catalytic poisons?
Answer:
Catalytic poisons are the substances which reduce the activity of the catalyst.

Question 27.
What is the activity of the catalyst?
Answer:
The ability of a catalyst to increase the rate of a reaction is called activity of the catalyst. The activity of catalyst depends upon the strength of chemisorption between reactants and the catalyst.

Question 28.
What is selectivity of the catalyst? Give an example.
Answer:
The selectivity of a catalyst is its ability to direct a reaction to yield a particular product.
Example: With CO and H₂ using different catalyst gives different products.

Question 29.
What is shape selective catalysis? Give an example of such type of catalyst.
Answer:
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.
Example : Zeolites, ZSM-5.

Question 30.
Name the shape selective catalyst used to convert alcohol into petrol (gasoline).
Answer:
ZSM – 5

Question 31.
What are enzymes?
Answer:
Enzymes are proteins which catalyse many biochemical reactions.

Question 32.
Give four characteristics of enzymes.
Answer:

• Enzymes are highly specific in nature.
• Highly active under optimum temperature. Enzyme activity is maximum in human body at 310 K (37° C).
• Highly active under optimum pH.
• Enzymatic activity is increased by the presence of certain substances known as co-enzymes.

Question 33.
Name the enzyme used in the inversion of cane sugar.
Answer:
Invertase.

Question 34.
Name the enzyme used in the conversion of
1. Glucose or Fructose to Ethyl alcohol
2. Starch to Maltose
3. Maltose to Glucose
4. Urea to Ammonia
5. Protein to Amino acids
6. Milk to Curd
Answer:
1. Zymase
2. Diastase
3. Maltase
4. Urease
5. Pepsin
6. Lacto bacilli.

Question 35.
Explain the mechanism of enzyme catalysis?
Answer:
Step I: There are a number of active centres on the surface of the enzyme. The molecules of the reactant (substrate) which have complementary shape to the enzyme fit into these active centres like a key fits into a lock and forms an activated complex.

Step II: Decomposition of activated complex gives the products.

Question 36.
What is colloid?
Answer:
Colloid is a heterogeneous system in which one substance of the size 1 nm to 1000 nm is dispersed in another substance called dispersion medium.

Question 37.
What is sol? Give examples.
Answer:
Sol is a colloidal solution in which solid is a dispersive phase and liquid is a dispersion medium.
Example: Gold sol, paints.

Question 38.
What is emulsion? Give examples.
Answer:
Emulsion is a colloidal solution in which both dispersive phase and dispersion medium are liquids.
Examples : Milk, hair cream.

Question 39.
What is gel? Give examples.
Answer:
Gel is a colloid in which liquid is a dispersive phase and solid is a dispersion medium. Example: Butter, cheese.

Question 40.
What is lyophillic colloid? Give example.
Answer:
Colloidal solution in which the particles of the dispersed phase have a great affinity for the dispersion medium.
Example: Gelatin sol, starch sol.

Question 41.
What is lyophobic colloid? Give example.
Answer:
The colloidal solutions in which there is no affinity between the particles of the dispersed phase and the dispersion medium are called lyophobic colloids. Example: Gold sol, As₂S₃ sol.

Question 42.
Mention any three differences between lyophilic sols and lyophobic sols.
Answer:

Lyophilic sols (Colloids)	Lyophobic sols (Colloids)
1. Colloidal particles have affinity for dispersion medium.	1. Colloidal particles do not have affinity for dispersion medium.
2. These are very stable.	2. These are unstable.
3. These are reversible in nature.	3. These are irreversible in nature.
4. Viscosity is higher than that of dispersion medium.	4. Viscosity is same as that of dispersion medium.

Question 43.
What are mutlimolecular colloids? Give examples.
Answer:
The colloids in which large number of atoms or smaller molecules (dispersive phase) aggregate together to form the particles having the size in the colloidal range are called multimolecular colloids.
Example: Gold sol, sulphur sol.

Question 44.
What are macromolecular colloids? Give example.
Answer:
Solution in which macromolecules (dispersed phase particles) have size in the colloidal range are called macromolecular colloids.
Example: Starch sol, proteins.

Question 45.
What are associated colloids? Give example.
Answer:
Some substances at higher concentrations exhibit colloidal behaviour due to the formation of a aggregates. This type of colloids are called associated colloids.
Example: Micelle formed by sodium sterate.

Question 46.
What is Kraft temperature?
Answer:
The formation of micelle takes place only above a particular temperature called Kraft (T_k) temperature.

Question 47.
What is CMC (Critical Micelle Concentration)?
Answer:
The formation of micelle takes place above a particular concentration called critical micelle concentration (CMC).

Question 48.
How gold sol is prepared by Breadig’s arc method?
Answer:

An electric arc is struck between electrodes of the metal immersed in the dispersion medium. The heat produced vapourises the metal which condenses to form particles of colloidal size.

Question 49.
What is peptization? Give an example.
Answer:
The process of converting the precipitate into colloidal sol in presence of small amount of electrolyte is called peptization.
Example: When freshly prepared precipitation of ferric hydroxide is treated with ferric chloride and shaken well the ferric hydroxide sol is obtained.

Question 50.
What is dialysis? Explain.
Answer:
It is a process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane.

The bag of suitable membrane containing the colloidal solution is suspended in a vessel through which fresh water is continuously flowing. The molecules and ions diffuse through membrane into the outer water and pure colloidal solution is left behind.

Question 51.
What is tyndall effect? Explain.
Answer:
Scattering of light by colloidal particles is called tyndall effect.

When light is passed through colloidal solution and observed from a direction at right angles to the direction of light beam, the path of the beam is illuminated by a bluish light. This is called Tyndall effect.
The Tyndall effect is due to the scattering of light by colloidal particles.

Question 52.
What is Brownian movement? What is the cause for it?
Answer:
In dispersion medium, colloidal particles are in continuous zig zig random motion in all directions. This type of kinetic motion of the colloidal particles is called Brownian movement.

Brownian movement is due to the bombardment between the colloidal particles and the particles of dispersion medium.

Question 53.
What is zeta potential?
Answer:
The potential difference between the fixed layer and the diffused layer of opposite charges formed on the surface of the colloids is called zeta potential or electro kinetic potential.

Question 54.
What is an electrophoresis? Explain.
Answer:
The movement of colloidal particles under an applied electric potential is called electrophoresis.

The existance of charges on colloidal particles is confirmed by electrophoresis experiment.
When electric potential is applied across. 2 platinum electrodes dipping in a colloidal solution, the colloidal particles move either to cathode or to an anode depending upon charge carried by the colloids.

Positively charged particles move towards the cathode and negatively charged particles move towards the anode.

Question 55.
What is coagulation or precipitation of colloids?
Answer:
The process of setting of colloidal particles is called coagulation or precipitation of the sol.

Question 56.
Mention the role of alum in the purification of drinking water?
Answer:
It acts as a coagulating agent.

Question 57.
Name two methods by which a lyophilic sol can be coagulated.
Answer:

1. By electrophoresis.
2. By mixing two oppositely charged sols.
3. By boiling.
4. By addition of-electrolytes.

Question 58.
Name the phenomenon/effect for the following.
1. Colloidal particles are in zig-zag motion.
2. When electric potential is applied across the two platinum electrode dipping in colloidal solution, particles move towards one or the other electrodes.
3. Scattering of light by colloidal sols.
Answer:
1. Brownian movement.
2. electrophoresis
3. Tyndal effect.

Question 59.
Give reason for the following.
(a) Brownian movement of colloidal particles.
(b) Stability of colloids.
(c) The movement of colloidal particles towards cathode in the electric field.
Answer:
(a) Collision of colloidal particles with the solvent molecules.
(b) Adsorption of ions on its surface.
(c) Colloidal particles are positively charged.

Question 60.
As₂S₃ sol is negatively charged, between sodium nitrate and aluminium nitrate which one is needed in large quantity to coagulate the above sol.
Answer:
Sodium nitrate.

Question 61.
state Hardy – Schulze rule.
Answer:
Greater the valence of the coagulating ion added, the greater is its power to cause coagulation.

Question 62.
1. What is tyndall effect?
2. In the coagulation of negative sol. arrange the following ions in the ascending order of their flocculating power Ba²⁺, Na⁺, Al³⁺
Answer:
1. Scattering of light by colloidal particles is called tyndall effect.

When light is passed through colloidal solution and observed from a direction at right angles to the direction of light beam, the path of the beam is illuminated by a bluish light. This is called Tyndall effect.
The Tyndall effect is due to the scattering of light by colloidal particles.
2. Decreasing order Al³⁺ > Ba²⁺ > Na⁺.

Question 63.
For positive sol arrange the coagulation power of the following active ions in the decreasing order, Cl, PO₄^3-, [Fe (CN)₆]^4-, SO₄^2-
Answer:
Decreasing order : (Kc (CN)₆]^4- > PO₄^3- > SO₄^2- > Cl^–

Question 64.
What is oil dispersed in water (o/w) type emulsion? Give example.
Answer:
In this emulsion, oil acts as dispersive phase and water acts as dispersion medium.
Example: Milk and Vanishing cream. In milk, fat acts as dispersive phase and water acts as dispersion medium.

Question 65.
What is water dispersed in oil (w/o) type emulsion? Give example.
Answer:
In this emulsion, water acts as dispersive phase and oil acts as dispersion medium.
Example : Butter, cream.

Question 66.
What are emulsions? (Give an example of oil dispersed in water (o/w) type emulsion.
Answer:
Emulsion is a colloidal solution in which both dispersive phase and dispersion medium are liquids.
Examples : Milk, hair cream.

In this emulsion, oil acts as dispersive phase and water acts as dispersion medium.
Example: Milk and Vanishing cream. In milk, fat acts as dispersive phase and water acts as dispersion medium.

Question 67.
Give four applications of colloids.
Answer:

1. In electrical precipitation of smoke.
2. In purification of drinking water.
3. Cleaning action of soaps and detergents.
4. In leather tanning.

Question 68.
How is smoke precipitated using cottrel precipitator.
Answer:
Smoke is an aerosol of negative charged carbon and dust particles in air.

Precipitation of smoke particles is carried out by cottrel precipitator.
Smoke is allowed to pass through a chamber containing plates charged to a very high potential, charged particles of the smoke get precipitated.

Question 69.
Give an example of an oil dispersed in water emulsion.
Answer:
Milk.

Question 70.
Mention the role of alum in the purification of drinking water.
Answer:
It acts as coagulating agent.

Question 71.
Give reason:
1. Potash alum is used in the clarification of water.
2. A solid catalyst is very efficient in the finely divided state.
3. Lyophilic sols are more stable than lyophobic sols.
Answer:
1. Potash alum coagulates muddy particles in water.
2. Finely divided catalyst has larger surface area.
3. Lyophillic sols are more hydrated or solvated.