Q: Which one of the following characteristics is associated with adsorption?

ΔH ΔG ΔS < 0 Adsorption process is accompanied of decrease in entropy.

Q: Fog is the colloidal solution of:

Fog is a colloidal solution in which liquid droplets are dispersed in gas.

Q: Which property of colloids is not dependent on the charge on colloidal particles?

Tyndall effect is optical property.

Q: Which one of the following statements is not correct?

A catalyst decreases activation energies of both the forward and backward reaction by same amount, therefore, it speeds up both forward and backward reaction by same rate.Equilibrium constant is therefore not affected by catalyst at a given temperature.

Q: Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.

During adsorption, the concentration of one substance on the surface of other substance is much higher than the concentration in the bulk. On the other hand, during absorption, there is uniform distribution of molecules of one substance throughout the body of other substance.Thus, silica gel adsorbs water vapour while anhydrous calcium chloride absorbs water.

Q: What is the difference between physisorption and chemisorption?

Physisorption (Physical adsorption)Chemisorption (Chemical adsorption) Weak van der Waals forces are present between the adsorbate molecules and the adsorbent.Strong chemical forces similar to chemical bonds are present between the adsorbate molecules and the adsorbent.The enthalpy of adsorption is low (20 to 40 kJ/mol).The enthalpy of adsorption is high (40 to 400 kJ/mol). Occurs at low temperature and decreases with an increase in temperature. Occurs at high temperature and increases with increase in temperature. It is reversible.It is irreversible. No significant activation energy is required.Usually, high activation energy is required. It forms multimolecular layers.It forms unimolecular layers.

Q: Give reason why a finely divided substance is more effective as an adsorbent.

Finely divided substance has larger surface area and greater adsorption. Hence, it is more effective as an adsorbent.

Question 1

Measuring Zeta potential is useful in determining which property of colloidal solution?

Accepted Answer

In colloidal solution, the potential difference between the fixed layer and the diffused layer of opposite charge is known as Zeta potential.The presence of equal and similar charges on colloidal particles is largely responsible in providing stability to the colloidal solution.

Question 2

Which mixture of the solutions will lead to the formation of negatively charged colloidal [Agl]l−sol ?

Accepted Answer

50 mL of 1MAgNO3+50ml of 1.5MKI- The colloidal sol AgI is prepared by adding KI solution to the AgNO3​ solution till KI is in slight excess, iodide ion I−will be absorbed in the surface of AgI particles thereby giving them a negative charge: AgI+I−→AgI:I−- The reaction that takes place when AgNO3​ and KI react together can be depicted as: AgNO3​(aq)+KI(s)→AgI(aq)+KNO3​(aq)- Thus, for surrounding the silver iodide with iodide ion, the concentration of KI must be slightly more than AgNO3​. Thus, the concentration will be 50 mL of 1MAgNO3+50ml of 1.5MKI

Question 3

On which of the following properties does the coagulating power of an ion depend?

Accepted Answer

Coagulation of colloidal solution by using an electrolyte depends on the charge present (positive or negative) on colloidal particles as well as on its size.- Coagulating power of an electrolyte depends on the magnitude of charge present on effective ion of electrolyte.

Question 4

Which one of the following characteristics is associated with adsorption?

Accepted Answer

ΔH ΔG ΔS < 0 Adsorption process is accompanied of decrease in entropy.

Question 5

Fog is the colloidal solution of:

Accepted Answer

Fog is a colloidal solution in which liquid droplets are dispersed in gas.

Question 6

Which property of colloids is not dependent on the charge on colloidal particles?

Accepted Answer

Tyndall effect is optical property.

Question 7

Which one of the following statements is not correct?

Accepted Answer

A catalyst decreases activation energies of both the forward and backward reaction by same amount, therefore, it speeds up both forward and backward reaction by same rate.Equilibrium constant is therefore not affected by catalyst at a given temperature.

Question 8

Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.

Accepted Answer

During adsorption, the concentration of one substance on the surface of other substance is much higher than the concentration in the bulk. On the other hand, during absorption, there is uniform distribution of molecules of one substance throughout the body of other substance.Thus, silica gel adsorbs water vapour while anhydrous calcium chloride absorbs water.

Question 9

What is the difference between physisorption and chemisorption?

Accepted Answer

Physisorption (Physical adsorption)Chemisorption (Chemical adsorption) Weak van der Waals forces are present between the adsorbate molecules and the adsorbent.Strong chemical forces similar to chemical bonds are present between the adsorbate molecules and the adsorbent.The enthalpy of adsorption is low (20 to 40 kJ/mol).The enthalpy of adsorption is high (40 to 400 kJ/mol). Occurs at low temperature and decreases with an increase in temperature. Occurs at high temperature and increases with increase in temperature.  It is reversible.It is irreversible. No significant activation energy is required.Usually, high activation energy is required. It forms multimolecular layers.It forms unimolecular layers.

Question 10

Give reason why a finely divided substance is more effective as an adsorbent.

Accepted Answer

Finely divided substance has larger surface area and greater adsorption. Hence, it is more effective as an adsorbent.

Question 11

What are the factors which influence the adsorption of a gas on a solid?

Accepted Answer

The factors which influence the adsorption of a gas on a solid are as given below:(1) Nature of the gas(2) Nature of adsorbent(3) Specific area of adsorbent(4) Effect of temperature(5) Effect of pressure(6) Activation of adsorbent

Question 12

What is an adsorption isotherm? Describe Freundlich adsorption isotherm?

Accepted Answer

Adsorption isotherm is the variation of the mass of the gas (adsorbate) adsorbed per gram of the adsorbent with pressure at constant temperature.The Freundlich adsorption isotherm is the mathematical representation for the variation of the extent of adsorption (x/m) with pressure (P) at a given temperature. Here, x is the mass of adsorbate and m is the mass of adsorbent. The expression is mx​=k×Pn1​,

Question 13

What do you understand by activation of adsorbent? How is it achieved?

Accepted Answer

Activation of adsorbent is the increasing of the adsorbing power of the adsorbent. It means increasing the rate of adsorbption. it can be achieved by the following methods.(1) To activate metallic adsorbents, their surface is made rough by mechanical rubbing or by depositing finely dispersed metals on the surface of adsorbent by electroplating or by some chemical reactions.(2) Increase the surface area by sub-dividing into smaller pieces.(3) Strongly heat in contact with super heated steam or in vacuum at a temperature of 623-1273 K. This removes already adsorbed gases.

Question 14

What role does adsorption play in heterogeneous catalysis?

Accepted Answer

Heterogeneous catalysis usually involves gaseous reactants and solid catalyst. Due to physisorption or chemisorption, the reactant molecules are adsorbed on the surface of the solid catalyst. This increases the reactant concentration on the catalyst surface and the rate of the reaction. One of the reactant molecule fragments on catalyst surface and produces active sites which increase the rate of the reaction. The product molecules with no affinity for the adsorbent desorb and catalyst surface becomes free for adsorption of other catalyst molecules. This is in accordance with the adsorption theory.

Question 15

Why is adsorption always exothermic?

Accepted Answer

During adsorption, energy is released due to presence of attraction between adsorbate and adsorbent molecules. Hence, adsorption is an exothermic process.

Question 16

How are the colloidal solutions classified on the basis of physical states of the dispersed phase and dispersion medium?

Accepted Answer

On the basis of physical states of the dispersed phase and dispersion medium,  the colloidal solutions classified into eight types of colloidal systems as shown in the following table. Note: A mixture of gas with another gas is a homogeneous mixture and not a colloidal solution. Dispersed phaseDispersion medium Type of colloidal solution Example  Solid Solid  Solid sol Alloys Solid   Liquid Sol Paints  Solid  Gas Aerosol Smoke Liquid  Solid Gel Jelly Liquid   Liquid Emulsion Milk  Liquid  Gas Aerosol Mist Gas  Solid Solid sol Pumice Gas   Liquid Foam Soap

Question 17

Discuss the effect of pressure and temperature on the adsorption of gases on solids.

Accepted Answer

Effect of pressure on the adsorption of gases on solids:When temperature is constant and pressure is increased, the extent of adsorption increases. This is in accordance with Le chatelier's principle.Effect of temperature on the adsorption of gases on solids:Adsorption is an exothermic process as heat is evolved during adsorption. With increase in temperature, the extent of adsorption will decrease. This is in accordance with Le chatelier's principle.Desorption is an endothermic process as heat is absorbed during desorption. With increase in temperature, the extent of desorption will increase. This is in accordance with Le chatelier's principle.

Question 18

What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?

Accepted Answer

In lyophilic sols, the dispersed phase particles have great affinity (or love) for the dispersion medium. These sols are reversible. Examples include gum, gelatin, starch, proteins and rubber etc.In lyophobic sols, the dispersed phase particles have no affinity (or love) for the dispersion medium. These sols are irreversible. Examples include solutions of metals such as gold and silver, metal hydroxides and metal sulphides.The hydrophobic sols are less stable and easily coagulated than hydrophilic sols because, the stability of  hydrophobic sols is due to charge only and the stability of hydrophilic sols is due to charge and solvation/ hydration.

Question 19

What is the difference between multimolecular and macromolecular colloids? Give one example of each. How are associated colloids different from these two types of colloids?

Accepted Answer

The difference between multimolecular and macromolecular colloids is shown:Multimolecular colloidsMacromolecular colloids The colloidal particles are aggregates of a large number of atoms or molecules having a diameter of less than 1 nm.The colloidal particles are macromolecules having a very large molecular mass. Weak van der Waals forces are present between particles.Strong chemical bonds are present between macromolecular particles. Sulphur sol is a multimolecular colloid and contains S8 molecules while starch is a macromolecular colloid.Associated colloids (soaps and detergents) behave as normal electrolytes at low concentrations and show colloidal properties at high concentrations due to the formation of aggregated particles called micelles.

Question 20

What are enzymes ? Write in brief the mechanism of enzyme catalysis.

Accepted Answer

Enzymes are complex organic compounds containing nitrogen and catalyze biochemical reactions that occur in living beings. Enzymes are produced by living cells. Enzymes are proteins with molar mass ranging from 15,000 to 1,000,000 g/mol.The mechanism for enzyme catalysis includes following steps:(1) Enzyme (E) binds to substrate (S) to form enzyme substrate complex (ES)E+S⇌ESThis step is fast and reversible.(2) Enzyme substrate complex (ES) converts to enzyme product (EP) complexES→EPThis is slow step (rate determining step)(3) Enzyme product complex (EP) dissociates into enzyme (E) and products (P)EP→E+P

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