NCERT Solutions for Class 12 Chemistry Chapter 5 Surface Chemistry updated and modified according to new CBSE syllabus 2022-2023. Get here intext and exercises question answers of class 12 Chemistry unit 5 in Hindi and English Medium.

NCERT Solutions for Class 12 Chemistry Chapter 5

Surface Chemistry

Surface chemistry deals with phenomena that occur at the surfaces or interfaces. The interface or surface is represented by separating the bulk phases by a hyphen or a slash. For example, the interface between a solid and a gas may be represented by solid-gas or solid/gas. Due to complete miscibility, there is no interface between the gases. For example:

    • (i) The bulk phase can be a pure compound or a solution.
    • (ii) The bulk phases may be solid – liquid, solid – gas, solid – vacuum, liquid – gas etc.

Class 12 Chemistry Chapter 5 MCQ

Q1

Colloidion is 4% solution of which one of the following in alcohol-ether mixture.

[A]. Nitroglycerin
[B]. Cellulose acetate
[C]. Glycol di-nitrate
[D]. Nitrocellulose
Q2

Volume of one mole of any gas at NTP is

[A]. 11.2 litre
[B]. 22.4 litre
[C]. 10.2 litre
[D]. 22.8 litre
Q3

The nature of bonding forces in adsorption are

[A]. Purely physical such as Van der Waal’s forces
[B]. Purely chemical
[C]. Both chemical and physical
[D]. Sometimes physical and sometimes chemical.
Q4

Tyndall effect confirms the

[A]. Gravity effect on the solution particles
[B]. Light scattering by the solution particles
[C]. Heterogeneous nature of solutions
[D]. Brownian motion of the solution particles

Adsorption

The phenomenon of attracting and retaining 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. It is also called the positive adsorption.
Example:
Adsorption of water vapours on silica gel in air conditioners.
Example: Absorption of water in a sponge.

Distinction between Adsorption and Absorption

In adsorption, the substance is concentrated only at the surface and does not penetrate through the surface to the bulk of the adsorbent, while in absorption, the substance is uniformly distributed throughout the bulk of the solid.
Example:
when a chalk stick is dipped in ink, the surface retains the colour of the ink due to adsorption of coloured molecules while the solvent of the ink goes deeper into the stick due to absorption. On breaking the chalk stick, it is found to be white from inside.
Both adsorption and absorption can take place simultaneously also. The term sorption is used to describe both the processes.

12th Chemistry Unit 5 Multiple Choice Questions

Q5

Which is favourable for physical adsorption?

[A]. High T and high P
[B]. High T and low P
[C]. Low T and high P
[D]. T and P do not affect
Q6

Which of the following is not correct for enzyme catalysis?

[A]. The enzyme activity is maximum at optimum pH which is between 5-7
[B]. Each enzyme is specific for a given reaction
[C]. The favourable temperature range of enzyme activity is between 50⁰ – 60°C
[D]. The enzymatic activity is increased in presence of certain substances called co-enzymes
Q7

Milk is an example of

[A]. Emulsion
[B]. Suspension
[C]. Foam
[D]. Solution
Q8

The term sorption stands for

[A]. Absorption
[B]. Adsorption
[C]. Both absorption and adsorption
[D]. Desorption

Applications of Adsorption

The phenomenon of adsorption finds a number of applications. Important ones are listed here:

    • (i) Production of high vacuum
    • (ii) Gas mask
    • (iii) Control of humidity
    • (iv) Removal of colouring matter from solutions
    • (v) Heterogeneous catalysis
    • (vi) Separation of inert gases
    • (vii) In curing diseases
    • (viii) Froth floatation process
    • (ix) Adsorption indicators
    • (x) Chromatographic analysis
Promoters and Poisons

Promoters are substances that enhance the activity of a catalyst while poisons decrease the activity of a catalyst. For example, in Haber’s process for manufacture of ammonia, molybdenum acts as a promoter for iron which is used as a catalyst.
Poison is the substance which slows down the activity of catalyst.

Enzyme Catalysis

Enzymes increase the rate of chemical reactions without themselves being consumed or permanently altered by the reaction. Second, they increase reaction rates without altering the chemical equilibrium between reactants and products.
Some Enzymatic Reactions:

EnzymeSourceEnzymatic reaction
InvertaseYeastSucrose ⟶ Glucose and fructose
ZymaseYeastGlucose ⟶ Ethyl alcohol and carbon dioxide
DiastaseMaltStarch ⟶ Maltose
MaltaseYeastMaltose ⟶ Glucose
UreaseSoyabeanUrea ⟶ Ammonia and carbon dioxide
PepsinStomachProteins ⟶ Amino acids
Colloids

Colloids are mixtures in which microscopically dispersed insoluble particles of one substance are suspended in another substance. The size of the suspended particles in a colloid can range from 1 to 1000 nanometers. The types of colloids include sol, emulsion, foam, and aerosol.

Class 12 Chemistry Chapter 5 Important Questions

Write observations for the following: (i) when an electric current is passed through a sol (ii) when a beam of light is passed through a sol (iii) when an electrolyte (NaCl) is added to ferric hydroxide sol.

(i) When an electric current is passed through a sol., electrophoresis occurs as +ve charged particles move towards the cathode and -ve charged particles move towards the anode.
(ii) When a beam of strong light is passed through a colloidal solution, the Tyndall effect occurs.
(iii) When an electrolyte (NaCl) is added to the ferric oxide solution, then coagulation will take place.

What is the effect of temperature on adsorption?

Adsorption decreases with increase in temperature because adsorption is exothermic process.

Define the terms – catalysis and catalyst.

Catalysis: The phenomenon in which a small quantity of a substance known as catalyst alters the rate of a reaction is known as catalysis.
Catalyst: The substance which alter the rate of a reaction and themselves remain chemically and quantitatively unchanged after the reaction are known as catalysts.

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