Important Questions Class 12 Chemistry Chapter 5

Surface Chemistry is a small and simple chapter in Class 12 that can be well understood if proper attention is paid. This chapter covers a variety of topics, including adsorption—its types and applications, catalysis, colloids—preparation, purification, and properties, emulsions and so on.

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Extramarks provides Chapter 5 Class 12 Important Questions for students to study in detail. These questions will help students to understand the types of questions which can be expected in exams. The answers are taken from NCERT books and are well explained in easy language so that any further doubts are cleared during practice or overview of these questions. Moreover these questions are compiled by subject matter experts according to the latest CBSE guidelines.

CBSE Class 12 Chemistry Chapter-5 Important Questions

Study Important Questions for Class 12 Chemistry Chapter 5 – Surface Chemistry

Class 12 Chemistry Important Questions are critical for gaining a thorough understanding of the chapter and learning all of the fundamental concepts. These questions are divided into categories like ‘Very Short’ and ‘Short’ questions which carry 1, 2 or 3 marks.

Some of these questions are discussed below:

Very Short Questions – 1 Mark

Q1. Explain the purpose of impregnating the filter paper with a colloidal solution.

Ans. Impregnating the ultra-filter sheets with a colloidal solution reduces the pore size of the filter paper, allowing colloidal particles to be trapped while contaminants pass through.

Q2. “Chemisorption is a highly specific process.” Explain with an example.

Ans. Chemisorption is unique in nature because the molecules are held in place by a chemical bond on the solid surface. Metals, for example, absorb oxygen due to oxide formation and metals absorb hydrogen due to hydride formation. Because they will only be absorbed on metal, they are chemisorption selective.

Q3. Indicate the sign of entropy change that occurs when a substance’s molecules are adsorbed on a solid surface.

Ans. The entropy of a system is defined as its degree of randomness. As a result, when the molecule of a substance is adsorbed on a solid surface, its randomness decreases. As a result, the entropy will be negative.

Q4. “Finely divided adsorbents are more effective.” Why?

Ans. Finely split substances such as nickel or platinum, as well as porous materials such as charcoal and silicon gel, have a high surface area. Physisorption and chemisorption increase with increasing surface area. As a result, a finely divided material works well as an adsorbent.

Q5. What role does the Brownian movement play in the stability of sols?

Ans. Brownian motion produces a stirring effect. The particles are prevented from settling as a result of this effect. As a result, it affects the stability of the sol by preventing sol particles from settling.

Short Answer Type Questions – 2 Mark

Q1. Define the term peptisation and explain why it occurs.

Ans. Peptisation is the process by which a precipitate is converted into colloidal particles after the addition of an electrolyte.

The electrolyte that is added is referred to as a peptising agent. When an electrolyte is applied to a freshly precipitated substance, the precipitate particles absorb one type of electrolyte ion preferentially and scatter due to electrostatic repulsion. The colloidal size of particles is determined by this. Freshly manufactured precipitates that are expected to be in the colloidal solution are preferred.

Q2. Explain how temperature affects the extent of physical and chemical adsorption.

Ans. The kinetic energy of the gas molecules increases as the temperature rises, and they leave the surface of the adsorbent. As a result, the amount of adsorption decreases as the temperature rises. Chemical adsorption increases with increasing temperature until a certain point, after which it gradually declines.

Q3. Give two examples of emulsifying agents for oil in water (o/w) and water in oil (w/o) emulsions.

Ans. For o/w emulsions, proteins, gums, synthetic soaps, and other emulsifying agents; for w/o emulsions, heavy metal salts of fatty acids, long-chain alcohols and other emulsifying agents.

Q4. Propose a mechanism for an enzyme-catalysed reaction.

Ans. An enzyme attracts substrates to its active site, catalyses the chemical reaction that results in products, and then dissociates the products (separate from the enzyme surface). An enzyme-substrate complex is made up of an enzyme and its substrates.

Q5. Give an explanation of the following:

(a) Spraying electrified sand on clouds can produce artificial rain.

(b) Smoke electrical precipitation

Ans. (a) Clouds are formed by the colloidal dispersion of water particles in air. These water particles have a charge on them. When an aeroplane sprays oppositely charged colloidal dust or sand particles over a cloud, the colloidal water particles in the cloud are neutralised, causing them to approach closer and grow in size, eventually coagulating or pre-coagulating.

(b) Electrostatic smoke precipitators work by passing polluted flue gas (the gas that exits a chimney) through two electrodes (electrical terminals) inside a pipe or smokestack, which can be metal wires, bars or plates. The first electrode is subjected to a very high negative voltage. As they pass by, the dirt particles pick up a negative charge. A second electrode is located higher up the pipe (or further along if it is a horizontal pipe) and is made of metal plates charged to a high positive voltage. Because opposite charges attract, negatively charged soot particles are drawn to and adhere to positively charged plates. To empty the soot, the collecting plates must be shaken from time to time; this can be done manually.

Q6. Give an example of the “Hardy Schulze Rule.”

Ans. According to the Hardy-Schulze rule, the higher the valency of an electrolyte’s opposingly charged ion, the faster it coagulates. Electrostatic forces drive the attraction. Coagulation power is proportional to flocculation ion valency. Trivalent cations, for example, Al3+, are thought to be more effective at coagulating negatively charged arsenious sulphide sol.

Q7. What exactly is an emulsifying agent? What part does it play in the formation of an emulsion?

Ans. Emulsifying agents (emulsifiers) are chemicals that are soluble in both fat and water and aid in the even distribution of fat in water as an emulsion (they stabilise emulsions). They function by reducing interfacial tension and forming a stable interfacial layer between the two phases.

Short Answer Type Questions – 3 mark

Q1. What distinguishes the following colloids in terms of dispersion medium and dispersed phase? Provide an example of each type.

(a) An aerosol

(b) A hydrosol

(c) An emulsion.

Ans. (a) An aerosol is defined as a colloidal dispersion of a liquid in a gas. For example, fog.

(b) A hydrosol is a colloidal sol of a solid that has been dispersed in water as a dispersion medium. Consider the starch solution as an example.

(c) An emulsion is formed when both the dispersed phase and the dispersion medium are in liquid form. Consider the case of oil in water as an example.

Q2. Using one example of each, differentiate between multimolecular, macromolecular, and associated colloids.

Ans. The following are the distinctions between multimolecular, macromolecular and associated colloids:

Multimolecular colloids	Macromolecular colloids	Associated colloids
Particles are smaller in size than colloidal particles.	The particle size is colloidal in nature.	They are mostly electrolytes.
They are made up of very small particles.	In nature, they are already macromolecular.	As ions, associated colloids exist at low concentrations.
For example, gold sol and sulphur sol.	For example, protein starch colloids.	For example, micelles in soap.

Q3. Give the difference between:

(a) Catalysts and enzymes

(b) Promoters and poisons

Ans. (a)The differences between catalysts and enzymes are as follows:

Catalysts	Enzymes
Catalysts are chemicals that increase the rate of a chemical reaction while decreasing the rate of the reaction itself.	Enzymes are proteins that aid in the conversion of a substrate to a product during chemical reactions.
Catalysts are substances with a low molecular weight.	Enzymes have a high molecular weight.
Catalysts are simple organic molecule structures.	Enzyme structures are made up of complex protein molecules.

(b) The differences between promoters and poisons are given below:

Promoters	Poisons
Catalytic Promoters are compounds that are not catalysts in and of themselves, but when added with catalysts in small amounts to boost their efficiency, are referred to as promoters or activators.	Catalytic poisons are substances that interfere with the catalyst’s ability to function.
Promoters are known to speed up the catalytic activity.	Poisons are the substances which slow down the activity of the catalyst.

FAQs (Frequently Asked Questions)

1. What is the Tyndall effect?

The Tyndall effect is the scattering of light by particles in a colloid or a particularly small solution. To be visible, the beam must be dispersed and reflected by the individual suspended particles.

The Tyndall effect can only be observed if two conditions are met:

The diameter of the dispersed particles is not significantly different from the wavelength of the light used;
The magnitudes of the dispersed phase and dispersion medium refractive indices are vastly different.

2. What are the differences between physisorption and chemisorption?

The following are the distinctions between physisorption and chemisorption:

In physisorption, the adsorbate is bonded to the surface by weak Van Der Waal forces of attraction, whereas in chemisorption, the adsorbate is bonded to the surface by a strong chemical bond (covalent or ionic bond).
Physisorption does not result in the formation of a new compound, whereas chemisorption results in the formation of a new compound on the surface.
Low temperature promotes physisorption, whereas high temperature promotes chemisorption.
Physisorption can be reversed, whereas chemisorption is irreversible.

3. What is Surface Chemistry? Give an example.

Surface chemistry is a branch of chemistry concerned with the phenomena that occur at the interface of two substances. A physical boundary known as a surface exists in every condensed phase, whether liquid or solid. This surface separates one phase from another. Interfaces between metals and gases, such as platinum and hydrogen, interfaces between two immiscible liquids, such as oil and water, or between a liquid and a gas, and so on are a few examples.

Important Questions Class 12 Chemistry Chapter 5