NIOS Class 12 Chemistry Chapter 8 Colloids

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NIOS Class 12 Chemistry Chapter 8 Colloids

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Colloids

Chapter: 8

Module – III: States of Matter

INTEXT QUESTIONS 8.1

1. Classify the following into suspension, colloidal solution and true solution. milk, sugar in water, clay in water, blood, boot polish, sand in water, face cream, jelly, foam.

Ans: Suspension – Clay in water, Sand in water.

Colloidal – Milk, Blood, Boot polish, Face Cream, Jelly, Foam.

True Solution – Sugar in water.

2. Give one example each of:

(a) Sol.

(b) Gel.

(c) Aerosol.

(d) Emulsion?

Ans: Sol– Starch in water.

Gel– Silica gel.

Aerosol – Fog.

Emulsion – Milk.

3. What is the difference between an alcosol and hydrosol?

Ans: 

Basis	Alcosol	Hydrosol
Dispersing medium	Alcohol	Water
Nature	Colloidal solution in alcohol	Colloidal solution in water
Example	Colloidal solution of sulphur in alcohol	Colloidal solution of gold in water

4. How does colloidal solution differ from true solution.

Ans: 

True Solution	Colloidal Solution
1. Size of solute particles is less than 1 nm.	1. Size of colloidal particles is 1–100 nm.
2. Forms a transparent solution and allows light to pass through without scattering.	2. Path of light becomes visible due to scattering (Tyndall effect).

Thus, a colloidal solution differs from a true solution mainly in particle size and behaviour towards light.

INTEXT QUESTIONS 8.2

1. Name two colloids that can be prepared by Bredig’s Arc method.

Ans: Gold sol, Platinum sol.

2. Name two colloids that can be prepared by chemical methods.

Ans: As2S3, Fe(OH)³ (Arsenious sulphide sol, ferric hydroxide sol)

3. Differentiate between (a) Lyophilic and Lyophobic sol. (b) macromolecular and multimolecular colloids.

Ans:

Lyophilic sol	Lyophobic sol
(i) Easy to prepare.	(i) Prepared by special methods.
(ii) Strong affinity between dispersed phase and dispersion medium.	(ii) Little or no affinity between dispersed phase and dispersion medium.
(iii) Reversible in nature.	(iii) Irreversible in nature.

Macromolecular colloids	Multimolecular colloids
(i) Colloidal particles are large molecules whose size lies in the colloidal range.	(i) Individual particles are not of colloidal size.
(ii) Formed by single large molecules such as polymers.	(ii) Formed by aggregation of a large number of small molecules or atoms.
(iii) Example: Starch, proteins.	(iii) Example: Gold sol, sulphur sol.

4. Explain the formation of micelle.

Ans: Formation of Micelle: A micelle is a structure formed by surfactant molecules in a liquid, typically water. Surfactants have both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts.

TERMINAL EXERCISE

1. List three differences between a true solution and a colloidal solution.

Ans: 

Basis	True Solution	Colloidal Solution
(i) Particle size	Particles are molecular or ionic in size (< 1 nm)	Particles are larger (1–1000 nm)
(ii) Filterability	Pass through filter paper and semipermeable membranes	Pass through filter paper but not through semipermeable membranes
(iii) Appearance	Transparent and homogeneous	Translucent or opaque due to Tyndall effect