NCERT · Class 9 · Science

Chapter 2: Is Matter Around Us Pure?

Practice each question, then open the answer or worked solution.

Exercise-2.2

Textbook page 18 · 3 questions

Q1Written answer

Differentiate between homogenous and heterogeneous mixtures with examples.

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Worked solution

The following are the differences between heterogeneous and homogenous mixtures.

Heterogeneous mixture	Homogeneous mixture
All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope	Particles are uniformly distributed throughout the mixture
Irregular composition	Has a uniform composition
Noticeable boundaries of division	No apparent boundaries of division
Examples: Seawater, blood, etc.	Examples: Rainwater, vinegar, etc.

Q2Written answer

How are sol, solution and suspension different from each other?

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Worked solution

Attributes	Sol	Solution	Suspension
Type of mixture	Heterogeneous	Homogeneous	Heterogeneous
Size of particles	10^-7 – 10^-5cm	Less than 1nm	More than 100nm
Tyndall effect	Exhibited	Not exhibited	May or may not be exhibited
Appearance	Usually glassy and clear	Unclouded and clear	Cloudy and opaque
Visibility	Visible with an ultramicroscope	Not visible	Visible with the naked eye
Diffusion	Diffuses very slowly	Diffuses rapidly	Do not diffuse
Stability	Pretty stable	Highly stable	Unstable
Settling	Get settled in centrifugation	Do not settle	Settle on their own
Example	Milk, blood, smoke	Salt solution, sugar solution	Sand in water, dusty air

Q3Written answer

To make a saturated solution, 36g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

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Worked solution

Mass of solute (NaCl) = 36 g

Mass of solvent (H₂O) = 100 g

Mass of solution (NaCl + H₂O) = 136 g

Concentration = Mass of solute/Mass of solution x 100

Concentration = 36/136 x 100 = 26.47%

Hence, the concentration of the solution is 26.47%