NCERT Class – 9 Science Solution: Chapter 2 is Matter Around Us Pure-Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question: 12

Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?

Answer:

Crystallization

Crystallization

Question: 13

The ‘sea-water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment.

Answer:

  • Homogeneous — mixture of salts and water only
  • Heterogeneous — contains salts, water, mud, decayed plant etc.
Homogeneous and Heterogeneous Mixture

Question: 14

While diluting a solution of salt in water, a student by mistake added acetone (boiling point What technique can be employed to get back the acetone? Justify your choice.

Answer:

Distillation, since acetone is more volatile it will separate out first.

Question: 15

What would you observe when

  1. A saturated solution of potassium chloride prepared at is allowed to cool to room temperature.
  2. An aqueous sugar solution is heated to dryness.
  3. A mixture of iron filings and sulphur powder is heated strongly.

Answer:

  1. Solid potassium chloride will separate out.
  2. Initially the water will evaporate and then sugar will get charred.
  3. Iron sulphide will be formed.

Question: 16

Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.

Answer:

  • Particle size in a suspension is larger than those in a colloidal solution.
  • Also molecular interaction in a suspension is not strong enough to keep the particles suspended and hence they settle down.

Question: 17

Smoke and fog both are aerosols. In what way are they different?

Answer:

  • Both fog and smoke have gas as the dispersion medium.
  • The only difference is that the dispersed phase in fog is liquid and in smoke it is a solid.

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