NCERT Class – 9 Science solution: Chapter 2 Is Matter Around Us Pure-Part 5

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Question: 18

Classify the following as physical or chemical properties

  1. The composition of a sample of steel is: iron, carbon and other elements.

  2. Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.

  3. Metallic sodium is soft enough to be cut with a knife.

  4. Most metal oxides form alkalis on interacting with water.

Answer:

  • Physical properties – (a) and (c)

  • Chemical properties – (b) and (d)

    Image of difference between physical and chemical properties

    Image of Difference between Physical and Chemical Properties

    Image of difference between physical and chemical properties

Question: 19

The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a (mass by volume) solution of sodium hydroxide ‘A’ dissolved of in of water, ‘B’ dissolved of in of water while ‘C’ dissolved of in water to make of solution. Which one of them has made the desired solution and why?

Answer:

‘C’ has made the desired solution

Mass by volume %

Question: 20

Name the process associated with the following

  1. Dry ice is kept at room temperature and at one atmospheric pressure.

  2. A drop of ink placed on the surface of water contained in a glass spreads throughout the water.

  3. A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.

  4. A acetone bottle is left open and the bottle becomes empty.

  5. Milk is churned to separate cream from it.

  6. Settling of sand when a mixture of sand and water is left undisturbed for some time.

  7. Fine beam of light entering through a small hole in a dark room, illuminates the particles in its paths.

Answer:

  1. Sublimation

  2. Diffusion

  3. Dissolution/diffusion

  4. Evaporation, diffusion

  5. Centrifugation

  6. Sedimentation

  7. Scattering of light (Tyndall effect)

Question: 21

You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at and sample ‘B’ boils at . Which sample of water will not freeze at ? Comment.

Answer:

  • Sample ‘B’ will not freeze at because it is not pure water.

  • At 1 atm, the boiling point of pure water is and the freezing point of pure water is