NCERT Class – 9 Science solution: Chapter 1 Matter in Our Surroundings-Part 5

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Question 21

Look at Figure and suggests in which of the vessels A, B, C or D the rate of evaporation will be the highest? Explain.

Figure of the vessels A, B, C or D

Figure of the Vessels a, B, C or D

Figure of the vessels A, B, C or D

Answer:

  • (c) The rate of evaporation increases with an increase of surface area because evaporation is a surface phenomenon.

  • Also, with the increase in air speed, the particles of water vapour will move away with the air, which will increase the rate of evaporation.

Question 22

(a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.

(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?

Answer:

Sublimation

Image of Interconversion of States

Image of Interconversion of States

Image of Interconversion of States

(b) The amount of heat required to convert 1 kg of solid into liquid at one atmosphere pressure at its melting point is known as its latent heat of fusion.

Long Answer Questions

Question 23

You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Answer:

  • Naphthalene is insoluble in water but soluble in ether an organic solvent.

  • It is volatile at room temperature.

  • Ammonium chloride is soluble in water and volatile at higher temperature.

  • It decomposes on heating to dryness.

Figure shows the labelled diagram

Figure Shows the Labelled Diagram

Figure shows the labelled diagram

Question 24

It is a hot summer day; Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?

Answer:

  • Cotton being a better absorber of water than nylon helps in absorption of sweat followed by evaporation which leads to cooling.

  • So Priyanshi is more comfortable, whereas Ali is not so comfortable.