NCERT Class 9 Science Solutions: Chapter 2 – Is Matter around Us Pure Part 1

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Image of Pure Substances and Mixtures for Matter Around Us Pure

Image of Pure Substances and Mixtures for Matter Around Us Pure

Image of Pure Substances and Mixtures for Matter Around Us Pure

Question 1:

Q. What is meant by a pure substance?

A. A pure substance is the one that consist of a single type of particles, i.e., all constituent particles of the substance have the same chemical nature. Pure substance can be classified as elements or compounds.

Question 2:

Q. List the points of differences between homogeneous and heterogeneous mixtures.

A. A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example: salt in water, sugar in water, copper sulphate in water A heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example: sodium chloride and iron filling, salt and sulphur, oil and water

Exercise

Question 1:

Q. Differentiate between homogeneous and heterogeneous mixtures with example.

A. A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example, mixtures of salt in water, sugar in water, copper sulphate in water, iodine in alcohol, alloy, and air have uniform compositions throughout the mixtures.

On the other hand, a heterogeneous mixture is a mixture having a non- uniform composition throughout the mixture. For example, composition of mixtures of sodium chloride and iron fillings, salt and sulphur, oil and water, chalk power in water, wheat flour in water, milk and water are not uniform throughout the mixtures.

Question 2:

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

A. Sol is a heterogeneous mixture. In this mixture, the solute Particles are so small that they cannot be seen with the naked eye. Also they seem to be spread uniformly throughout the mixture. The Tyndall effect is observed in this mixture. For example: milk of magnesia, mud

Solution is a homogeneous mixture. In this mixture, the solute particles dissolve and spread uniformly throughout the mixture. The Tyndall effect is not observed in this mixture. For example: salt in water, sugar in water, iodine in alcohol, alloy

Suspensions are heterogeneous mixtures. In this mixture, the solute particles are visible to the naked eye, and remain suspended throughout the bulk of the medium. The Tyndall effect is observed in this mixture. For example: chalk power and water, wheat flour and water

Question 3:

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

A. Mass of solute (sodium chloride) = 36 g (Given)

Mass of solvent (water) = 100 g (Given)

Then, Mass of Solution = Mass of solute + Mass of solvent

Therefore, concentration (mass by mass percentage) of the solution

Question 1:

Q. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than ), which are miscible with each other?

A. A mixture of two miscible liquids having a difference in their boiling points more than can be separated by the method of distillation. Thus, kerosene and petrol can be separated by distillation.

Image result for image of separated by distillation for class 9 chapter 2

Process of Distillation

Image result for image of separated by distillation for class 9 chapter 2

In this method, the mixture of kerosene and petrol is taken in a distillation flask with a thermometer fitted in it. We also need a beaker, a water condenser, and a Bunsen burner. The apparatus is arranged as shown in the above figure. Then, the mixture is heated slowly. The thermometer should be watched simultaneously. Kerosene will vaporize and condense in the water condenser. The condensed kerosene is collected from the condenser outlet, whereas petrol is left behind in the distillation flask.

Question 2:

Q. Name the technique to separate

(i) Butter from curd

A. Butter can be separated from curd by centrifugation.

(ii) Salt from sea- water

A. Salt can be separated from sea- water by evaporation.

(iii) Camphor from salt

A. Camphor can be separated from salt by sublimation.

Question 3:

Q. What type of mixtures is separated by the technique of crystallization?

A. By the technique of crystallization, pure solids are separated from impurities. For example, salt obtained from sea is separated from impurities; crystals of alum (phitkari) are separated from impure samples.