Is Matter Around Us Pure? Class 9 Science 20 Important Questions with answer

20 important questions along with their answers for the Class 9 Science chapter "Is Matter Around Us Pure?".

Important Questions and Answers

1. What is a pure substance?

   • Answer: A pure substance consists of a single type of particle. All constituent particles of the substance have the same chemical nature. Examples include elements like gold, silver, and compounds like water, carbon dioxide.

2. What is a mixture?

   • Answer: A mixture contains more than one kind of pure substance mixed together physically. Examples include air, soil, and seawater.

3. Differentiate between homogeneous and heterogeneous mixtures.

   • Answer:
     • Homogeneous Mixture: The composition is uniform throughout. Examples: Salt in water, sugar in water.
     • Heterogeneous Mixture: The composition is not uniform throughout. Examples: Oil and water, sand and iron filings.

4. What are solutions?

   • Answer: A solution is a homogeneous mixture of two or more substances. The substance present in a smaller amount is called the solute, and the one in a larger amount is the solvent. Examples: Salt in water, sugar in water.

5. Define solubility.

   • Answer: Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specified temperature.

6. What is a suspension?

   • Answer: A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. These particles can be seen with the naked eye. Examples: Muddy water, flour in water.

7. What is a colloid?

   • Answer: A colloid is a heterogeneous mixture in which the particle size is between 1 nm to 1000 nm. The particles do not settle down when left undisturbed. Examples: Milk, fog.

8. What is the Tyndall effect?

   • Answer: The Tyndall effect is the scattering of light by colloidal particles. It is observed when light passes through a colloid and the path of the light becomes visible. Examples: Beam of light in fog.

9. How can you separate a mixture of salt and sand?

   • Answer: The mixture of salt and sand can be separated by:
     • Dissolving the mixture in water (salt dissolves, sand does not).
     • Filtration to separate sand.
     • Evaporation to recover salt from the water.

10. What are alloys?

    • Answer: Alloys are homogeneous mixtures of metals, or metals and non-metals. Examples: Brass (copper and zinc), Steel (iron and carbon).

11. What is chromatography?

    • Answer: Chromatography is a technique used for the separation of those solutes that dissolve in the same solvent. It is based on the different rates of movement of solutes on a stationary phase when a solvent moves over it.

12. What is distillation?

    • Answer: Distillation is a process used for separating components of a mixture based on differences in their boiling points. It involves boiling the liquid to form vapor and then condensing the vapor back into a liquid.

13. How can you separate a mixture of two immiscible liquids?

    • Answer: A mixture of two immiscible liquids can be separated using a separating funnel based on their different densities.

14. What is crystallization?

    • Answer: Crystallization is a process used to purify a solid. A saturated solution is prepared and then allowed to cool slowly. The pure substance forms crystals and separates out.

15. What are physical changes?

    • Answer: Physical changes are changes in the physical properties of a substance without any change in its chemical composition. Examples: Melting of ice, boiling of water.

16. What are chemical changes?

    • Answer: Chemical changes result in the formation of new substances with different properties. Examples: Rusting of iron, burning of wood.

17. Explain the process of filtration.

    • Answer: Filtration is a method used to separate an insoluble solid from a liquid by passing the mixture through a filter. The solid particles are retained by the filter, while the liquid passes through.

18. What is decantation?

    • Answer: Decantation is the process of separating a liquid from a solid by gently pouring the liquid from the container, leaving the solid undisturbed.

19. What is the difference between evaporation and boiling?

    • Answer:
      • Evaporation: Occurs at the surface of the liquid and at all temperatures.
      • Boiling: Occurs throughout the liquid and at a specific boiling point.

20. Describe the process of centrifugation.

    • Answer: Centrifugation is a process used to separate suspended particles from a liquid by spinning the mixture at high speed. The denser particles move outward to the bottom of the container, while the less dense liquid remains on top.

These questions and answers provide a comprehensive overview of the key concepts in the chapter "Is Matter Around Us Pure?" for Class 9 Science.