NCERT Solutions Class 9 Science Chapter 2 - Is Matter Around Us Pure ?

Is Matter Around Us Pure – Important Questions with Answers

1. Define pure substance. Give two examples.
Answer: A pure substance consists of a single type of particle with a fixed composition.
Examples: Distilled water and oxygen gas.

2. What is a mixture? Name its types.
Answer: A mixture is a combination of two or more substances that are not chemically combined.
Types: Homogeneous and Heterogeneous mixtures.

3. Differentiate between homogeneous and heterogeneous mixtures.
Answer:

4. What is a solution? Give one example.
Answer: A solution is a homogeneous mixture of two or more substances.
Example: Sugar dissolved in water.

5. Define solute and solvent with examples.
Answer:

• Solute: The substance that is dissolved (e.g., salt).

• Solvent: The substance that dissolves the solute (e.g., water).

6. Why is water called a universal solvent?
Answer: Water dissolves more substances than any other liquid, making it a universal solvent.

7. Define suspension. Give one characteristic.
Answer: A suspension is a heterogeneous mixture in which solute particles do not dissolve but remain suspended.
Characteristic: Particles settle on standing.

8. What is a colloid? Give an example.
Answer: A colloid is a mixture where very small particles of one substance are evenly dispersed in another.
Example: Milk.

9. List any three differences between solution, suspension, and colloid.
Answer:

10. What is Tyndall effect? Name one mixture that shows it.
Answer: Tyndall effect is the scattering of light by colloidal particles.
Example: Fog or milk.

11. State two methods of separating components of a mixture.
Answer:

• Filtration

• Evaporation

12. What is the principle behind the technique of chromatography?
Answer: Different components of a mixture travel at different speeds on a stationary phase.

13. Why is chromatography useful? Give one application.
Answer: It helps to separate and identify components of a mixture.
Application: Separating pigments in ink.

14. Name the method used to separate salt from sea water.
Answer: Evaporation.

15. How can pure water be obtained from a salt solution?
Answer: By the process of distillation.

16. What is distillation?
Answer: Distillation is the process of separating components of a mixture based on different boiling points.

17. Differentiate between evaporation and distillation.
Answer:

• Evaporation: Used for separating volatile solvent from non-volatile solute.

• Distillation: Used to separate a mixture of liquids based on boiling points.

18. What is a centrifuge? Mention its use.
Answer: A centrifuge is a device that separates components of a mixture using centrifugal force.
Use: Separating cream from milk.

19. How can you test the purity of a substance?
Answer: By checking its melting or boiling point; pure substances have fixed points.

20. Define alloy. Is it a pure substance or a mixture?
Answer: An alloy is a homogeneous mixture of two or more metals (or metals and non-metals).
It is a mixture, not a pure substance.

21. Give one difference between a compound and a mixture.
Answer:

• Compound: Elements are chemically combined in a fixed ratio.

• Mixture: Substances are physically mixed in any proportion.

22. What is the composition of air?
Answer: Air is a mixture of gases: 78% nitrogen, 21% oxygen, and 1% other gases.

23. Is tap water a pure substance? Explain.
Answer: No, tap water contains dissolved salts and impurities, so it is a mixture.

24. What are the characteristics of a compound? (Any two)
Answer:

• Has fixed composition.

• Components lose their individual properties.

25. Why can a mixture be separated by physical methods but a compound cannot?
Answer: Because the components of a mixture are not chemically bonded, while in compounds they are.