Important Question Is Matter Around Us Pure Chapter 2 Science Class 9 CBSE Board

Important Questions For All Chapters – Science Class 9

Short Questions

1. What is a pure substance?
Answer: A pure substance is a form of matter that contains only one kind of particles having the same chemical nature throughout. It has uniform composition and definite properties.

2. What is a mixture?
Answer: A mixture is a combination of two or more pure substances which are mixed in any proportion and can be separated by physical methods.

3. Give one example of a homogeneous mixture.
Answer: An example of a homogeneous mixture is salt dissolved in water, where the composition is uniform throughout.

4. Give one example of a heterogeneous mixture.
Answer: A mixture of oil and water is an example of a heterogeneous mixture because its composition is not uniform.

5. What is a solute?
Answer: The component of a solution that gets dissolved in the solvent and is usually present in a smaller amount is called the solute. For example, sugar in sugar solution.

6. What is a solvent?
Answer: The component of a solution that dissolves the solute and is generally present in a larger amount is called the solvent. For example, water in a sugar solution.

7. What is the Tyndall effect?
Answer: The scattering of light by the particles of a colloidal solution is known as the Tyndall effect. This effect makes the path of light visible through the colloid.

8. What is a suspension?
Answer: A suspension is a heterogeneous mixture in which the solid particles do not dissolve but remain suspended throughout the medium and can be seen with the naked eye.

9. What are metals?
Answer: Metals are elements that are generally lustrous, malleable, ductile, and good conductors of heat and electricity. Examples include copper, silver, and iron.

10. What type of change is melting of ice?
Answer: Melting of ice is a physical change because no new substance is formed and the composition of water remains the same.

Long Questions

1. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer: Homogeneous mixtures have a uniform composition throughout and the components cannot be distinguished visually. Examples include air and salt solution.
Heterogeneous mixtures do not have a uniform composition and their components can be seen separately. Examples include sand and water or oil and water.

2. What is a solution? Explain its main properties.
Answer: A solution is a homogeneous mixture of two or more substances. It consists of a solute and a solvent.

Properties:

• It has uniform composition throughout.
• The particles are smaller than 1 nanometre and cannot be seen by the naked eye.
• The particles do not scatter light; hence, the path of light is not visible.
• The solute particles cannot be separated by filtration.
• A solution is stable and does not settle down on standing.

3. Define solute and solvent with examples.
Answer: The solute is the substance that gets dissolved in a solvent. The solvent is the substance that dissolves the solute.
For example, in a sugar solution, sugar is the solute and water is the solvent.

4. What are the types of mixtures? Give examples.
Answer: There are two main types of mixtures:

• Homogeneous mixtures: have uniform composition throughout, such as salt water or air.
• Heterogeneous mixtures: have non-uniform composition, such as soil or oil and water.

5. What are the properties of a suspension?
Answer:

• A suspension is a heterogeneous mixture.
• Its particles are large enough to be seen with the naked eye.
• The particles scatter a beam of light and make its path visible.
• The particles settle down when left undisturbed, making it unstable.
• The components can be separated by filtration.

6. What is a colloidal solution? Explain its properties.
Answer: A colloidal solution is a heterogeneous mixture in which the particles are uniformly spread throughout the dispersion medium.

Properties:

• Colloids show the Tyndall effect.
• The particles are too small to be seen with naked eyes.
• They do not settle down on standing and are quite stable.
• They cannot be separated by filtration but can be separated by centrifugation.

7. What is the Tyndall effect? Explain with an example.
Answer: The Tyndall effect is the scattering of light by particles of a colloid or a suspension.
Example: When sunlight passes through the canopy of a dense forest, the path of light becomes visible due to tiny water droplets in the air, which act as colloidal particles.

8. Differentiate between solution, suspension, and colloid.
Answer: 

9. What is a saturated solution? Explain with an example.
Answer: A saturated solution is a solution that contains the maximum amount of solute that can dissolve in a solvent at a given temperature. For example, when no more salt can dissolve in water at a certain temperature, the solution becomes saturated.

10. Differentiate between physical and chemical changes with examples.
Answer:

• Physical change: No new substance is formed and the change is reversible. Example: melting of ice, boiling of water.
• Chemical change: A new substance with different properties is formed and the change is irreversible. Example: burning of wood, rusting of iron.

11. What is an element? Give its characteristics.
Answer: An element is a pure substance that cannot be broken down into simpler substances by chemical reactions.

Characteristics:

• Contains only one type of atom.
• Has definite physical and chemical properties.
• Cannot be decomposed into simpler substances.
  Examples: hydrogen, oxygen, iron.

12. What is a compound? Explain with an example.
Answer: A compound is a substance formed when two or more elements combine chemically in a fixed proportion.
For example, water (H₂O) is formed when hydrogen and oxygen combine in a fixed ratio of 2:1. The properties of water are completely different from those of hydrogen and oxygen.

13. Distinguish between metals and non-metals.
Answer:

14. Differentiate between mixtures and compounds.
Answer: 

15. Describe an activity to show the difference between a mixture and a compound using iron and sulphur.
Answer: Take a small amount of iron filings and sulphur powder. Mix them well and divide into two parts.

• Part 1 (Mixture): The mixture shows both yellow and black colours. The iron particles can be separated using a magnet.
• Part 2 (Heated Compound): Heat the mixture until it becomes red hot. A new black substance called iron sulphide is formed. It is not attracted by a magnet and has properties different from its elements.
  This shows that heating causes a chemical change and forms a compound, while simple mixing forms a mixture.