Extra 30 short-answer questions from the chapter:2 "Is Matter Around Us Pure" for Class 9 CBSE Science:-
1. What is a pure substance? Give two examples.
Answer:
A pure substance consists of only one type of particle and has a uniform composition throughout.
Examples:
Elements
– Gold, Iron
Compounds
– Water (H₂O), Carbon dioxide (CO₂)
2. What is the difference between elements and compounds?
Answer:
|
Property |
Element |
Compound |
|---|---|---|
|
Definition |
A pure substance made of one type of atom |
A substance formed by the chemical combination of two or more elements |
|
Separation |
Cannot be broken down further |
Can be broken down into simpler substances |
|
Examples |
Oxygen (O₂), Gold (Au) |
Water (H₂O), Carbon dioxide (CO₂) |
3. What is a mixture? How is it different from a compound?
Answer:
A mixture is a combination of two or more substances that retain their individual properties and can be separated by physical means.
Differences:
Mixtures can have variable compositions, but compounds have fixed compositions.
Mixtures can be separated physically, but compounds require chemical methods.
No chemical bonds exist between components in a mixture, whereas compounds have chemical bonding.
4. What are the types of mixtures? Give examples.
Answer:
Mixtures are of two types:
Homogeneous mixtures
– Composition is uniform. (e.g., salt solution, air)
Heterogeneous mixtures
– Composition is not uniform. (e.g., oil and water, sand and iron filings)
5. Differentiate between homogeneous and heterogeneous mixtures.
Answer:
|
Feature |
Homogeneous Mixture |
Heterogeneous Mixture |
|---|---|---|
|
Composition |
Uniform throughout |
Non-uniform |
|
Phases |
Single phase |
Two or more phases |
|
Example |
Sugar solution, Air |
Sand and water, Oil and water |
6. Define colloids and suspensions. Give examples.
Answer:
Colloid
– A mixture where small particles remain dispersed without settling. (e.g., Milk, Fog)
Suspension
– A mixture where solid particles are large enough to settle down. (e.g., Muddy water, Sand in water)
7. What is the Tyndall effect? Name two mixtures that show this effect.
Answer:
The Tyndall effect is the scattering of light by particles in a colloid or suspension.
Examples:
Milk
(Colloid)
Fog
(Colloid)
8. What are alloys? Give two examples.
Answer:
Alloys are homogeneous mixtures of two or more metals (or metals with non-metals).
Examples:
Brass
(Copper + Zinc)
Steel
(Iron + Carbon)
9. Define solution, solute, and solvent with an example.
Answer:
Solution
– A homogeneous mixture of solute and solvent. (e.g., Sugar solution)
Solute
– The substance that dissolves. (e.g., Sugar)
Solvent
– The substance in which the solute dissolves. (e.g., Water)
10. How can you separate a mixture of salt and water?
Answer:
By evaporation, heating the solution removes water, leaving salt behind.
11. What is centrifugation? Where is it used?
Answer:
Centrifugation is a process where a spinning force separates components based on density.
Uses:
Separating cream from milk
Blood component separation in labs
12. How can iron fillings be separated from a mixture of sand and iron?
Answer:
By using a magnet, iron gets attracted while sand remains behind.
13. Define filtration. Give one example.
Answer:
Filtration is a method used to separate insoluble solids from liquids.
Example: Separating sand from water using filter paper.
14. What is decantation? Give an example.
Answer:
Decantation is a process of pouring out the liquid after the heavier component settles down.
Example: Separating oil from water.
15. Explain the process of fractional distillation.
Answer:
Fractional distillation is used to separate liquids with different boiling points. Example: Separation of petroleum into diesel, petrol, and kerosene.
16. Why is chromatography used?
Answer:
Chromatography is used to separate colored substances in a mixture. Example: Separating dyes in ink.
17. Define solubility and give an example.
Answer:
Solubility is the maximum amount of solute that dissolves in a solvent at a given temperature. Example: Salt dissolving in water.
18. Why is water called a universal solvent?
Answer:
Because it can dissolve many substances, like salt, sugar, and gases.
19. How is a saturated solution different from an unsaturated solution?
Answer:
|
Solution Type |
Definition |
Example |
|---|---|---|
|
Saturated |
No more solute can dissolve |
Salt water with excess salt |
|
Unsaturated |
More solute can dissolve |
Normal sugar solution |
20. Why do we need to purify substances?
Answer:
Purification removes impurities to obtain pure substances for medicine, food, and industrial use.
21. What is sedimentation?
Answer:
Sedimentation is the process of heavier particles settling at the bottom of a liquid.
22. Why do particles in a colloid not settle down?
Answer:
Because of small particle size and constant motion due to Brownian movement.
23. Why is air a homogeneous mixture?
Answer:
Because its composition is uniform, containing oxygen, nitrogen, carbon dioxide, and other gases.
24. What is the dispersed phase and dispersion medium in a colloid?
Answer:
Dispersed phase
– Tiny solid or liquid particles.
Dispersion medium
– The substance in which they are distributed.
Example: Milk (
fat particles in water
).
25. What are immiscible liquids? Give an example.
Answer:
Liquids that do not mix together. Example: Oil and water.
26. How can a mixture of water and acetone be separated?
Answer:
By simple distillation, since acetone has a lower boiling point.
27. What are suspensions? Give an example.
Answer:
Suspensions are heterogeneous mixtures where solid particles settle over time. Example: Muddy water.
28. How can we increase the solubility of a solute in water?
Answer:
Increase temperature
Stir the solution
Use a finer solute form
29. What happens when we add salt to water and why?
Answer:
Salt dissolves because water breaks down salt particles due to its polarity.
30. Why is alloy considered a homogeneous mixture?
Answer:
Because its composition is uniform throughout. Example: Brass (Copper + Zinc).
