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Practice Class 9 Science Chapter 2 – Is Matter Around Us Pure? with 5 NCERT-based MCQs on colloids, dispersed particles, dispersion medium, Tyndall effect, light scattering and the properties of colloidal mixtures.
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Chapter Information
Subject: Science
Class: 9
Chapter: Is Matter Around Us Pure?
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 5
Difficulty Level: Moderate
Based On: NCERT Syllabus
Introduction
Not all mixtures can be classified simply as true solutions or suspensions. Colloids have properties that lie between those of true solutions and suspensions.
A colloid consists of particles of one substance dispersed throughout another substance. The particles are small enough to remain dispersed for a long time but large enough to scatter light.
This Practice Set 5 focuses on the important characteristics of colloids, dispersed phase, dispersion medium and the Tyndall effect.
What You Will Learn
✔ Meaning of a colloid
✔ Dispersed phase
✔ Dispersion medium
✔ Tyndall effect
✔ Scattering of light
✔ Stability of colloids
✔ Difference between colloids and true solutions
✔ Common examples of colloids
Why This Topic Is Important
Colloids are commonly found in everyday life. Examples include milk, fog, smoke and starch solution.
Understanding colloids helps students distinguish them from true solutions and suspensions. The Tyndall effect is especially important because it provides a useful way to identify the scattering of light by colloidal particles.
These concepts are frequently useful in conceptual questions and MCQs.
5 MCQs with Answers and Detailed Solutions
Q1. Which of the following is an example of a colloid?
A) Salt solution
B) Sugar solution
C) Milk
D) Copper
Answer: C) Milk
Detailed Solution
Milk is a common example of a colloid. It contains tiny droplets of fat and other components dispersed throughout water.
The dispersed particles are small enough to remain distributed for a long time but can scatter light.
Salt solution and sugar solution are true solutions, while copper is a pure substance.
Exam Tip
Remember milk → colloid as an important everyday example.
Q2. The component of a colloid that is present in the form of small particles is called:
A) Dispersion medium
B) Dispersed phase
C) Solvent only
D) Residue
Answer: B) Dispersed phase
Detailed Solution
A colloid has two main components:
- Dispersed phase: The substance present as very small particles.
- Dispersion medium: The substance throughout which the dispersed particles are distributed.
Therefore, the component present as small particles is called the dispersed phase.
Exam Tip
Remember: Dispersed phase = particles being distributed.
Q3. Which phenomenon is responsible for the visibility of the path of a beam of light through a colloid?
A) Filtration
B) Sedimentation
C) Tyndall effect
D) Crystallisation
Answer: C) Tyndall effect
Detailed Solution
The Tyndall effect is the scattering of light by particles present in a colloid.
When a beam of light passes through a colloidal mixture, the colloidal particles scatter the light, making the path of the beam visible under suitable conditions.
This phenomenon helps distinguish colloids from true solutions.
Exam Tip
Tyndall effect = scattering of light by colloidal particles.
Q4. Which of the following is a property of a colloid?
A) Its particles always settle down immediately.
B) Its particles are large enough to be easily separated by ordinary filtration.
C) Its particles can scatter light.
D) It always has a fixed composition.
Answer: C) Its particles can scatter light.
Detailed Solution
Colloidal particles are sufficiently large to scatter light, producing the Tyndall effect.
However, they are small enough to remain dispersed for a considerable period and generally do not settle down like the particles of a suspension.
Therefore, the ability to scatter light is an important property of colloids.
Exam Tip
For colloids, remember scattering of light + no rapid settling.
Q5. Which pair correctly represents a colloid and its dispersion medium?
A) Milk – water
B) Salt solution – salt
C) Sugar solution – sugar
D) Copper – air
Answer: A) Milk – water
Detailed Solution
In milk, tiny fat droplets and other components are dispersed throughout a water-based medium.
Therefore, milk is a colloid in which the water acts as the dispersion medium.
The other options do not correctly represent the components of a colloid.
Exam Tip
In a colloid, identify the medium in which the dispersed particles are distributed as the dispersion medium.
Important Formulas & Concepts
This topic does not involve a major mathematical formula. The following concepts are important.
1. Colloid
A colloid is a mixture in which particles of one substance are dispersed throughout another substance.
2. Dispersed Phase
The component present as small particles in a colloid is called the dispersed phase.
3. Dispersion Medium
The component throughout which the dispersed particles are distributed is called the dispersion medium.
4. Tyndall Effect
The scattering of light by colloidal particles is called the Tyndall effect.
5. Stability of Colloids
Colloidal particles generally remain dispersed and do not settle down rapidly under ordinary conditions.
6. Examples of Colloids
Common examples include:
- Milk
- Fog
- Smoke
- Starch solution
Related Practice Questions
Q1. What is a colloid?
Q2. What is meant by dispersed phase?
Q3. What is dispersion medium?
Q4. What is the Tyndall effect?
Q5. Give two examples of colloids.
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which of the following is a colloid?
A) Salt solution
B) Milk
C) Copper
D) Distilled water
Q2. The particles distributed throughout a colloid form the:
A) Dispersion medium
B) Dispersed phase
C) Solvent
D) Residue
Q3. The scattering of light by colloidal particles is called:
A) Sedimentation
B) Filtration
C) Tyndall effect
D) Sublimation
Q4. Which of the following can show the Tyndall effect?
A) True solution
B) Colloid
C) Pure substance only
D) Element only
Q5. In a colloid, the substance throughout which particles are distributed is called:
A) Dispersed phase
B) Dispersion medium
C) Solute only
D) Residue
Exam Tips
✔ Learn the difference between dispersed phase and dispersion medium.
✔ Remember that Tyndall effect is caused by scattering of light.
✔ Learn common examples such as milk, fog and smoke.
✔ Do not confuse colloids with true solutions.
✔ Remember that colloidal particles generally do not settle down rapidly.
Quick Revision Notes
✔ Colloid: Mixture containing particles dispersed throughout another medium.
✔ Dispersed phase: Substance present as small dispersed particles.
✔ Dispersion medium: Substance throughout which the particles are distributed.
✔ Tyndall effect: Scattering of light by colloidal particles.
✔ Milk: Common example of a colloid.
✔ Fog: Aerosol-type colloid.
✔ Smoke: Aerosol-type colloid.
✔ Colloidal particles generally remain dispersed for a long time.
Common Mistakes Students Make
❌ Confusing dispersed phase with dispersion medium.
❌ Thinking the Tyndall effect is caused by absorption of light.
❌ Assuming every transparent solution shows the Tyndall effect.
❌ Confusing a colloid with a suspension.
❌ Thinking colloidal particles always settle down quickly.
❌ Forgetting that milk is a common example of a colloid.
Key Takeaways
✔ Colloids are mixtures with dispersed particles.
✔ The dispersed phase consists of the particles being distributed.
✔ The dispersion medium is the medium throughout which the particles are distributed.
✔ Colloidal particles can scatter light.
✔ The scattering of light by colloidal particles is called the Tyndall effect.
✔ Milk, fog and smoke are common examples of colloids.
✔ Colloidal particles generally remain dispersed and do not settle rapidly.
FAQs
Q. What is a colloid?
Answer:
A colloid is a mixture in which particles of one substance are dispersed throughout another substance.
Q. What is the dispersed phase?
Answer:
The dispersed phase is the component present as small particles distributed throughout the dispersion medium.
Q. What is a dispersion medium?
Answer:
The dispersion medium is the component throughout which the dispersed particles are distributed.
Q. What is the Tyndall effect?
Answer:
The Tyndall effect is the scattering of light by colloidal particles.
Q. Give examples of colloids.
Answer:
Milk, fog and smoke are common examples of colloids.
Q. Why do colloids show the Tyndall effect?
Answer:
Colloidal particles are large enough to scatter light, so the path of a light beam can become visible when it passes through a colloid.
Conclusion
Class 9 Science Chapter 2 – Is Matter Around Us Pure? focuses on colloids, dispersed phase, dispersion medium and the Tyndall effect.
Understanding these concepts helps students distinguish colloids from true solutions and suspensions. These properties are important for answering conceptual and application-based questions from the chapter.
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