Class 9 Science Important Questions and Answers: Exploring Mixtures and Their Separation Techniques
Premium NCERT, Board Exam, Exemplar and Olympiad-level question answers for the 2026 CBSE syllabus. This chapter focuses only on mixtures, their types and separation techniques.
Short Introduction
Mixtures are found everywhere in daily life, such as salt solution, muddy water, milk, air, ink and fruit juice. In this chapter, students learn how to identify different types of mixtures and select suitable physical methods to separate their components.
Syllabus focus: This post does not cover elements, compounds, metals and non-metals.
Chapter Overview
1. Mixtures
A mixture contains two or more substances mixed in any proportion.
2. Types of Mixtures
Mixtures may be homogeneous or heterogeneous depending on uniformity.
3. Solutions
A solution is a uniform mixture of solute and solvent.
4. Suspensions
A suspension has large particles that settle on standing.
5. Colloids
A colloid has very small particles that show the Tyndall effect.
6. Separation Techniques
Filtration, evaporation, crystallisation, distillation, chromatography, centrifugation and more.
Important Keywords
Important Very Short Answer Questions
Q1. What is a mixture?
Answer: A mixture is formed when two or more substances are mixed in any proportion without changing their individual properties.
Q2. Give two examples of mixtures.
Answer: Salt solution and muddy water are two examples of mixtures.
Q3. What is a homogeneous mixture?
Answer: A homogeneous mixture has uniform composition throughout. Example: sugar solution.
Q4. What is a heterogeneous mixture?
Answer: A heterogeneous mixture does not have uniform composition throughout. Example: sand in water.
Q5. What is a solute?
Answer: The substance that dissolves in a solvent is called a solute. Example: salt in salt solution.
Q6. What is a solvent?
Answer: The substance in which a solute dissolves is called a solvent. Example: water in salt solution.
Q7. What is the Tyndall effect?
Answer: The scattering of light by colloidal particles is called the Tyndall effect.
Q8. Name the method used to separate cream from milk.
Answer: Centrifugation is used to separate cream from milk.
Q9. Name the method used to separate salt from salt solution.
Answer: Evaporation can be used to separate salt from salt solution.
Q10. Name the method used to separate dyes from ink.
Answer: Chromatography is used to separate dyes from ink.
Short Answer Questions
Q1. Differentiate between homogeneous and heterogeneous mixtures.
Answer:
| Homogeneous Mixture | Heterogeneous Mixture |
|---|---|
| It has uniform composition throughout. | It does not have uniform composition throughout. |
| Components are not visibly separate. | Components may be visibly separate. |
| Example: salt solution. | Example: muddy water. |
Q2. Write three properties of a true solution.
Answer:
- A true solution is homogeneous.
- Its particles are very small and cannot be seen with naked eyes.
- It does not show the Tyndall effect.
- Solute particles do not settle down on standing.
Q3. Write three properties of a suspension.
Answer:
- A suspension is a heterogeneous mixture.
- Its particles are large enough to be seen.
- Particles settle down when left undisturbed.
- It can be separated by filtration.
Q4. Why is milk considered a colloid?
Answer: Milk is considered a colloid because its particles are small, do not settle down on standing and scatter light.
Q5. Why can a mixture be separated by physical methods?
Answer: A mixture can be separated by physical methods because its components retain their individual properties and are not permanently changed during mixing.
Q6. What is crystallisation? Give one use.
Answer: Crystallisation is a method used to obtain pure crystals from a solution. It is used to obtain pure salt or sugar crystals.
Q7. How is filtration different from evaporation?
Answer:
- Filtration: Used to separate an insoluble solid from a liquid.
- Evaporation: Used to separate a dissolved solid from a liquid by heating.
- Example of filtration: sand from water.
- Example of evaporation: salt from salt solution.
Q8. What is chromatography?
Answer: Chromatography is a technique used to separate different coloured components of a mixture, such as dyes in ink.
Long Answer Questions
Q1. Explain the differences between solution, suspension and colloid.
Answer:
| Property | Solution | Suspension | Colloid |
|---|---|---|---|
| Nature | Homogeneous | Heterogeneous | Appears homogeneous but is heterogeneous |
| Particle size | Very small | Large | Intermediate |
| Visibility | Particles not visible | Particles may be visible | Particles not visible to naked eyes |
| Settling | Do not settle | Settle on standing | Do not settle |
| Tyndall effect | No | May show due to large particles | Yes |
| Example | Salt solution | Muddy water | Milk |
Q2. Describe any five separation techniques with examples.
Answer:
- Filtration: Separates insoluble solid from liquid. Example: sand from water.
- Evaporation: Separates dissolved solid from liquid. Example: salt from salt solution.
- Crystallisation: Obtains pure crystals from a solution. Example: sugar crystals.
- Distillation: Separates a liquid from a solution using boiling and condensation. Example: pure water from salt solution.
- Chromatography: Separates coloured components. Example: dyes in ink.
Q3. How will you separate a mixture of sand, salt and water?
Answer:
- First, filter the mixture.
- Sand remains on the filter paper as residue.
- Salt solution passes through as filtrate.
- Heat the filtrate to evaporate water.
- Salt is left behind after evaporation.
Q4. Explain the principle and use of a separating funnel.
Answer:
- A separating funnel is used to separate two immiscible liquids.
- It works on the principle of difference in density.
- The heavier liquid forms the lower layer.
- The lighter liquid forms the upper layer.
- Example: oil and water can be separated using a separating funnel.
Q5. What is centrifugation? Write its principle and uses.
Answer:
- Centrifugation is a method used to separate suspended particles from a liquid by rapid spinning.
- It works on the principle that denser particles move outward faster during spinning.
- It is used to separate cream from milk.
- It is used in laboratories to separate particles from blood samples.
- It is useful when particles are too small for ordinary filtration.
Case-Study Based Questions
Case Study 1: Muddy Water
A student takes muddy water in a beaker. After some time, heavier mud particles settle at the bottom. The clear water above is carefully poured into another container. Later, the remaining liquid is passed through filter paper.
Q1. Which process causes mud particles to settle down?
Answer: Sedimentation.
Q2. What is the process of pouring clear liquid without disturbing the settled particles called?
Answer: Decantation.
Q3. Which process uses filter paper to remove insoluble particles?
Answer: Filtration.
Q4. Is muddy water homogeneous or heterogeneous?
Answer: Muddy water is a heterogeneous mixture.
Case Study 2: Ink on Paper
A student places a small spot of black ink on filter paper and dips the lower end of the paper in water. After some time, different coloured bands appear on the paper.
Q1. Which separation technique is used here?
Answer: Paper chromatography.
Q2. What does this activity show?
Answer: It shows that black ink is a mixture of different coloured dyes.
Q3. Why do different colours travel different distances?
Answer: Different dyes have different solubility and attraction towards the paper.
Q4. Write one use of chromatography.
Answer: It is used to separate colours in dyes, inks and pigments.
Assertion-Reason Questions
Choose the correct option:
A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. Assertion is true but Reason is false.
D. Assertion is false but Reason is true.
Q1. Assertion: A solution does not show the Tyndall effect.
Reason: Particles of a true solution are very small.
Answer: A. Both are true and Reason correctly explains Assertion.
Q2. Assertion: Suspensions are stable mixtures.
Reason: Particles of a suspension settle down on standing.
Answer: D. Assertion is false but Reason is true.
Q3. Assertion: A separating funnel can separate oil and water.
Reason: Oil and water are immiscible liquids with different densities.
Answer: A. Both are true and Reason correctly explains Assertion.
Q4. Assertion: Chromatography can separate dyes present in ink.
Reason: Different dyes may have different solubility in the same solvent.
Answer: A. Both are true and Reason correctly explains Assertion.
Q5. Assertion: Salt can be separated from salt solution by filtration.
Reason: Salt dissolves completely in water.
Answer: D. Assertion is false but Reason is true.
Exam Tips
- Write examples with every separation technique.
- Do not confuse solution, suspension and colloid.
- Use NCERT keywords such as solute, solvent, filtrate, residue, Tyndall effect and immiscible liquids.
- For difference-based questions, use a table format.
- In case-study questions, identify the mixture first and then choose the separation method.
- For concentration numericals, write the formula before substituting values.
Quick Revision Box
Solution
Uniform mixture of solute and solvent.
Suspension
Large particles settle on standing.
Colloid
Shows Tyndall effect and particles do not settle.
Filtration
Separates insoluble solid from liquid.
Evaporation
Separates dissolved solid from solution.
Distillation
Separates liquid using boiling and condensation.
Important Formula for Concentration
Mass by mass percentage:
Concentration = Mass of solute ÷ Mass of solution × 100
Mass by volume percentage:
Concentration = Mass of solute ÷ Volume of solution × 100
Example: A solution contains 10 g salt in 90 g water. Find the concentration by mass percentage.
Answer: Mass of solute = 10 g
Mass of solution = 10 g + 90 g = 100 g
Concentration = 10 ÷ 100 × 100 = 10%
FAQ Section
What is the main focus of this chapter?
The main focus is on mixtures, their types, properties and separation techniques.
Does this chapter include elements, compounds, metals and non-metals?
No. This post is prepared according to the stated 2026 scope and avoids elements, compounds, metals and non-metals.
Which separation technique is most important for exams?
Filtration, evaporation, crystallisation, distillation, chromatography, centrifugation and separating funnel are important.
What is the difference between filtrate and residue?
The liquid that passes through filter paper is called filtrate. The solid left on the filter paper is called residue.
Why does a colloid show the Tyndall effect?
A colloid shows the Tyndall effect because its particles scatter light.
Which method is used to separate oil and water?
A separating funnel is used to separate oil and water.
Which method is used to obtain salt from seawater?
Evaporation is commonly used to obtain salt from seawater.
How should I answer difference questions in board exams?
Use a table, write clear points and include examples wherever possible.
Final Conclusion
Exploring mixtures and their separation techniques is a scoring chapter if students understand the basic properties of solutions, suspensions and colloids. Learn the principle behind each separation method and connect it with daily-life examples. This will help in NCERT questions, CBSE board exams, Exemplar questions and Olympiad-level reasoning.
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