Class 9 · Advanced ScienceNCERT 2026 Revised Syllabus
Chapter 8: Mixtures and Separation of Mixtures
Science Advanced
Chromatography (stationary and mobile phase), column chromatography, and simple vs fractional distillation with the role of the fractionating column.
Find complete NCERT solutions for Class 9 Advanced Science, Science Advanced Chapter 8. Every question has a clear, step-by-step answer.
Questions(20 questions)
1
What is chromatography? Mention its two main phases.
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Solution:- Chromatography separates components based on their differing rates of movement.
- It uses a stationary phase and a moving mobile phase.Answer: Chromatography separates mixture components using a stationary phase and a moving mobile phase.
2
Who discovered chromatography and in which year?
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Solution:The Russian botanist Mikhail Tswett discovered chromatography in 1906 while studying plant pigments.Answer: Mikhail Tswett, in 1906.
3
What is meant by stationary phase and mobile phase?
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Solution:- Stationary phase: the fixed medium (e.g. silica gel) over which components move.
- Mobile phase: the moving solvent that carries the mixture.Answer: Stationary phase is the fixed medium; mobile phase is the moving solvent.
4
Name two common adsorbents used in column chromatography.
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Solution:Two common adsorbents used in column chromatography are silica gel and alumina.Answer: Silica gel and alumina.
5
What is an eluent in column chromatography?
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Solution:The eluent is the solvent poured through the column, which carries the mixture's components down through the stationary phase.Answer: The eluent is the solvent that carries components down the column.
6
Why do different substances move at different speeds in column chromatography?
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Solution:- Substances have different adsorption tendencies toward the stationary phase.
- More strongly adsorbed components move slower than weakly adsorbed ones.Answer: Different adsorption strengths cause components to move at different speeds.
7
What is fractional distillation?
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Solution:Fractional distillation separates miscible liquids whose boiling points differ by less than 25 °C, using a fractionating column.Answer: Fractional distillation separates miscible liquids with close boiling points using a fractionating column.
8
When is fractional distillation preferred over simple distillation?
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Solution:- Preferred when boiling points differ by less than 25 °C.
- Requires better separation than simple distillation can provide.Answer: Fractional distillation is preferred when boiling points differ by less than 25 °C.
9
What is the role of the fractionating column?
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Solution:- The fractionating column provides extra surface area.
- This allows repeated condensation and vaporisation.
- It improves separation of liquids with close boiling points.Answer: The fractionating column provides extra surface area for repeated condensation and vaporisation.
10
In column chromatography, a mixture of two compounds A and B is separated, and A comes out first. What can you say about its interaction with the stationary phase?
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Solution:- A comes out first (elutes first).
- A is less strongly adsorbed onto the stationary phase.
- It travels faster along with the mobile phase.Answer: Compound A is less strongly adsorbed, so it travels faster and elutes first.
11
A mixture of ethanol (boiling point 78 degrees Celsius) and water (boiling point 100 degrees Celsius) is to be separated. Which method will you use and why?
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Solution:- Boiling point difference
$= 100 - 78 = 22\degree$C, which is less than 25 °C.
- A fractionating column is required for effective separation.Answer: Use fractional distillation, since the boiling point difference is less than 25 °C.12
Explain why repeated condensation and vaporization improve separation in fractional distillation.
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Solution:- Each condensation-vaporisation cycle further enriches the rising vapour with the more volatile component.
- This gradually achieves purer separation as vapour rises through the column.Answer: Repeated cycles enrich the vapour with the more volatile component, giving purer separation.
13
In a fractional distillation column, why does temperature decrease from bottom to top?
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Solution:- More volatile, lower-boiling components rise higher in the column before condensing.
- So the temperature progressively decreases with increasing height.Answer: Temperature decreases from bottom to top because more volatile components rise higher.
14
Why is simple distillation not suitable for separating liquids with close boiling points?
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Solution:- Without a fractionating column, the vapours of both liquids rise together.
- This gives poor separation when boiling points are close.Answer: Without a fractionating column, both vapours rise together giving poor separation.
15
Assertion: In chromatography, separation occurs due to difference in boiling points. Reason: Components move at different speeds in the column.
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Solution:- Assertion (separation due to boiling points) is false.
- Reason (components move at different speeds) is true.
- Chromatography separation is due to differing adsorption or solubility, not boiling points.Answer: (D) Assertion false, reason true.
16
Assertion: Fractional distillation gives better separation than simple distillation. Reason: It involves repeated condensation and vaporization.
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Solution:- Assertion: Fractional distillation gives better separation - correct.
- Reason: It involves repeated condensation and vaporization - correct.
- The reason correctly explains the assertion.Answer: (A) Both assertion and reason are correct, and the reason explains the assertion.
17
Difference in which property forms the basis for separating components in fractional distillation? (a) Solubility (b) Boiling points (c) Particle size (d) Chemical reactivity
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Solution:Fractional distillation separates components based on their boiling points.Answer: (b) Boiling points.
18
What is the main purpose of the fractionating column in fractional distillation? (a) To heat the mixture faster (b) To cool vapours at a fast rate (c) To provide more surface area for vapours (d) To let vapours mix
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Solution:The fractionating column's main purpose is to provide more surface area for vapours.Answer: (c) To provide more surface area for vapours.
19
In column chromatography, the solid substance filled in the column is called the: (a) Mobile phase (b) Solvent (c) Stationary phase (d) Mixture
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Solution:The solid substance filled in the column is the stationary phase.Answer: (c) Stationary phase.
20
Which component of a mixture moves down the column at a faster rate? (a) Most attracted to stationary phase (b) Highest boiling point (c) Most soluble in mobile phase (d) Largest particle
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Solution:The component most soluble in the mobile phase (solvent) moves down the column faster.Answer: (c) The one most soluble in the mobile phase.