Students can use NCERT Class 9 Advanced Science Solutions Chapter 8 Mixtures and their Separation Question Answer to understand complex concepts with ease.
Mixtures and their Separation Class 9 Questions and Answers
Mixtures and their Separation Question Answer Class 9
Check Your Understanding
Question 1.
What is chromatography? Mention its two main phases.
Answer:
Chromatography is a technique used to separate the components of a mixture based on their different rates of movement.
Two main phases of chromatography are as follows:
- Stationary Phase
- Mobile Phase
Question 2.
Who discovered chromatography and in which year?
Answer:
Chromatography was discovered by Mikhail Tswett in the year 1906. He used this technique to separate plant pigments such as chlorophyll, which is how chromatography got its name (“’chroma”‘ means colour).
Question 3.
What is meant by stationary phase and mobile phase?
Answer:
Stationary Phase: It is the substance that remains fixed in place and does not move.
Example: Silica gel, alumina, or paper.
Mobile Phase: It is the substance that moves through the stationary phase and carries the mixture along.
Example: a liquid solvent or gas.
Question 4.
Name two common adsorbents used in column chromatography.
Answer:
Two common adsorbents used in column chromatography are Silica gel and Alumina (Aluminium oxide)
Question 5.
What is an eluent in column chromatography?
Answer:
The eluent in column chromatography is the liquid solvent that flows through the column and carries the components of the mixture along.
Question 6.
Why do different substances move at different speeds in column chromatography?
Answer:
Different substances move at different speeds because they have different affinities towards the stationary phase and the mobile phase. Substances that are more strongly attracted to the stationary phase move more slowly, while those that are more soluble in the mobile phase move faster.
Question 7.
What is fractional distillation?
Answer:
Fractional distillation is a method used to separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K.
Question 8.
When is fractional distillation preferred over simple distillation?
Answer:
Fractional distillation is used when there are small differences in the boiling points of a mixture.
Question 9.
What is the role of the fractionating column?
Answer:
It provides a large surface area for repeated condensation and vaporisation.
Question 10.
In column chromatography, a mixture of two compounds, A and B, is separated. A comes out first. What can you say about its interaction with the stationary phase?
Answer:
Substance A has less attraction towards the stationary phase (or more solubility in the mobile phase), so it moves faster.
Question 11.
A mixture of ethanol (b.p. 78 °C) and water (b.p. 100 °C) is to be separated. Which method will you use and why?
Answer:
As the difference in boiling points is relatively low. Hence, the method of separation to be used is fractional distillation.
Question 12.
Explain why repeated condensation and vaporisation improve separation in fractional distillation.
Answer:
It increases the purity of vapours by enriching them in the lower boiling component, leading to better separation.
Question 13.
In a fractional distillation column, why does temperature decrease from bottom to top?
Answer:
The bottom is heated strongly, while the top is cooler, creating a temperature gradient needed for condensation.
Question 14.
Why is simple distillation not suitable for separating liquids with close boiling points?
Answer:
Simple distillation is not suitable for close boiling points because it does not provide repeated vaporisation- condensation, so separation is incomplete.
Question 15.
Assertion: In chromatography, separation occurs due to difference in boiling points.
Reason: Components move at different speeds in the column.
(A) Assertion and reason, both are correct, and reason is the correct explanation of the assertion.
(B) Assertion and reason, both are correct, but reason is not the correct explanation of the assertion.
(C) Assertion is correct, but reason is a wrong statement.
(D) Assertion is wrong, but the reason is a correct state¬ment.
Answer:
Option (D) is correct,
Explanation: Chromatography does not depend on boiling points. It is based on the difference in the affinity of substances for the stationary and mobile phases. Because of this difference, components move at different speeds, which leads to separation.
Question 16.
Assertion: Fractional distillation gives better separation than simple distillation.
Reason: It involves repeated condensation and vaporisation.
(A) Assertion and reason, both are correct, and reason is the correct explanation of the assertion.
(B) Assertion and reason, both are correct, but reason is not the correct explanation of the assertion.
(C) Assertion is correct, but reason is a wrong statement.
(D) Assertion is wrong, but the reason is a correct statement.
Answer:
Option (A) is correct.
Explanation: Fractional distillation uses a fractionating column, where vapours repeatedly condense and re-vaporise. This process makes the vapours richer in the lower-boiling component, resulting in better separation than simple distillation.
Question 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
Answer:
Option (B) is correct.
Explanation: Fractional distillation separates liquids based on the difference in their boiling points. The liquid with a lower boiling point vapourises first, rises up in the column, and gets collected earlier than the one with a higher boiling point.
Question 18.
What is the main purpose of the ‘fractionating column’ in fractional distillation?
(A) To heat the mixture faster.
(B) To cool the vapours at a fast rate.
(C) To provide more surface area for vapours.
(D) To let the vapours of two liquids mix properly
Answer:
Option (C) is correct.
Explanation: The fractionating column contains obstacles (like glass beads) that provide a large surface area. This allows repeated condensation and vaporisation, which improves the separation of liquids.
Question 19.
In column chromatography, the solid substance that is filled in the column is called the:
(A) Mobile phase
(B) Solvent
(C) Stationary phase
(D) Mixture
Answer:
Option (C) is correct.
Explanation: The solid (like silica gel or alumina) remains fixed in the column and is called the stationary phase. It interacts differently with each component, helping in separation.
Question 20.
The component of a mixture that moves down the column at a faster rate which is:
(A) most attracted to the stationary phase.
(B) having the highest boiling point.
(C) The one most soluble in the mobile phase (solvent).
(D) The one with the largest particle.
Answer:
Option (C) is correct.
Explanation: A component that is more soluble in the mobile phase and less attracted to the stationary phase moves faster through the column. Components strongly attracted to the stationary phase move more slowly.
Mixtures and their Separation Class 9 Extra Questions and Answers
Short Answer Type Questions
Question 1.
Define the term ‘elution1 as applied to column chromatography.
Answer:
The process of extraction of different adsorbed compounds from the column by means of a suitable solvent is called elution.
Question 2.
Why do different substances separate in column chromatography?
Answer:
Different substances have different attractions toward the stationary phase. Some substances move slowly while others move faster with the solvent, causing separation.
Question 3.
What type of mixtures can be separated by chromatography?
Answer:
Chromatography is mainly used to separate mixtures of coloured substances or dissolved components.
Question 4.
Give a brief description of the principles of the column chromatography techniques taking an example in each case.
Answer:
Chromatography is based on the principle of selective distribution of the components of a mixture between two phases, a stationary phase and a moving phase. The stationary phase can be a solid or liquid, while the mobile phase is a liquid or a gas. When the stationary phase is solid the basis is adsorption and when it is a liquid the basis is partition.
For example: Chromatography is generally used for the separation of coloured substances such as plant pigments or dye stuffs.
Question 5.
Can we separate two liquids, A (boiling point 353 K) and B (boiling point 365 K) present in a mixture by simple distillation?
Answer:
No, because in simple distillation, vapours of both the liquids will be formed simultaneously and will condense together in the receiver as the difference between the boiling points is very small. They can be separated by fractional distillation.
Question 6.
Why is a fractionating column used in fractional distillation?
Answer:
A fractionating column is used to provide repeated condensation and vaporisation of liquids. This helps in better separation of liquids having close boiling points.
Question 7.
The fractional distillation method is suitable for separating which type of mixture? Explain with two examples.
Answer:
Fractional distillation is suitable for separating miscible liquids with close boiling points.
Mixtures that can be separated by the fractional distillation method:
- Alcohol and water
- Different fractions of petroleum.
Question 8.
Differentiate between simple distillation and fractional distillation.
Answer:
| Simple Distillation | Fractional Distillation |
| Used for liquids with a large difference in boiling points | Used for liquids with close boiling points |
| No fractionating column is used | A fractionating column is used |
| Separation is less efficient | Separation is more efficient |
Long Answer Type Questions
Question 1.
Define column chromatography. Name the stationary phase and mobile phase used in column chromatography. Mention its two applications.
Answer:
Column chromatography is a technique used to separate and purify components of a mixture. In this method, the mixture passes through a column packed with an adsorbent such as silica gel or alumina, and different substances separate because they move at different speeds.
The stationary phase is usually silica gel or alumina packed inside the column. The mobile phase is a solvent that moves through the column carrying the mixture. Applications of column chromatography:
- It is used for the purification of organic compounds.
- It is used to separate pigments, medicines, and chemicals in laboratories.
Question 2.
Explain how petroleum is refined using fractional distillation.
Answer:
Petroleum refining is carried out using fractional distillation.
- Crude oil is heated strongly in a furnace.
- The vapours enter a tall fractionating tower.
- Different substances condense at different heights according to their boiling points.
- Heavier fractions condense lower in the tower, while lighter fractions condense higher up.
- Useful products such as LPG, petrol, kerosene, diesel, and lubricating oil are collected separately.
Question 3.
Describe the process of separating alcohol and water by fractional distillation.
Answer:
Alcohol and water are miscible liquids with close boiling points.
- The mixture is heated in a distillation flask.
- Alcohol, having lower boiling point, vapourises first.
- Vapours pass through the fractionating column.
- Repeated condensation and vapourisation occur inside the column.
- Alcohol vapours reach the condenser and cool into liquid form.
- Water remains behind due to its higher boiling point.
Case-Based MCQs
I. A student performed an experiment to separate different coloured substances present in a mixture. A glass column packed with silica gel was used. The mixture was poured into the column, and a solvent was allowed to flow through it. Different coloured bands appeared at different positions and were collected separately.
Question 1.
The technique used in the experiment is:
(A) Filtration
(B) Fractional distillation
(C) Column chromatography
(D) Sublimation Q
Answer:
Option (C) is correct.
Explanation: Column chromatography is a separation technique in which different substances move through a column at different speeds and separate into bands.
Question 2.
Silica gel in the column acts as the:
(A) Mobile phase
(B) Solvent
(C) Stationary phase
(D) Condenser
Answer:
Option (C) is correct.
Explanation: Silica gel remains fixed inside the column and helps in separating substances based on their adsorption strength. Therefore, it acts as the stationary phase.
Question 3.
Different substances separate because they:
(A) have different colours
(B) move at different speeds
(C) have same boiling points
(D) dissolve completely 0
Answer:
Option (B) is correct.
Explanation: Different substances have different attractions toward silica gel, so some move faster while others move slowly, leading to separation.
Question 4.
Column chromatography is mainly used for:
(A) Purification of compounds
(B) Separating insoluble solids
(C) Measuring temperature
(D) Heating liquids
Answer:
Option (A) is correct.
Explanation: Column chromatography is widely used in laboratories to separate and purify compounds from mixtures.
Case-Based Subjective Questions
I. In a petroleum refinery, crude oil is heated strongly and converted into vapours. These vapours pass through a tall fractionating column. Different fractions condense at different heights of the column according to their boiling points and are collected separately as LPG, petrol, diesel, and lubricating oil.
Question 1.
Name the process used in the refinery.
Answer:
The process used is fractional distillation.
Question 2.
Why do different fractions condense at different heights?
Answer:
Different fractions have different boiling points, so they condense at different temperatures and heights in the column.
Question 3.
What is the function of the fractionating column?
Answer:
The fractionating column helps in repeated condensation and vapourisation for efficient separation.
Question 4.
Name any two products obtained from petroleum refining.
Answer:
Petrol and diesel.
Mixtures and their Separation Class 9 MCQ
Question 1.
The best and latest technique for isolation, purification, and separation of organic compounds is:
(A) Crystallisation
(B) Distillation
(C) Sublimation
(D) Chromatography
Answer:
Option (D) is correct.
Explanation: Chromatography is a modern, highly effective technique used to separate, identify, and purify components of a mixture. It is widely used in laboratories for organic compounds because it can accurately separate even very small amounts of substances.
Question 2.
Chromatography is used for the purification of:
(A) Solids
(B) liquids
(C) Gases
(D) All of these
Answer:
Option (D) is correct.
Explanation: Chromatography is a versatile separation technique used for the purification of solids, liquids, and gases. It separates components of a mixture based on their different rates of movement through a stationary phase.
Question 3.
What is the process of washing the components of a mixture out of the column by continuously adding the mobile phase called?
(A) Refluxing
(B) Elution
(C) Centrifugation
(D) Sublimation
Answer:
Option (B) is correct.
Explanation: Elution is the process of extracting one material from another by washing with a solvent.
Question 4.
Two miscible liquids with the minimum difference in boiling point are separated by:
(A) Distillation
(B) Fractional distillation
(C) Crystallisation
(D) Chromatography
Answer:
Option (B) is correct.
Explanation: Two miscible liquids with different boiling points are separated by fractional distillation.
Question 5.
The main part used in fractional distillation is:
(A) Condenser
(B) Filter paper
(C) Fractionating column
(D) China dish
Answer:
Option (C) is correct.
Explanation: The fractionating column helps in repeated condensation and vaporisation, improving separation.
Question 6.
Which mixture can be separated by fractional distillation?
(A) Salt and sand
(B) Oil and water
(C) Ethanol and water
(D) Iron and sulphur
Answer:
Option (C) is correct.
Explanation: Ethanol and water are miscible liquids with different boiling points and are separated by fractional distillation.
Assertion-Reason Questions
Directions: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as:
(A) Both Assertion (A) and Reason (R) are true, and Reason (R) is correct explanation of Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(C) Assertion (A).is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.
Question 1.
Assertion (A): Silica gel or alumina is commonly used in column chromatography.
Reason (R): These substances act as the stationary phase.
Answer:
Option (A) is correct.
Explanation: Silica gel and alumina hold substances differently, helping in the separation of mixture components.
Question 2.
Assertion (A): In column chromatography, all substances come out of the column at the same time.
Reason (R): Different substances have different adsorption strengths.
Answer:
Option (D) is correct.
Explanation: Substances do not leave the column together because they move at different speeds due to different adsorption strengths.
Question 3.
Assertion: Refining of petroleum involves fractional distillation.
Reason: Fractional distillation involves repeated distillation.
Answer:
Option (A) is correct.
Explanation: Petroleum contains many liquids with different but close boiling points. Fractional distillation separates these components efficiently through repeated vaporisation and condensation inside the fractionating column. Therefore, it is used in petroleum refining.
Question 4.
Assertion (A): Water and oil can be separated by fractional distillation.
Reason (R): Fractional distillation separates liquids with close boiling points.
Answer:
Option (D) is correct.
Explanation: Only miscible liquids with different boiling points are separated by fractional distillation. Water and oil are immiscible liquids.