Exploring Mixtures and Their Separation — Class 9 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 9 Science chapter "Exploring Mixtures and Their Separation" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Exploring Mixtures and Their Separation" — 8 important questions with detailed answers…
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NCERT Solutions for Class 9 Science — Exploring Mixtures and Their Separation. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Exploring Mixtures and Their Separation — All 8 Questions Solved
Q1. Define pure substances and mixtures.
Pure substances have definite composition and fixed physical properties (e.g., water, salt).
Mixtures are combinations of two or more substances that retain individual properties (e.g., salt water, air).
Mixtures can be separated into components.
Q2. What is a solution? Give two examples.
A solution is a homogeneous mixture where one substance (solute) dissolves completely in another (solvent).
Examples: salt water, sugar solution, salt dissolved in alcohol.
Properties: transparent, particles not visible even under microscope, no precipitation on standing.
Q3. Define suspension and colloid with examples.
Suspension: heterogeneous mixture where particles settle on standing (e.g., chalk powder in water, sand in water)
Colloid: mixture where particles are intermediate in size; appear homogeneous but scatter light (e.g., milk, starch solution, paint)
Q4. Compare solutions, suspensions, and colloids.
Solutions: homogeneous, particles <1 nm, transparent, no settling, pass through filter
Colloids: appear homogeneous, particles 1-100 nm, scatter light (Tyndall), no settling, pass through filter
Suspensions: heterogeneous, particles >100 nm, opaque, settle out, blocked by filter
Q5. What is the Tyndall effect?
The Tyndall effect is the scattering of light by colloidal particles. When light passes through a colloid, the path of the light beam becomes visible because colloidal particles scatter the light in all directions.
Q6. Name four separation techniques for mixtures.
1. Filtration - separates insoluble solids from liquids
2. Evaporation - separates solute from solvent by heating
3. Distillation - separates volatile liquid from non-volatile solute
4. Chromatography - separates components based on differential movement
Others: decantation, sublimation, magnetic separation
Q7. Describe the process of distillation.
Distillation separates a volatile liquid from a non-volatile solute by heating the mixture. The volatile liquid evaporates, then the vapor is condensed back to liquid in a separate container, leaving the solute behind.
Q8. How is fractional distillation used in petroleum refining?
Crude oil is heated and vapors rise through a fractionating column with a temperature gradient. Different hydrocarbons condense at different heights based on boiling points: lighter hydrocarbons go higher, heavier ones condense lower, producing petrol, diesel, kerosene, etc.
Exploring Mixtures and Their Separation — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Which of the following is an example of a homogeneous mixture?
- A. Sand and water
- B. Oil and water
- C. Sugar solution
- D. Iron filings and sulfur
Answer: C. Sugar solution — A homogeneous mixture has a uniform composition throughout, meaning its components are evenly distributed. Sugar dissolved in water forms a solution where the sugar particles are uniformly spread.
MCQ 2. A solution is a homogeneous mixture of two or more components. Which of the following statements about a solution is INCORRECT?
- A. The particles of a solution are smaller than 1 nm in diameter.
- B. A solution does not scatter a beam of light passing through it.
- C. The components of a solution can be separated by filtration.
- D. Solutions are stable, meaning the solute particles do not settle down when left undisturbed.
Answer: C. The components of a solution can be separated by filtration. — The particles in a true solution are too small to be separated by filtration. Filtration is effective for separating insoluble solids from liquids in heterogeneous mixtures like suspensions.
MCQ 3. To separate a mixture of acetone and water, which have boiling points of 56°C and 100°C respectively, which separation technique would be most appropriate?
- A. Simple distillation
- B. Fractional distillation
- C. Evaporation
- D. Decantation
Answer: B. Fractional distillation — Fractional distillation is used to separate two miscible liquids with a difference in their boiling points of less than 25 K (25°C). Acetone and water are miscible liquids with boiling points close enough for fractional distillation to be effective.
MCQ 4. The Tyndall effect is observed in:
- A. True solutions
- B. Suspensions
- C. Colloidal solutions
- D. Both suspensions and true solutions
Answer: C. Colloidal solutions — The Tyndall effect is the scattering of a beam of light by the particles in a colloid, making the path of light visible. Particles in true solutions are too small, and particles in suspensions are too large and settle down quickly.
MCQ 5. Which method is generally used to separate insoluble solid impurities from a liquid?
- A. Evaporation
- B. Filtration
- C. Distillation
- D. Centrifugation
Answer: B. Filtration — Filtration is a common method used to separate insoluble solids from liquids by passing the mixture through a filter medium that retains the solid particles.
MCQ 6. Which principle is primarily involved in the separation of different colours in an ink using paper chromatography?
- A. Difference in boiling points
- B. Difference in density
- C. Difference in solubility and adsorption
- D. Difference in magnetic properties
Answer: C. Difference in solubility and adsorption — Paper chromatography separates components based on their differing solubilities in the solvent (mobile phase) and their differing adsorption affinities to the paper (stationary phase).
MCQ 7. Air is a mixture of various gases. How are these gases separated from liquid air?
- A. Simple distillation
- B. Evaporation
- C. Fractional distillation
- D. Centrifugation
Answer: C. Fractional distillation — The components of air (like nitrogen, oxygen, argon) are gases with different boiling points. To separate them from liquid air, fractional distillation is employed, where each gas vaporizes at its specific boiling point.
MCQ 8. Which of the following applications does NOT use the principle of centrifugation?
- A. Separating cream from milk
- B. Separating fine mud particles from water
- C. Drying clothes in a washing machine
- D. Separating different pigments from flower petals
Answer: D. Separating different pigments from flower petals — Centrifugation is used to separate dense particles from a liquid using rapid rotation, as seen in milk separators and washing machines. Separating pigments from flower petals typically uses chromatography or solvent extraction.
MCQ 9. Which of the following is a mixture?
- A. Water
- B. Salt
- C. Air
- D. Carbon dioxide
Answer: C. Air — Air is a mixture of several gases like nitrogen, oxygen, carbon dioxide, etc., that are not chemically combined. Water, salt, and carbon dioxide are compounds.
MCQ 10. Which statement is TRUE for a suspension?
- A. It is a homogeneous mixture.
- B. Its particles are invisible to the naked eye.
- C. Its particles settle down when left undisturbed.
- D. It does not scatter a beam of light.
Answer: C. Its particles settle down when left undisturbed. — A suspension is a heterogeneous mixture where solid particles are dispersed in a liquid. These particles are large enough to be seen with the naked eye and will eventually settle down due to gravity.
MCQ 11. To separate a mixture of kerosene oil and water, which are immiscible liquids, what apparatus would be most suitable?
- A. Distillation flask
- B. Separating funnel
- C. Filter paper
- D. Centrifuge
Answer: B. Separating funnel — A separating funnel is specifically designed to separate immiscible liquids that form distinct layers based on their densities. Kerosene oil floats on water, forming two layers.
MCQ 12. Which of the following substances sublimes on heating?
- A. Common salt
- B. Sugar
- C. Naphthalene
- D. Sand
Answer: C. Naphthalene — Naphthalene is a substance that undergoes sublimation, meaning it directly changes from a solid to a gaseous state without passing through the liquid state upon heating.
MCQ 13. In a sugar solution, which component is the solute?
- A. Water
- B. Sugar
- C. Both sugar and water
- D. Neither sugar nor water
Answer: B. Sugar — In a solution, the solute is the component present in a lesser amount and that dissolves in the solvent. Here, sugar dissolves in water, making sugar the solute.
MCQ 14. Why is crystallization considered a better technique than simple evaporation for purifying solids?
- A. It produces larger crystals.
- B. It removes soluble impurities more effectively.
- C. It can remove impurities like dust that might char on heating.
- D. All of the above.
Answer: D. All of the above. — Crystallization is better because it yields pure solid crystals, can remove soluble impurities (like those that remain after evaporation), and prevents decomposition or charring of heat-sensitive substances during direct heating. It also often produces larger, purer crystals.
MCQ 15. Which separation technique would be best suited to separate a mixture of iron filings and sulphur powder?
- A. Filtration
- B. Evaporation
- C. Magnetic separation
- D. Hand-picking
Answer: C. Magnetic separation — Iron is a magnetic substance, while sulphur is non-magnetic. Therefore, a magnet can be used to attract and separate the iron filings from the sulphur powder.
MCQ 16. A major difference between a true solution and a suspension is that in a true solution, the particles are:
- A. Visible to the naked eye
- B. Too small to be seen and do not settle
- C. Large and scatter light
- D. Always settle down after some time
Answer: B. Too small to be seen and do not settle — Particles in a true solution are extremely small (less than 1 nm), making them invisible and preventing them from settling down.
MCQ 17. Which property is NOT characteristic of a colloidal solution?
- A. Heterogeneous in nature
- B. Shows Tyndall effect
- C. Particles settle down on standing
- D. Particles can be seen with an ultramicroscope
Answer: C. Particles settle down on standing — Colloidal particles are stable and do not settle down when left undisturbed, distinguishing them from suspensions. They are heterogeneous, show Tyndall effect, and can be observed with an ultramicroscope.
MCQ 18. You have a mixture of common salt (sodium chloride) and ammonium chloride. How would you separate these two components?
- A. Dissolve in water and filter
- B. Fractional distillation
- C. Sublimation
- D. Hand-picking
Answer: C. Sublimation — Ammonium chloride sublimes on heating, meaning it directly converts from solid to gas. Common salt (sodium chloride) does not sublime. Therefore, heating the mixture will cause ammonium chloride to sublime and separate, leaving the salt behind.
MCQ 19. In paper chromatography, the component that is more soluble in the solvent and less adsorbed by the stationary phase will:
- A. Travel a shorter distance on the paper
- B. Travel a longer distance on the paper
- C. Not move from the starting line
- D. Evaporate quickly
Answer: B. Travel a longer distance on the paper — Components that are more soluble in the mobile phase (solvent) and have weaker interactions with the stationary phase (paper) will travel further up the chromatogram.
MCQ 20. In a solution of iodine in alcohol (tincture of iodine), which is the solvent?
- A. Iodine
- B. Alcohol
- C. Both
- D. Water
Answer: B. Alcohol — Alcohol is the solvent because it is present in a larger quantity and dissolves the iodine to form the tincture.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.