Looking for accurate SEBA Class 9 Science Chapter 2 (Is Matter Around Us Pure) textual solutions for the 2026–27 academic year? Access complete step-by-step textbook exercise answers covering mixtures vs pure substances, solutions, suspensions, colloids, concentration calculations, separation techniques, and physical vs chemical changes to score top marks in your exams.
1. What is meant by a substance?
Ans. A substance is a pure form of matter that possesses a uniform composition and identical chemical properties throughout its structure. Examples include water, oxygen, gold, and sugar.
2. List the points of differences between homogeneous and heterogeneous mixtures.
Ans. The key differences between homogeneous and heterogeneous mixtures are:
- A homogeneous mixture appears uniform throughout, whereas a heterogeneous mixture does not look uniform.
- In a homogeneous mixture, the components are evenly mixed, while in a heterogeneous mixture, the components are unevenly distributed.
- The constituent particles of a homogeneous mixture are not visible to the naked eye, whereas the particles in a heterogeneous mixture are often visible.
- A homogeneous mixture cannot be separated easily by simple physical methods, whereas a heterogeneous mixture can be separated relatively easily.
- Sugar dissolved in water is an example of a homogeneous mixture, while sand mixed with water is an example of a heterogeneous mixture.
3. Differentiate between homogeneous and heterogeneous mixtures with examples.
Ans.
| Homogeneous Mixture | Heterogeneous Mixture |
| Maintains a uniform composition throughout its volume | Has a non-uniform composition in different parts |
| Salt solution, lemon juice | Soil, oil mixed with water, sand in water |
4. How are sol, solution and suspension different from each other?
Ans. Solutions, colloidal sols, and suspensions differ across several fundamental properties:
- Nature: A solution is homogeneous in nature, whereas both a colloidal sol and a suspension are heterogeneous in nature.
- Particle size: The particle size in a solution is extremely small, in a colloidal sol it is medium-sized, and in a suspension, the particles are large.
- Tyndall effect: Solutions do not scatter light and thus do not show the Tyndall effect, whereas both colloidal sols and suspensions show the Tyndall effect.
- Settling of particles: Particles do not settle down in solutions or colloidal sols, but they do settle down over time in suspensions.
- Examples: Salt water is an example of a solution, milk and ink are examples of colloidal sols, and muddy water is an example of a suspension.
5. To make a saturated solution, 36 g NaCl is dissolved in 100 g water at 293 K. Find its concentration.
Ans. To calculate the concentration, we first determine the total mass of the solution by adding the mass of the solute (36 g of NaCl) to the mass of the solvent (100 g of water), which gives 136 g. Applying the mass percentage formula:
Mass %=Mass of solutionMass of solute×100
Concentration=13636×100=26.47%≈26.5%
Therefore, the concentration of the sodium chloride solution is 26.5% (mass by mass).
SEBA Class 9 Science Chapter 2 Solutions
6. Classify the following as chemical or physical changes:
Ans.
- Cutting of trees: This is classified as a physical change.
- Melting of butter: This is classified as a physical change.
- Rusting of almirah: This is classified as a chemical change.
- Boiling of water: This is classified as a physical change.
- Passing current through water to form H₂ & O₂: This is classified as a chemical change.
- Dissolving salt in water: This is classified as a physical change.
- Making fruit salad: This is classified as a physical change.
- Burning of paper and wood: This is classified as a chemical change.
7. Try segregating the things around you as pure substances or mixtures.
Ans.
- Pure Substances: Things composed of only one type of particle include gold, oxygen gas, distilled water, sugar, and iron nails.
- Mixtures: Things composed of more than one type of particle include air, sea water, soil, tea, fruit salad, milk (colloid), and steel (an alloy of iron and carbon).
Class 9 Science Chapter 2 Question Answer SEBA 2026-27
Textbook exercise
1. Which separation techniques will you apply for the following?
(a) To separate sodium chloride from its solution in water
Answer: the evaporation technique is used, where water evaporates leaving the salt behind.
(b) To separate ammonium chloride from a mixture of sodium chloride and ammonium chloride
Answer: sublimation is applied because ammonium chloride changes directly into vapor on heating.
(c) To separate small pieces of metal from the engine oil of a car
filtration through a fine filter or centrifugation is used.
(d) To separate different pigments from an extract of flower petals
Answer: chromatography is used.
(e) To separate butter from curd
centrifugation or churning is applied.
(f) To separate oil from water
Answer: a separating funnel is used based on their density differences.
(g) To separate tea leaves from tea
Answer: filtration using a sieve is applied.
(h) To separate iron pins from sand
Answer: magnetic separation is used because iron is attracted to magnets.
(i) To separate wheat grains from husk
Answer: winnowing is applied using wind currents.
(j) To separate fine mud particles suspended in water
Answer: sedimentation and decantation or filtration techniques are used.
Is Matter Around Us Pure Class 9 SEBA Textual Exercise Solutions
2. Write the steps for making tea using scientific terms.
Ans. First, take a measured amount of water in a pan, where the water acts as the solvent. Next, add tea leaves to the water, which contain soluble substances that act as solutes. Heat and boil the mixture to speed up the dissolution rate of the solute, forming a liquid solution known as tea liquor. Then, add milk and sugar into the pan; sugar acts as a soluble solute, while milk forms a colloidal mixture with the solution. Stir the mixture thoroughly until the sugar dissolves completely into the solution. Finally, pass the prepared mixture through a sieve to perform filtration, where the liquid tea obtained is the filtrate and the used tea leaves remaining in the sieve are the residue.
3. Solubility Table Questions
(a) To calculate the mass of potassium nitrate needed to produce a saturated solution in 50 g of water at 313 K, we note that the solubility of KNO3 is 62 g per 100 g of water.
Applying proportional calculation: Mass required = (62 / 100) * 50 = 31 g Therefore, 31 g of potassium nitrate is needed.
(b) When a saturated solution of potassium chloride (KCl) is cooled from 353 K to room temperature (293 K), its solubility decreases from 54 g to 35 g per 100 g of water. Because the extra dissolved salt cannot remain in solution at the lower temperature, solid crystals of potassium chloride will settle out of the solution.
(c) Comparing the solubility values of the given salts at 293 K—potassium nitrate (32 g), sodium chloride (36 g), potassium chloride (35 g), and ammonium chloride (37 g)—ammonium chloride has the highest solubility at 37 g per 100 g of water.
(d) Temperature changes significantly affect solubility, as the solubility of most solid substances in water increases with an increase in temperature. For instance, the solubility of potassium nitrate increases from 32 g at 293 K to 62 g at 313 K.
4. Explain the following with examples:
(a) Saturated Solution: A saturated solution is a chemical solution in which no additional solute can be dissolved at a specific temperature. An example is adding table salt to water continuously until the excess salt stops dissolving and settles at the bottom.
(b) Pure Substance: A pure substance is a form of matter that consists of only one single type of particle with uniform properties throughout. Examples include distilled water, oxygen gas, and pure gold.
(c) Colloid: A colloid is a heterogeneous mixture in which the intermediate-sized particles remain evenly suspended throughout the medium and do not settle down under gravity. Examples include milk, fog, and smoke.
(d) Suspension: A suspension is a heterogeneous mixture containing large solute particles that do not dissolve and eventually settle down at the bottom when left undisturbed. An example is a mixture of mud and water.
5. Classify as homogeneous or heterogeneous mixtures:
Ans. Soda water, vinegar, filtered tea, and air (when free of dust particles) are classified as homogeneous mixtures. On the other hand, wood and soil are classified as heterogeneous mixtures.
SEBA Class 9 Science Chapter 2 Textbook Answers
6. How to confirm that a colourless liquid is pure water?
Ans. To confirm whether a given colourless liquid is pure water, its boiling point and freezing point must be accurately measured at standard atmospheric pressure. Pure water boils at exactly 100°C (373 K) and freezes at 0°C (273 K). If the sample changes state at these exact fixed temperatures, it is confirmed to be pure water.
7. Which of the following materials fall in the category of a “pure substance”?
Ans. Pure substances consist of only one type of constituent particle. Among the listed materials, ice (solid water), iron (element), hydrochloric acid (compound), calcium oxide (compound), and mercury (element) fall into the category of pure substances. Conversely, milk, brick, wood, and air are classified as mixtures.
8. Identify the solutions among the following mixtures.
Ans. A solution is defined as a homogeneous mixture of two or more substances. Among the given options, sea water, air, and soda water are solutions, whereas soil and coal are non-solution heterogeneous mixtures.
9. Which of the following will show “Tyndall effect”?
Ans. The Tyndall effect is the scattering of a light beam caused by colloidal particles. Among the given choices, milk and starch solution show the Tyndall effect because they are colloids, whereas salt solution and copper sulphate solution do not show it because they are true solutions.
10. Classify into elements, compounds and mixtures:
Ans.
- Elements: Sodium, silver, tin, and silicon are pure substances that cannot be broken down further and are classified as elements.
- Compounds: Calcium carbonate, methane, and carbon dioxide are chemical combinations of elements in fixed ratios and are classified as compounds.
- Mixtures: Soil, sugar solution, coal, air, soap, and blood contain multiple non-chemically combined components and are classified as mixtures.
Class 9 Science Chapter 2 Solutions
11. Which of the following are chemical changes?
Ans. A chemical change involves the formation of one or more new substances with different properties. Among the given activities, the growth of a plant, the rusting of iron, the cooking of food, the digestion of food, and the burning of a candle are chemical changes. In contrast, mixing iron filings with sand and the freezing of water are physical changes.
🔬 Updated Solutions Notice: This page features complete, step-by-step SEBA Class 9 Science Chapter 2 (Is Matter Around Us Pure) Textual Exercise Solutions updated for the 2026–27 academic session. All concentration percentage calculations, Tyndall effect explanations, and separation method steps strictly follow the latest revised Assam Board (SEBA) curriculum.
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