CBSE Important Questions Class 9 Science Chapter 2 – Is Matter Around Us Pure

Class 9 Science Chapter 2 Is Matter Around Us Pure is part of the CBSE Class 9 Science syllabus. It explains the difference between a pure substance and a mixture, between homogeneous and heterogeneous mixtures, and between solutions, suspensions and colloids. Students also learn the many ways of separating the components of a mixture, such as filtration, evaporation, sublimation, distillation, fractional distillation, chromatography, centrifugation and magnetic separation.

These CBSE important questions for Class 9 Science Chapter 2 cover choosing the right separation technique for different mixtures, the filtration apparatus with residue and filtrate, the principle of fractional distillation, saturated solutions, pure substances, colloids and suspensions, and alloys. Every question has a clear step-by-step answer in simple English with figures, so students can practise on their own, parents can check the answers, and teachers can use them for class tests.

CBSE Important Questions Class 9 Science Chapter 2 – Is Matter Around Us Pure

Q1. Amit took three unknown substances P, Q and R during an experiment. He noted the following information about these three substances.

Substance Boiling point / °C Solubility (in water)
P 60 Soluble
Q 50 Insoluble
R 95 Soluble

Based on this information, which of the following sets of techniques is correctly used by Amit to separate these substances from their mixtures in water?
(a) P – Separating funnel, Q – Distillation, R – Fractional distillation
(b) P – Evaporation, Q – Distillation, R – Fractional distillation
(c) P – Distillation, Q – Separating funnel, R – Fractional distillation
(d) P – Sublimation, Q – Distillation, R – Fractional distillation

Answer: (c) P – Distillation, Q – Separating funnel, R – Fractional distillation
P dissolves in water and its boiling point (60 °C) is far from that of water, so simple distillation separates it.
Q does not dissolve in water, so the two form separate layers and a separating funnel is used.
R dissolves in water and its boiling point (95 °C) is very close to that of water (100 °C). When the difference is less than 25 °C, fractional distillation is used.

Q2. Which separation technique will you apply for the separation of the following?
(a) Sodium chloride from its solution in water
(b) Ammonium chloride from a mixture of sodium chloride and ammonium chloride
(c) Small pieces of metal in the engine oil of a car
(d) Different pigments from an extract of flower petals
(e) Butter from curd
(f) Oil from water
(g) Tea leaves from tea
(h) Iron pins from sand
(i) Wheat grains from husk
(j) Fine mud particles suspended in water

Answer: (a) Evaporation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Using a separating funnel
(g) Filtration
(h) Magnetic separation
(i) Winnowing
(j) Centrifugation

Q3. The given apparatus shows the separation of soil and water. Identify A and B in this apparatus.
(a) A = Residue, B = Filtrate
(b) A = Residue, B = Distillate
(c) A = Distillate, B = Filtrate
(d) A = Filtrate, B = Residue

Filtration apparatus separating soil from water

Answer: (a) A = Residue, B = Filtrate
The soil cannot pass through the filter paper and stays on it. The solid left on the filter paper is called the residue, which is A. The clear liquid that passes through and collects in the flask below is called the filtrate, which is B.

Q4. The principle behind the fractional distillation technique for separating two liquids is
(a) difference in melting point
(b) difference in boiling point
(c) difference in concentration
(d) difference in solubility

Answer: (b) difference in boiling point
In fractional distillation the mixture is heated. The liquid with the lower boiling point vaporises first, rises through the fractionating column and is condensed and collected separately. This method is used when the boiling points of the two liquids differ by less than 25 °C.

Q5. Explain the following, giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension

Matter divided into pure substances and mixtures, with their types

Answer: (a) Saturated solution: a solution in which no more solute can be dissolved at a given temperature. Example: a soft drink is saturated with carbon dioxide, which is why it gives off bubbles of gas.
(b) Pure substance: a substance that shows the same properties throughout at a given temperature and pressure. Example: distilled water.
(c) Colloid: a heterogeneous mixture in which the particles are bigger than those in a solution but smaller than those in a suspension, and they do not settle down. Examples: milk, smoke, butter.
(d) Suspension: a heterogeneous mixture in which solid particles are spread through a liquid but do not dissolve. The particles are large enough to be seen and they settle down on standing. Examples: chalk powder in water, muddy water.

Q6. Identify the correct statement(s) about alloys.
I: They are mixtures of two or more non-metals.
II: They are mixtures of two or more metalloids.
III: They are mixtures of two or more metals.
IV: They are mixtures of a metal and a non-metal.
(a) I and II
(b) III and IV
(c) Only III
(d) Only I

Answer: (b) III and IV
An alloy is a homogeneous mixture of metals, or of a metal with a non-metal. Brass (copper + zinc) and bronze (copper + tin) are mixtures of two metals, while steel is a mixture of the metal iron with the non-metal carbon. So both III and IV are correct.

Q7. An alloy is
(a) a homogeneous mixture of solids in liquids
(b) a heterogeneous mixture of liquids in solids
(c) a homogeneous mixture of solids in solids
(d) a heterogeneous mixture of liquids in liquids

Answer: (c) a homogeneous mixture of solids in solids
An alloy is made by melting metals together and letting them cool, so the final alloy is a solid in which the components are mixed evenly throughout. That makes it a homogeneous solid-in-solid mixture.

Q8. Rice is soaked in water before cooking to remove dirt, straw and husk if present. This separation technique is called
(a) Threshing
(b) Sedimentation
(c) Decantation
(d) Winnowing

Answer: (b) Sedimentation
When rice is soaked, the heavier dirt and stones settle down at the bottom of the vessel. The settling of heavier insoluble particles is called sedimentation. The water with the light husk floating on it is then poured off, which is decantation.

Q9. During filtration, the pure liquid is obtained as ______ while the insoluble solid is obtained as ______.
(a) Liquid; solid
(b) Filter; filtrate
(c) Filtrate; residue
(d) Residue; filtrate

Answer: (c) Filtrate; residue
The liquid that passes through the filter paper is called the filtrate. The insoluble solid that is left behind on the filter paper is called the residue.

Q10. Select the most appropriate separation technique which can be used to separate a mixture of sand and water.
(a) Hand picking
(b) Filtration
(c) Sieving
(d) Magnetic separation

Answer: (b) Filtration
Sand does not dissolve in water, and its particles are too small to pick up by hand. On pouring the mixture through filter paper, the sand stays as residue and clear water passes through as filtrate. Sieving is for dry solids of different sizes, and magnetic separation works only for magnetic materials.

Q11. Cheese is prepared by curdling of milk. It is separated from the liquid by
(a) magnetic separation
(b) evaporation
(c) filtration
(d) sedimentation

Answer: (c) filtration
After milk curdles, the solid cheese curds are suspended in the liquid whey. Pouring this through a cloth or a strainer holds back the solid curds and lets the whey pass through, which is filtration.

Q12. Match the separation technique in List-I with the mixtures in List-II and select the correct answer using the codes given below.

Separation Technique Mixture
(a) Magnetic separation (p) Mixture of salt and water
(b) Evaporation (q) Mixture of tea leaves and water
(c) Filtration (r) Mixture of chaff and wheat
(d) Sieving (s) Mixture of salt and iron filings

(a) a–q, b–r, c–p, d–s
(b) a–q, b–r, c–s, d–p
(c) a–r, b–p, c–s, d–q
(d) a–s, b–p, c–q, d–r

Answer: (d) a–s, b–p, c–q, d–r
Magnetic separation pulls out the iron filings from salt (s). Evaporation removes the water and leaves the salt behind (p). Filtration holds back the tea leaves from the tea (q). Sieving separates the light chaff from the wheat grains (r).

Related Study Material on Extramarks

Q.1 Complete the table:

Marks:2
Ans

Q.2 Justify the given statements.
a. Epidermal cells absorb water for the plant.
b. Cutin is like sunscreen for a desert plant.
c. Cork consists of dead cells.

Marks:5
Ans

a. Epidermal cells are present in the root and other parts of the plants. Epidermal cells, as part of the roots, help in the absorption of water from the soil.
b. Cutin is the thick waxy coating that is present on the surface of the desert plants. It protects them against the excessive removal of the water from the plant in the presence of sunlight. Similarly, sunscreen protects the human skin from sunlight.
c. The cork cells lose the protoplast on maturity. Therefore, the cells of cork are the dead cells.

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