Class 9 Science Ch 2 Is Matter Around Us Pure-NCERT Solution

In Class 9 Science Ch 2 Is Matter Around Us Pure-NCERT, students learn about the concept of purity in matter.

The chapter distinguishes between pure substances and mixtures, explaining the properties of homogeneous and heterogeneous mixtures.

It also covers methods of separation like filtration, distillation, and more, helping students understand how different components can be isolated from mixtures. Through real-life examples, the chapter explores solutions, colloids, and suspensions, providing a foundational understanding of matter’s composition.

Class 9 Science Ch 2 Is Matter Around Us Pure-NCERT – Page 1

Question 1. What is meant by a substance?

Answer: A pure substance consists of a single type of particles.

Question 2. List the points of differences between homogeneous and heterogeneous mixtures.
Answer:

Class 9 Science Ch 2 Is Matter Around Us Pure-NCERT– Page 18

Question 1. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:

Question 2. How are sol, solution and suspension different from each other?
Answer:

Question 3. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Answer: Given:

Mass of solute (sodium chloride) = 36 g
Mass of solvent (water) = 100 g
Total mass of solution = 36 g + 100 g = 136 g

Concentration (by mass) = (Mass of solute / Mass of solution) × 100
= (36 / 136) × 100
= 26.47%

Answer:
The concentration of the solution is 26.47% by mass.

Class 9 Science Ch 2 Is Matter Around Us Pure-NCERT– Textbook Page 24

Question 1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?
Answer: A mixture of kerosene and petrol which are miscible with each other can be separated by distillation.
Method

Take a mixture in a distillation flask.
Fit it with a thermometer.
Arrange the apparatus as shown in the figure.
Heat the mixture slowly.
Petrol vaporises first as it has lower boiling point. It condenses in the condenser and is collected from the condenser outlet.
Kerosene is left behind in the distillation flask.

Question 2. Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
Answer: (i) Centrifugation,
(ii) Evaporation,
(iii) Sublimation.

Question 3. What type of mixtures are separated by the technique of crystallisation?
Answer: Crystallisation technique is used to purify solid with some impurities in it. Example: Salt from sea-water.

NCERT Textbook Questions Page 24
Question 2. Classify the following as chemical or physical changes:

cutting of trees,
melting of butter in a pan,
rusting of almirah,
boiling of water to form steam,
passing of electric current, through water and the water breaking down into hydrogen and oxygen gas,
dissolving common salt in water,
making a fruit salad with raw fruits and
burning of paper and wood.

Answer:

Question 3. Try segregating the things around you as pure substances or mixtures
Answer: Pure substances—Water, bread, sugar and gold.
Mixtures—Steel, plastic, paper, talc, milk and air.

Text book

Question 1. Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing 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) Separating funnel
(g) Filtration
(h) Magnetic separation
(i) Winnowing/ sedimentation
(j) Decantation and filtration

Question 2. Write the steps you would use for making tea. Use the words, solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer: 1. Take a cup of water in a container as solvent and heat it.
2. Add sugar in it which is solute. Heat it till all sugar dissolves.
3. You get a solution of water and sugar.
4. Sugar is soluble in water completely.
5. Add half a tea-spoon of tea-leaves, it is insoluble in water.
6. Boil the content, add milk which is also soluble in water, boil again.
7. Filter the tea with the help of strainer, the tea collected in cup is filtrate and the tea leaves collected on the strainer is residue.

Question 3:
Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

Substance Dissolved	283 K	293 K	313 K	333 K	353 K
Potassium nitrate	21	32	62	106	167
Sodium chloride	36	36	36	37	37
Potassium chloride	35	35	40	46	54
Ammonium chloride	24	37	41	55	66

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

Answer:
Solubility of potassium nitrate at 313 K = 62 g per 100 g water.
So, in 50 g of water:
(62 / 100) × 50 = 31 g

Therefore, 31 grams of potassium nitrate are needed.

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.

Answer:
Solubility of potassium chloride at 353 K = 54 g
Solubility at room temperature (approx. 293 K) = 35 g
As the temperature decreases, excess potassium chloride (54 g − 35 g = 19 g) will crystallize out.
Therefore, Pragya will observe that some of the salt settles at the bottom as crystals.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

Answer:
Solubility at 293 K:

Potassium nitrate = 32 g
Sodium chloride = 36 g
Potassium chloride = 35 g
Ammonium chloride = 37 g

Ammonium chloride has the highest solubility (37 g) at 293 K.

(d) What is the effect of change of temperature on the solubility of a salt?

Question 4. Explain the following giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Answer: (a) Saturated solution: In a given solvent when no more solute can dissolve further at a given temperature is called saturated solution.
(b) Pure substance: A pure substance consists of a single type of particles. E.g., gold, silver.
(c) Colloid: A colloid is a solution in which the size of solute particles are bigger than that of true solution. These particles cannot be seen with our naked eyes, they are stable, e.g., ink, blood.
(d) Suspension: It is a heterogeneous mixture in which the solute particles are big enough to settle down, e.g., chalk-water, paints, etc.

Question 5. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air. soil, vinegar, filtered tea.
Answer: Homogeneous: Soda water, vinegar, filtered tea.
Heterogeneous: Wood, air, soil.

Question 6. How would, you confirm that a colourless liquid given to you is pure water?
Answer: By finding the boiling point of a given colourless liquid. If the liquid boils at 100°C at atmospheric pressure, then it is pure water. This is because pure substances have fixed melting and boiling point.

Question 7. Which of the following materials fall in the category of a “pure substance”?
(a) Ice (b) Milk (c) Iron
(d) Hydrochloric acid (e) Calcium oxide (f) Mercury
(g) Back (h) Wood (i) Air.
Answer: Pure substances are: Ice, iron, hydrochloric acid, calcium oxide and mercury.

Question 8. Identify the solutions among the following mixtures.
(a) Soil (b) Sea water
(c) Air (d) Coal
(e) Soda water.
Answer: Solutions are: Sea water soda water and air.

Question 9. Which of the following will show “Tyndall effect”?
(a) Salt solution (b) Milk
(c) Copper sulphate solution (d) Starch solution.
Answer: Milk and starch solution.

Question 10. Classify the following into elements, compounds and mixtures.
(a) Sodium (b) Soil (c) Sugar solution
(d) Silver (e) Calcium carbonate (f) Tin
(g) Silicon (h) Coal (i) Air
(j) Soap (k) Methane (l) Carbon dioxide
(m) Blood
Answer: Elements – Compounds – Mixtures
Sodium – Calcium carbonate – Sugar solution
Silver – Methane – Soil
Tin – Carbon dioxide – Coal
Silicon – Soap – Air ,Blood

Question 11. Which of the following are chemical changes?
(a) Growth of a plant (b) Rusting of iron
(c) Mixing of iron filings and sand (d) Cooking of food
(e) Digestion of food (f) Freezing of water
(g) Burning of a candle.
Answer: Chemical changes are:
(a) Growth of a plant (b) Rusting of iron
(c) Cooking of food (d) Digestion of food
(e) Burning of a candle

EXTRA QUESTIONS

1.What is a pure substance? Explain with examples.

Answer:
A pure substance is a material that consists of only one type of particle. It has uniform composition and properties throughout. Examples include elements like oxygen (O₂) and compounds like water (H₂O). These substances cannot be separated into other materials by physical means.

2. What is a mixture? How is it different from a pure substance?

Answer:
A mixture is a combination of two or more substances that are physically combined, and each substance retains its properties. Unlike pure substances, mixtures can be separated into their components by physical methods like filtration or evaporation. Examples include air (a mixture of gases) and a salad (a mixture of vegetables).

3. Explain homogeneous mixtures with an example.

Answer:
Homogeneous mixtures are those in which the components are uniformly distributed, and the composition is the same throughout. An example is a salt solution in water. In such mixtures, individual components cannot be seen or separated easily.

4. What is a heterogeneous mixture? Give an example.

Answer:
Heterogeneous mixtures are those in which the components are not uniformly distributed, and different substances can be easily distinguished. An example is a mixture of sand and water. The components are not evenly mixed, and you can clearly see and separate them.

5. Define solution. What are its components?

Answer:
A solution is a homogeneous mixture of two or more substances where one substance dissolves in another. The components of a solution are:

Solute: The substance that dissolves (e.g., salt).
Solvent: The substance in which the solute dissolves (e.g., water).

6. Explain the process of filtration. Where is it used?

Answer:
Filtration is a physical method used to separate solid particles from a liquid or gas by passing the mixture through a filter. The solid particles are retained by the filter, and the liquid or gas passes through. It is used in purifying water or separating sand from water.

7. What is distillation? Explain with an example.

Answer:
Distillation is a process used to separate components of a liquid mixture based on their different boiling points. For example, in the distillation of seawater, water is boiled to form steam, which is then condensed back into liquid water, leaving behind impurities like salt.

8. What is the difference between a solution and a suspension?

Answer:
A solution is a homogeneous mixture where the solute completely dissolves in the solvent, and the particles are not visible. A suspension, on the other hand, is a heterogeneous mixture where solid particles are suspended in a liquid, and they can be seen and settle over time. An example of a suspension is muddy water.

9. What are colloids? Give examples.

Answer:
Colloids are mixtures where one substance is dispersed evenly throughout another, but the particles are larger than in a solution and do not settle over time. Examples include milk, fog, and gel. Colloids are homogeneous at the microscopic level but may appear heterogeneous.

10. Why is the separation of mixtures important in daily life?

Answer:
The separation of mixtures is important for various practical reasons, such as purifying drinking water, separating useful substances from waste, and extracting valuable components from natural resources. For example, oil and water can be separated to obtain pure oil for consumption.

11. Describe the method of separating a mixture of sand and salt.

Answer:
To separate a mixture of sand and salt:

Dissolve the salt: Add water to the mixture to dissolve the salt.
Filter the sand: Use a filter to separate the sand from the salt solution.
Evaporate the water: Heat the salt solution to evaporate the water, leaving behind the salt.

12. What is the importance of purity in substances like water and food?

Answer:
Purity is crucial in substances like water and food because impurities can affect health and the quality of consumption. Contaminants in water, for instance, can lead to diseases, and adulterants in food can affect nutrition and taste.

13. Explain how the process of chromatography is used to separate mixtures.

Answer:
Chromatography is a method used to separate different components of a mixture based on their movement through a stationary phase, usually a paper or a column. For example, it can be used to separate different pigments in a dye. As the solvent moves through the mixture, components with different solubility levels separate.

14. What are the differences between a solution, a colloid, and a suspension?

Answer:
The differences between the three are:

Solution: Homogeneous, particles are dissolved and cannot be seen.
Colloid: Particles are larger than in a solution but do not settle over time (e.g., milk).
Suspension: Heterogeneous, particles are large, can be seen, and settle over time (e.g., muddy water).

15. What is an example of a colloidal solution, and what are its characteristics?

Answer:
An example of a colloidal solution is milk. Its characteristics include:

Particles that do not settle over time.
Can scatter light (Tyndall effect).
Have particle sizes between 1 nm and 1000 nm.

16. What do you understand by the term ‘Tyndall effect’?

Answer:
The Tyndall effect refers to the scattering of light by the particles in a colloid or a suspension. This effect makes the path of light visible through the mixture. For example, when sunlight passes through fog, the beams of light can be seen due to the scattering by water droplets in the fog.

17. What is the role of solubility in forming a solution?

Answer:
Solubility is the property of a substance that determines how well it can dissolve in a solvent to form a solution. The higher the solubility of a substance in a solvent, the more of the solute can dissolve, forming a concentrated solution. For example, salt has high solubility in water.

18. How can we separate a mixture of iron filings and sulfur powder?

Answer:
A mixture of iron filings and sulfur powder can be separated using a magnet. Iron filings are magnetic and will be attracted to the magnet, while sulfur, being non-magnetic, will remain behind.

19. What is the difference between evaporation and boiling?

Answer:
Evaporation is the process by which liquid turns into vapor at the surface without reaching its boiling point. Boiling, however, occurs throughout the liquid when it reaches a specific temperature. Evaporation happens at all temperatures, while boiling happens at a fixed temperature (e.g., 100°C for water).

20. What is the significance of separating mixtures in industry?

Answer:
In industries, separating mixtures is essential for refining products, purifying materials, and ensuring the production of high-quality goods. For example, in the oil industry, crude oil is separated into different useful components (like gasoline, diesel, etc.) using fractional distillation.

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