# NCERT Solutions for Class 9 Science Chapter 2

NCERT Solutions for Class 9 Science Chapter 2 – Is matter around us pure, contains solutions to various questions in Exercises for Chapter 2. Is matter around us pure Class 9 NCERT Solutions have been explained in a simple and easy to understand manner. We are providing all subjects which can be accessed by clicking here.

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### NCERT Solutions for Class 9 Science Chapter 2 – Is matter around us pure – NCERT Exercises

NCERT Solutions for Class 9 Science Chapter 2 – Is matter around us pure, Exercises includes all in text and exercise solved questions which helps you to understand the topic covered in Chapter 2 Is matter around us pure, in a better manner to help you to score good marks in your examinations.

INTEXT QUESTIONS:

Page 15

1. What is meant by a substance?

A pure substance means that it consists of only one type of particles. All the constituent particles have the same characteristic properties and they cannot be separated by physical processes.

2. List the points of difference between homogeneous and heterogeneous mixtures.

### Page 18

1. Differentiate between homogeneous and heterogeneous mixtures with examples.

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

3.To make a saturated solution, 36g of sodium chloride is dissolved in 100g of water at 293K. Find it’s concentration at this temperature.

Mass of solute (Sodium Chloride) = 36g

Mass of solvent (Water) = 100g

Mass of solution = Mass of solute + Mass of solvent = 36g + 100g = 136g

Concentration = (Mass of solute/ Mass of solution) x 100

= (36/136) x 100 = 26.47%

### Page 24

1.How will you separate mixture containing kerosene and petrol (Difference in their boiling points is more than 25°C), which are miscible with each other.

A mixture of two miscible liquids such as kerosene and petrol whose boiling points differ by more than 25°C, can be separated by the technique of simple distillation.

Method of separation –

• Take the mixture of kerosene and petrol in a distillation flask.
• Thermometer has to be fitted in the flask.
• Then, heat the mixture slowly.
• Petrol with lower boiling point will distill out first, leaving the kerosene with higher boiling point behind.

2.Name the technique used to separate

i. Butter from curd

ii. Salt from sea water

iii. Camphor

i. Centrifugation

ii. Evaporation

iii. Sublimation

3.What type of mixture is separated by the technique of crystallization?

Crystallization technique is used to purify solids from liquids which have some impurities and have sufficiently different solubility from the impurities present. For example, impure copper sulphate, alum, nitrate, sea-salt, etc can be separated by crystallization.

1.Classify the following as physical or chemical changes.

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

Physical Changes-

Cutting of trees, melting of butter in a pan, boiling of water to form steam, dissolving common salt to water, making a fruit salad with raw fruits

Chemical Changes-

Rusting of almirah, passing of electric current through water and the water breaking down, burning of water and wood

2.Try segregating the things around you as pure substances or mixtures

Pure Substances-

Distilled water, diamond, graphite, raw rubber

Mixtures-

Curd, ice-cream, kerosene oil, cooking oil, steel, vulcanized rubber, solder wire

NCERT Exercise – Page 28

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.

(a) Evaporation or distillation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Separating funnel
(g) Filtration
(h) Filtration using a magnet
(i) Blowing air or seiving
(j) Using alum/filter paper

2.Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

• Take some water in a container and heat it on a burner.
• Then add some tea leaves. Water acts as a solvent and tea-leaves as a solute. It is insoluble in water.
• Add some sugar and heat till it dissolves completely. Sugar is completely soluble in water.
• Add milk which is soluble in water. Boil the contents.
• Filter the mixture through a sieve
• Tea collected in the cup as filtrate and tea leaves collected on the strainer as residue.

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).

(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?
(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 us the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?

(a) Mass of potassium nitrate present in 100g of water in a saturated solution at 313K = 62g

Thus, Mass of potassium nitrate present in 50g of water in a saturated solution at 313K = [(62/100) x 50]g = 31g

(b) When a saturated solution of potassium chloride at 353K is cooled, the solubility of potassium chloride in water decreases. As a result, the amount of potassium chloride which exceeds its solubility at lower temperature separates out as crystals.

(c) Solubility of potassium nitrate at 293K = 32g

Solubility of sodium chloride at 293K = 36g

Solubility of potassium chloride at 293K= 35g

Solubility of ammonium chloride at 293K = 37g

From the above data, it is clear that the ammonium chloride has the highest solubility at 293K

(d) The solubility of a salt generally increases with temperature. The increase Is however different for different salts.

4.Explain the following giving examples.

(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension

(a) Saturated solution –

A solution which contains the maximum amount of solute dissolved in a given amount of solvent at a particular temperature is called as saturated. Example- In aqueous  solution of sugar, no more sugar can be dissolved at room temperature after a certain point.

(b) Pure Substance –

A pure substance consists of particles of only one kind of matter. Pure substance can be either elements (ex. Copper, iron etc) or compounds (ex. Sugar, common salt, etc).

(c) Colloid-

Colloids are heterogeneous mixtures in which particle size lies in between that of true solutions and suspension, they are too small to be seen by naked eyes. However, these particles can scatter a beam of light. Example- Milk, smoke , etc

(d) Suspension-

Suspensions are heterogeneous mixtures in which solids are dispersed in liquids. Solute particles do not dissolve but remain suspended throughout the medium. The particles are big enough to be seen by naked eyes. Example- Paints, etc

5. Classify each of the following as a homogeneous or heterogeneous mixture : soda water, wood, air. soil, vinegar, filtered tea.

(a) Homogenous Mixture: Soda water, vinegar, air, and filtered tea

(b) Heterogeneous Mixture : Wood, soil

6. How would you confirm that a colourless liquid given to you is pure water?

If the boiling point and freezing point of the given liquid comes out to be 100°C and 0°C respectively at atmospheric pressure, it confirms that the given liquid is pure water.

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.

Ice, Iron, Hydrochloric acid, Calcium oxide and mercury are pure substances since they consist of particles of only of kind of matter.

8. Identify the solutions among the following mixtures.

(a) Soil
(b) Sea water

(c) Air
(d) Coal

(e) Soda water.

(b) Sea water and (e) soda water are solutions.

9. Which of the following show “Tyndall effect”?

(a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution.

(b)Milk and (d)starch solution

10. Classify the following into elements, mixtures and compounds

(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

Elements – Sodium, Silver, tin, Silicon

Compounds- Calcium carbonate, carbon dioxide, and methane

Mixtures- Soil, Sugar solution, coal, air, soap, and blood

11. Which of the following are chemical changes.

(a) Growth of plant, (b) rusting of iron, (c) Mixture of iron filings and sand, (d) Cooking of food, (e) digestion of food, (f) Freezing of water, (g)Burning of candle

Chemical changes are:

(b)Rusting of iron, (d)Cooking of food, (e)Digestion of food, and (g) Burning of candle.

### Topics Covered in Is matter around us pure Class 9 Science

1. Elements, compounds and mixtures
2. What is a Solution
• Concentration of a Solution
• What is a suspension?
• What is a Colloidal Solution
3. Separating the Components of a Mixture
4. Physical and Chemical Changes
5. What are the Types of Pure Substances?