NCERT Solutions for Chapter 2 Is Matter Around Us Pure Class 9 Science

NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Chapter Name	NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure
Topics Covered	NCERT Intext Questions NCERT Exercise Solutions
Related Study	NCERT Solutions for Class 9 Science NCERT Revision Notes for Class 9 Science Important Questions for Class 9 Science MCQ for Class 9 Science NCERT Exemplar Questions For Class 9 Science

NCERT Intext Questions

1. What is a pure substance?

Solution

A pure substance is one, which contains only one type of atoms or molecules in a specific arrangement in any part of the sample taken. Example : Water, diamond.

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

Solution

Homogeneous Mixture	Heterogeneous Mixture
Mixture which has a uniform composition throughout. Example: Sugar in water.	Mixture which contain physically distinct parts and have non–uniform composition. Example: Mixture of salt and sulphur.

3. Differentiate between homogeneous and heterogeneous mixtures with examples.

Solution

Homogeneous Mixture	Heterogeneous Mixture
Components are uniformly distribited throughout the mixture.	Components are not completely mixed and can be identified.
No visible boundaries of separation.	Visible boundaries of separation.
Same composition.	Different compostion,
Examples : Rainwater, vinegar, etc.	Examples : Seawater, pizza etc.

4. Differentiate between homogeneous and heterogeneous mixtures with examples.

Solution

Property	Solution	Suspension	Sol
Nature	Homogeneous	Heterogeneous	Heterogeneous
Particle size	Less than 1 nm	More than 100 nm	10-7 – 10-5 cm
Stability	Very stable	Unstable	Quite stable
Tyndall effect	No	Yes/No	Yes
Appearance	Clear	Opaque	Generally
Visibility	Not Visible	Visible with naked eye	Visible by microscope
Diffusion	Fast diffusion	Do not diffuse	Slow diffusion
Settling	Do not settle	Settle on their own	Settled in centrifugation
Example	Salt and sugar in water	Sand in water, dusty air	Milk, blood, smoke

5. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 Kelvin. Find its concentration at this temperature.

Solution

Mass of solute (NaCl) = 36 g
Mass of solvent (H₂O) = 100 g
Mass of solution (NaCl + H₂O) = 136 g
Concentration = (Mass of solute)/(Mass of solution) × 100
Concentration = (36/136)× 100 = 26.47%
Hence, the concentration of the solution is 26.47% .

6. 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?

Solution

The mixture of miscible liquids whose boiling point difference is more than 25°C such as kerosene and petrol can be separated by a technique called simple distillation. The principle of separation is based on the volatility of the substances.

The process of distillation is as follows :

1. Take the mixture in a distillation flask.
2. Fit it with a thermometer and heat the mixture.
3. Petrol has a lower boiling point and evaporates first.
4. As the vapour rises up and reach the condenser, the temperature is decreased and the vapour is condensed into liquid and is collected in a flask.
5. The kerosene that has relatively higher boiling point remains in the flask in the liquid form.
6. Hence, the liquids are separated.

7. Name the techniques used to separate the following :
(a) Butter from curd
(b) Salt from seawater
(c) Camphor from salt

Solution

(a) The butter is separated from the curd by the process of centrifugation.
(b) Simple evaporation is used to separate salt from seawater.
(c) Camphor does not undergo liquid phase during the phase change. Therefore, sublimation process is used for the separation of camphor from the other substance.

8. What type of mixtures can be separated by crystallization?

Solution

Crystallization is a technique of separation of solid from a liquid solution . It can be used to purify solid with some impurities in it. Example : Salt from scawater.

9. Classify the following as physical or chemical change : 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 water breaking down into hydrogen and oxygen gases, Dissolving common salt in water, making fruit salad with raw fruits, burning of paper and wood.

Solution

	Physical change		Chemical change
1.	Cutting the trees	1.	Rusting of almirah
2.	Melting of butter in a pan	2.	Passing of electric current through water and water breaking into hydrogen and oxygen gases.
3.	Boiling of water to form steam	3.	Burning of paper and wood
4.	Dissolving common salt in water
5.	Making fruit salad with raw fruits

10. Separate these are pure substances and mixtures.

Solution

• Pure substances : water, salt,. iron, diamond
• Mixture : sand, salad, concrete, air, steel

NCERT Exercises Solutions

1. Identify the separation method, you use 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

Solution

	Substances	Separation Method
(a)	Sodium Chloride from its solution in water	Evaporation
(b)	Ammonium chloride from a mixture containing sodium chloride and ammonium chloride	Sublimation
(c)	Small pieces of metal in the engine oil of a car	Filtration
(d)	Different pigments from an extract of flower petals	Chromatography
(e)	Butter from curd	Centrifugation
(f)	Oil from water	Separating funnel
(g)	Tea leaves from tea	Filtration
(h)	Iron pins from sand	Magnetic separation
(i)	Wheat grains from husk	Winnowing/sedimentation
(j)	Fine mud particles suspended in water	Decantation and filtration

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

Solution

1. We take a cup of milk in a vessel that acts as a solvent and heat it.
2. We drop in the tea leaves or the powdered tea leaves into the milk as solute and continue heating.
3. The tea leaves or the powdered tea leaves used is insoluble in the milk and is visible even after the heating.
4. Now, to the boiling solution, add sugar and stir it.
5. The sugar acts yet another solute, but in this case, it is soluble in the solvent.Due to continued stirring, the sugar completely becomes soluble in the tea solution and a saturation level is reached.
6. After enough heating, filter the solution using a medium. When done, the insoluble tea leaves stays behind as residue and the soluble essence and sugar passes through the filter medium and is collected as the filtrate.

3. Pragya tested the solubility of three different substances at different temperatures and collected the data, which is given in the following table. (As grams of substance dissolved in 100 grams of water to form a saturated solution)

Substance Dissolved	Temperature is Kelvin and solubility
	283	293	313	333	353
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?
(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 down? 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?

Solution

(a) Mass of KNO₃ required to produce a saturated solution of KNO₃ in 100 g of water at 313 K = 62g. Mass of potassium nitrate required to produce a saturated solution in 50 g of water = 62 × 50 ÷ 100 = 31
Hence, 31 g of potassium nitrate is required.
(b) Crystals of potassium chloride will be obtained on cooling the solution.
(c) Solubility of each salt at 293 K is as follows :
Potassium nitrate = 32 g
Sodium chloride = 36 g
Potassium chloride = 35 g
Ammonium chloride = 37 g
Thus, ammonium chloride salt has the highest amount of solubility when compared to any other
salt at 293 K.
(d) Solubility of salts increases with temperature.

4. Define the terms :
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension

Solution

(a) Saturated solution: A saturated solution is a solution in which the maximum amount of solute has been dissolved at a particular temperature.
(b) Pure substance: Pure substance consist only one type of atoms or molecules or compounds.
(c) Colloid: A colloid is heterogeneous mixture in which one substance is scattered as very fine particles in a continuous medium of another substance. These particles cannot be seen by naked eye. Example : Ink, Blood.
(d) Suspension: A suspension is a heterogeneous mixture containing solid particles that are big enough to settle down. Particles of suspension are visible to the naked eye. Example : Chalk powder, Paints, etc.

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

Solution

• Homogeneous: soda water, vinegar, filtered tea.
• Heterogeneous: wood, air, soil.

6. How would you prove that any colourless liquid, given to you is pure water?

Solution

If the colourless liquid boils at 100°C, then it is pure water. This is because any pure substance has fixed boiling and melting point.

7. Which of the following materials fall into the category of pure substances?
(a) Ice,
(b) milk,
(c) iron,
(d) hydrochloric acid,
(e) calcium oxide,
(f) mercury,
(g) brick,
(h) wood,
(i) air

Solution

Ice, iron, hydrochloric acid, calcium oxide and mercury are the pure substances.

8. Identify the solutions among the following mixtures :
(a) Soil,
(b) Seawater,
(c) Air,
(d) Coal,
(e) Soda water

Solution

Seawater, air and soda water are the solution.

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

Solution

Milk and the starch solution shows Tyndall effect.

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

Solution

Elements	Compounds	Mixtures
Sodium	Calcium carbonate	Soil
Silver	Soap	Sugar solution
Tin	Methane	Coal
Silicon	Carbon dioxide	Air, Blood

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

Solution

The following changes are chemical changes :
(a) Growth of a plant
(b) Rusting of iron
(d) Cooking of food
(e) Digestion of food
(g) Burning of candle