# NCERT Solutions for Class 9 Science Chapter 2 Is Matter around us Pure?

NCERT Solutions for Class 9 Science Chapter 2 Is Matter around us Pure? help students understand the concepts better and also enable them to memorize the topics faster. These solutions not only help students understand the concepts better but also enable them to score good marks in the exams.

Chapter 2 CBSE Class 9 Science NCERT Solutions can be used to check answers to questions, or to see how well they understand a concept. NCERT Solutions have been designed by experienced teachers keeping in mind the challenges that students face while trying to understand a concept.

## Chapter 2 Is Matter around us Pure? Class 9 Science NCERT Solutions

### In Text Questions

1. What is meant by a pure substance?

Solution

A material that consists of a single type of particles is known as pure substance. All constituent particles of pure substance have the same chemical nature.

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

Solution

3. Differentiate between homogeneous and heterogeneous mixtures with examples.

Solution

A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example: Salt in water, sugar in water, copper sulphate in water.
A heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example: Sodium chloride and iron fillings, salt and sulphur, oil and water.

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

Solution

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.

Solution

Mass of sodium chloride (solution) = 368
Mass of water (solvent) = 100 g
Total mass of solution = 100+36=136 g
Mass percentage of solution = Mass of solute/Mass of solution × 100
= 36/136 × 100
= 26.47%

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?

Solution

By distillation

2. Name the technique to separate:
(i) Butter from curd
(ii) Salt from sea water
(iii) Camphor from salt

Solution

(i) Centrifugation
(ii) Evaporation
(iii) Sublimation

3. What types of mixtures are separated by the technique of crystallisation?

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. For example, Salt from seawater.

1. Classify the following as chemical or physical changes:
(a) Cutting of trees
(b) Melting of butter in a pan
(c) Rusting of almirah
(d) Boiling of water to form steam
(e) Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
(f) Dissolving common salt in water
(g) Making a fruit salad with raw fruits
(h) Burning of paper and wood

Solution

(a) Physical change
(b) Physical change
(c) Chemical change
(d) Physical change
(e) Chemical change
(f) Physical change
(g) Physical change
(h) Chemical change

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

Solution

Pure substance : Water, salt and sugar, etc.
Mixture : Salt water, soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes and food.

### Exercise

1. Which separation techniques will 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.

Solution

(a) Crystallization or evaporation.
(b) Sublimation.
(c) Centrifugation or sedimentation.
(d) Chromatography.
(e) Centrifugation.
(f) Separating funnel.
(g) Hand-picking.
(h) Magnetic separation.
(i) Winnowing.
(j) Centrifugation.

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

Solution

(i) Heat the solvent, water, in a kettle. When the solvent boils, add the solute, milk. Milk and water forms a solution.
(ii) Then pour some tea leaves. Pour slowly hot solution of milk over tea leaves. Colour of tea leaves goes into solution as filtrate. The remaining tea leaves being insoluble remains as residue.

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)

(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:
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. For 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. For 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 : Sodium, silver, tin, silicon.
Compounds : Calcium carbonate, methane, carbon dioxide.
Mixtures : Soil, sugar solution, coal, air, soap, blood.

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.

Solution

(a) Growth of a plant
(b) rusting of iron
(d) cooking of food
(e) digestion of food
(g) burning of a candle