# NCERT Solutions for Class 9 Science Unit 2

## Is Matter Around Us Pure Class 9

### Unit 2 Is Matter Around Us Pure Exercise Solutions

Most of the substances in our surroundings are not in their pure form and are called mixture. Substances which are made of two or more matters and which can be separated by physical methods are known as mixtures, such as mixture of salt and water, mixture of sugar and water, mixture of different gases, air, etc.
In a mixture, components do not combine chemically or through any chemical change. In a mixture, components do not lose their properties.
Mixtures are of two types on the basis of their composition - Homogeneous mixture and Heterogeneous mixture.

### Question : Solutions of Questions on Page Number : 15

Q1 :

What is meant by a pure substance?

A pure substance is the one that consists of a single type of particles, i.e., all constituent particles of the substance have the same chemical nature. Pure substances can be classified as elements or compounds.

Q2 :

List the points of differences between homogeneous and heterogeneous mixtures.

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

Q3 :

Differentiate between homogeneous and heterogeneous mixtures with examples.

Q4 :

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

Q5 :

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.

Q6 :

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?

Q7 :

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 water breaking down into hydrogen and oxygen gas

• Dissolving common salt in water

• Making a fruit salad with raw fruits

• Burning of paper and wood

Q8 :

Name the technique to separate

(i) butter from curd

(ii) salt from sea-water

(iii) camphor from salt

Q9 :

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

Q10 :

What typeof mixtures is separated by the technique of crystallization?

### Exercise : Solutions of Questions on Page Number : 28

Q1 :

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.

Q2 :

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

Q3 :   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 Temperature in K 283 293 313 333 353 Potassium nitrate 21 32 62 106 167 Sodium chloride 36 36 36 37 37 Potassium chloride 35

Q4 :

Explain the following giving examples:

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

Q5 :

Classify each of the following as a homogeneous or heterogeneous mixture.

Soda water, wood, air, soil, vinegar, filtered tea

Q6 :

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

Q7 :

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) Brick

(h) Wood

(i) Air

Q8 :

Identify the solutions among the following mixtures:

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water

Q9 :

Which of the following will show the "Tyndall effect"?

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution

Q10 :

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

Q11 :

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