�

Chemistryfor students of class IX

Score n learn

CONTENTS

Matter 7Chapter 1

Matter - Pure and Impure 35Chapter 2

Atoms and molecules 63Chapter 3

Structure of the atom 87Chapter 4

The following 3 pages will give you a

glimpse of how effectively we have used

illustrations along with simple language

to explain a concept. The following pages

are from the part of the chemistry book

for IX grade, these pages detail -

“Types of mixtures”

37

Types of mixtures:Based on the nature of the constituents that are mixed with each other, mixtures can be categorised into two types: a) Homogeneous mixtureb) Heterogeneous mixture

a) Homogeneous Mixture: A mixture is said to be homogeneous if its constituents are uniformly distributed and are not physically distinct. For example, sugar solution, salt in water, etc.

Properties of a homogenous mixture:

1. Constituents are uniformly distributed.2. Constituents are not physically distinct from each other. Hence,

homogeneous mixtures exhibit a unique property.3. To separate the individual components, one needs to use physical

processes such as evaporation, boiling, etc.

b) Heterogeneous Mixture: A mixture is said to be heterogeneous if its constituents are not uniformly distributed and are physically distinct. For example, in a mixture of sand and soil in water, the constituents are physically distinct and are not uniformly distributed.

Properties of a heterogeneous mixture:

1. Constituents are not uniformly distributed.2. Constituents are physically distinct from each other. Hence, the

constituents exhibit their own properties.3. Individual components can be separated by physical or manual

processes.

What are the differences between homogeneous and heterogeneous mixtures?

Homogeneous mixture Heterogeneous mixture

1. Constituents are uniformly distributed.

2. Constituents are not physically distinct from each other.

3. Constituents can be separated by physical processes. They cannot be separated manually.

1. Constituents are not uniformly distributed.

2. Constituents are physically distinct from each other.

3. Constituents can be separated by physical and manual processes.

Know more

An alloy is a mixture of two or more metals or a metal and a non metal. For example, brass is a mixture of 30% zinc and 70% copper.

38

Take four containers and label them A, B, C, and D. Fill containers A and B with 50 mL of water. Add one spatula of copper sulphate in container A and two spatulas of copper sulphate in container B. Mix two spatulas of copper sulphate and one spatula of potassium permanganate in container C. Mix two spatulas of copper sulphate and two spatulas of potassium permanganate in container D.

Figure 1: Preparing homogenous and heterogeneous mixtures

Result of the activity: 1. The colour of the mixtures present in containers A and B will be blue.

The intensity of the colour will be uniform throughout the solution. However, the colour of the solution in container B will be slightly more intense than that in container B.

2. The mixtures present in containers C and D will have physically distinct parts. The compositions of these mixtures will be non-uniform.

Conclusion:Containers A and B contain homogeneous mixtures of copper sulphate and water. The physical properties (colour, concentration, etc.) of the mixtures are uniform throughout. Containers C and D contain heterogeneous mixtures of potassium permanganate and copper sulphate. In these containers, the crystals of potassium permanganate and copper sulphate are physically distinct.

Take three beakers and label them A, B, and C. Fill each beaker with 50 mL of water. Add a few crystals of copper sulphate in beaker A. Add one spatula of chalk powder in beaker B. Add a few drops of milk in beaker C. Stir the contents of all the beakers using a glass rod and use a torch to direct a beam of light through each beaker. After this, leave the mixtures undisturbed for 5-10 minutes.

Will the particles in the all the three mixtures be visible?No. Only the particles in beaker B will be visible.

In the Laboratory

1

In the Laboratory

2

You can perform the same experiment at home using sugar and salt replacing copper sulphate and potassium permanganate.

Know more

39

Will the path of the light coming from the torch be visible in all the beakers? No. The path of the light coming from the torch will not be visible in beaker A.

In which beaker will the particles settle after 5-10 minutes? The particles in beaker B will settle after 5-10 minutes and they can be filtered using a filter paper.

Figure 2: Different types of mixtures

Observation:1. The particles in beakers A and C are not visible.2. The rays of light coming from the torch are not scattered in beaker A

and thus, the path of light is not visible. However, the path of the light coming from the torch is visible in beakers B and C.

3. The particles in beaker B settle after 5-10 minutes.

Result of the activity: It can be concluded from these observations that beaker A has a homogenous mixture, while beakers B and C have heterogeneous mixtures.

Explanation:A solution is a homogenous mixture. Particles in a solution are very small in size and hence, light is not scattered by them. This is the reason why particles are not visible in beaker A and the path of the light from the torch is also not visible.In beaker B, the particles are clearly visible. It is a heterogeneous mixture. Such a mixture is called a suspension.The mixture in beaker C seems to be a homogeneous mixture. However, it is a heterogeneous mixture and hence, it is able to scatter light. This means that individual particles do exist in the mixture, but they are not visible to the naked eye. Such a mixture is called a colloidal solution.It can be concluded on the basis of the activity that:

Air contains suspended water droplets and dust particles which makes it a heterogeneous mixture.

Mixture1) Homogeneous - A) Solution

2) Heterogeneous - B) SuspensionC) Colloidal solution

This book contains expected learning objectives from a

chapter, simple content supported with lot of illustrations and

sectional assessments and comprehensive exercises at

the end of every chapter. To get this book delivered at

your address, kindly participate in the offer which is detailed at

http://www.meritnation.com/newsletter/meritnation_20090717

Access Restricted