You Must Know
1. Grouping of materials, having similar properties, is known as classification.
2. Classification is done to make the study of materials and their properties easier.
3. Materials can be classified as naturally occurring and synthetic (man-made) materials.
4. All materials are made up of matter, that is, they have mass and occupy space.
5. Matter exists in three physical states, namely, solid, liquid and gas.
6. These states of matter differ from each other in properties due to differences in the nature of packing of particles in them.
7. Matter can be classified on the basis of different properties like appearance and feel, transparency, tendency to float or sink, diffusion, dissolution and so on.
8. Some materials allow light to pass through them, that is, they are transparent.
9. Some materials do not allow light to pass through them, that is, they are opaque.
10. Materials, which are lighter than water, generally, float over it; those, which are heavier than water, generally, sink in it.
11. Gases diffuse into each other quite readily; liquids diffuse much more slowly and solids generally do not diffuse into each other.
12. Some substances dissolve in water while some others do not dissolve in it.
13. The maximum amount of a substance, that can be dissolved in a given volume of water is called the solubility of that substance in water.
14. The solubility of a solid, in water, generally, increases on increasing the temperature.
15. Solubility of a gas, in water, decreases on increasing the temperature.
16. A solution which cannot dissolve more amount of a given substance at a given temperature is called a saturated solution.
Something To Know
A. Fill in the blanks.
1. The process of grouping objects with similar properties is called classification.
2. Anything that occupies space and has mass is called matter.
3. In the gaseous state of matter, the constituent particles have very little hold on one another.
4. Light does not pass through a blackboard as it is an opaque object.
5. Smell of a perfume reaches us by the process of diffusion.
B. Write True or False for the following statements.
1. Air is a man-made material. False
2. A thin polythene sheet is transparent. True
3. Pebbles float on water. False
4. . Diffusion is the mixing of the particles of two materials, on their own. True
5. Oxygen gas is slightly soluble in water. True
C. Tick (✔) the correct option.
1. The state/states of matter, that have both a fixed shape and a definite volume, is/are-
liquids and solids
solids only (✔)
gas and liquids
liquids only
Answer – solids only(✔)
2. Your book is made up of matter, because it-
has mass.
occupies space and has some mass. (✔)
occupies space.
does not float on water.
Answer – occupies space and has some mass. (✔)
3. Which of the following is an opaque material?
a piece of wood (✔)
pure air
a plane, thin sheet of glass.
water in a clear glass container
Answer – a piece of wood(✔)
4. In which of the following cases would diffusion be the fastest?
gas in another gas. (✔)
a solid in a liquid.
liquid in another liquid.
a gas in a liquid.
Answer – gas in another gas. (✔)
5. Which of the following is insoluble in water?
mustard oil (✔)
carbon dioxide
sugar
common salt
Answer – mustard oil(✔)
D. Answer the following questions in brief.
1. Define the following:
(a) Natural materials
Answer – The materials which occur naturally are called natural materials. Examples are water, air, and milk.
(b) Transparent materials
Answer – Materials that allow light to pass through it are called transparent materials. Examples are glass, air, and pure water.
2. Name any three materials that are (i) transparent (ii) opaque in nature.
Answer – (i)Transparent materials – glass, air, pure water.
(ii)Opaque material – wall, blackboard, thick plastic sheet.
3. Which state of matter (i) can (ii) cannot easily change its shape and volume? Why?
Answer – (I) Gases can easily change their shape and volume because their particles are very far from each other and can move easily.
(ii) Solid cannot easily change its shape and volume because the particles are very tightly packed with each other and cannot move.
4. Why do materials diffuse into each other?
Answer – Materials diffuse into each other because the particles in the materials are free to move as in gases and liquids.
5. Define the term ‘solubility’. How does it change on increasing the temperature of water?
Answer – Solubility is the maximum amount of a substance that can be dissolved in a given volume of a given liquid. On increasing the temperature of the water, the solubility of water also increases.
6. Name three materials that are (i) soluble (ii) insoluble in water.
Answer – (I)Salt, sugar, lemon juice are soluble in water
(ii) Sand, pebbles, chalk pieces are insoluble in water.
E. Answer the following questions.
1. Why do solids have a fixed shape and a definite volume?
Answer – Solids have a fixed shape and a definite volume because the particles in a solid are tightly packed with each other and cannot move.
2. Briefly describe an activity to show that pure water is a transparent liquid.
Answer – A glass tumbler is taken and it is filled with water. It is held against the light and we can look through it easily. This proves that pure water is transparent.
3. Describe an activity to show that a solid can diffuse slowly into a liquid.
Answer – Some clean water is taken in a glass jar and some crystals of potassium permanganate are dropped in water. We can see that the pink colour spreads slowly in the water. This shows that the diffusion of a solid in a liquid is slow.
4. What is a ‘saturated solution? How can one prepare a saturated solution of common salt in water?
Answer – The solution, in which more of the given substance cannot be dissolved at a given temperature is called a saturated solution.
Activity: Glass tumbler, half-filled with water is taken. Half a teaspoon of salt is added to it and stirred well. We have to keep on adding salt in half teaspoon amounts till we notice that salt is no more dissolving in the given volume of water. This means the maximum amount of sugar has been dissolved in a given volume of water. In this way, we can get a saturated solution of salt in water.
5. Suggest one activity to show the effect of temperature on the solubility of a solid in water.
Answer – Activity: Equal volume of water is taken into separate glass tumblers. The water in one of the tumblers is heated. Now equal amounts of sugar are added into tumblers and stirred. We have to keep on adding sugar till we get a saturated solution. We will find out that more sugar is dissolved in hot water which shows an increase in temperature increases the solubility of a substance in water.
Value Based Question
Neha went to a village to attend the marriage of her cousin. She was very much upset when she observed that there was no cleanliness in, and around, many houses. She used a gentle, polite and slow approach to make the villagers realise the importance, and necessity, of keeping their surroundings neat and clean. She was happy to find the village very much cleaner by the time she left. While leaving, she told her cousin that her success was similar to that of blue ink drops which slowly make the water in a bowl uniformly light blue when they are dropped in it.
1. State the values displayed by Neha.
Answer – Values displayed by Neha are cleanliness, responsible.
2. Name the process through which blue ink drops make the water uniformly blue.
Answer – The process through which blue ink drops make the water uniformly blue is called diffusion.
3. Let each student think of an incident, or a situation, in which the efforts of one person brought a useful, or desirable, change in that situation.
Answer – A social worker worked hard to arrange dustbins in several areas of our town which helped in keeping cleanliness in our town.
Something To Do
1. Visit a nearby departmental store and observe how classification of the materials is useful. Try to find out the basis of classification of different materials. Write your observation in a tabular form.
Answer – Do it yourself.
2.Make a model to show the arrangements of particles in the three states of matter.
Answer – For this small bead can be used where beads represents a particles.
3. Fill the boxes with suitable words on the basis of the clues given below.
Answer –
Down↓
a.It has a definite volume and a fixed shape. SOLID
c.The solution that has the maximum amount of a substance, dissolved, in a given volume of it. SATURATED
Across →
b. It has mass and occupies space. MATTER
d. It has a definite volume but no fixed shape. LIQUID
e. Particles of two materials mixing on their own. DIFUSSION