Question 1. Define matter.

Answer: Anything that has mass and occupies space is called matter. 

Question 2. What is volume ?

Answer: The amount of space occupied by a matter is called its volume. 

Question 3. What is mass ?

Answer: Mass is the quantity of matter contained in the body. 

Question 4. If an object weighs 6 kg on earth. What will be its weight on moon ?

Answer: Weight of body on moon = 1 / 6 th of its weight on earth ∴ Body will weigh 1 / 6 × 6 = 1 kg on moon 

Question 5. If an object is taken to the moon from the earth what will be its mass ?

Answer: Mass of a body does not change with change in gravity. So mass of a body will remain the same on moon. 

Question 6. Name the smallest particle from which matter is made up. Answer: The smallest particle from which matter is made up is atom. 

Question 7. What are molecules ?

Answer: Molecules are made of atoms. Molecules exhibit the properties of that kind of matter and has independent existance. 

Question 8. Give one difference between atoms and molecules. Answer: Atoms may or may not have independent existance. Molecules have independent existance. 

Question 9. Define :

(a) Intermodular force of attraction.

(b) Intermodular space.

Answer: (a) The molecules of matter are always in motion and attract each other with a force called intermodular force of attraction due to which they are held together.

(b) The molecules can move only when there are gaps or space between them, this space is called intermolecular space. 

Question 10. Classify the following into solids, liquids and gases. Oxygen, milk, common salt, wax, stone, water vapour, carbon-dioxide, sugar, mercury, coal, blood, butter, copper, coconut oil, kerosene.

Answer:

Solids : Common salt, Wax, Stone, Sugar, Coal, Butter, Copper. Liquids : Milk, Mercury, Blood, Coconut, oil, Kerosene.

Gases : Oxygen, Water, vapour, Carbondioxide. 

Question 11. Why do solids, liquids and gases differ in their physical states? Answer: 

1. • Inter molecular force of attraction.
   • Inter molecular spaces are two important properties of matter that account for the different states of matter. 

Question 12. What are fluids? Give two examples.

Answer: Substances that can flow are called fluids. e.g. gases (oxygen, hydrogen), liquids (water, petrol, sulphuric acid). 

Question 13. Define inter conversion of states of matter.

Answer: The process by which matter changes from one state to another and back to original state, without any change in its chemical composition. 

Question 14. What are the two conditions for the inter conversion of states of matter?

Answer: Two conditions are : change in 

1. • Temperature
   • Pressure 

Question 15. How a liquid changes into its gaseous state ? Explain ?

Answer: As a liquid is heated, its particles starts gaining energy and move more vigorously which increases the gaps between the particles and decreasing the force of attraction. Ultimately a liquid changes into gaseous state. 

Question 16. Water cycle is an example of inter conversion of states of water. Explain.

Answer: Water from oceans, rivers lakes from leaves of trees (transpiration) changes into vapours when temperature increases or evaporates and enters the atomsphere as clouds when temperature falls the vapors change into water and some of it in the form of snow fall on mountains and earth in the form of water and hales and this continues. Thus water cycle is example of inter convertion of states of water. 

Question 17. State the general properties of a solid.

Answer: General Properties Of A Solid : 

1. • Solids are hard that is, they have a definite shape and volume.
   • Solids are generally in compressible.
   • Solids are rigid, that is, they do not flow. 

Question 18. What is the relation between intermolecular space and intermolecular force?

Answer: The force of attraction between the molecules of a given substance is called intermolecular force and the space between these molecules is called intermolecular space. The basic relation between the two is that they are inversely proportional to each other. More is the intermolecular force lesser is the intermolecular space and vice-versa. 

Question 19. Why liquids do not have a definite shape? Answer: Molecules of a liquid are held by weak intermolecular förces. This force is sirong enough to hold the molecules together but not strong enough to hold them at fixed positions. As a result liquids have a fixed volume but not shape. 

Question 20. What happens when a solid is heated ? Answer: When a solid is heated, its molecules gain energy and vibrate faster. A stage comes ,when they overcome intermolecular force of attraction and start moving from each other. This results in melting of solid. 

Question 21. Give reasons for the following. 

1. Gases can be compressed easily. 

Ans. The reason for this property of gases is that there is very large intermolecular space between gas molecules. On mere applying pressure, they are easily compressed.

2. Liquids can flow easily. 

Ans. In liquids intermolecular force is weaker than that of solids. So molecules in a liquids can slip over one another and liquids can flow unlike solids.

3. We need to classify things. 

Ans. We need to classify things in order to distinguish them. In this way, things can be categorized and can be easily studied.

4. Pure substances have fixed melting or boiling points. 

Ans. Pure substances consists of only one kind of matter. All the particles of a pure substance are alike. It has a definite composition and similar properties. This is the reason that pure substances have fixed melting or boiling points.

5. Electricity is not considered matter. 

Ans. Electricity neither has mass nor it occupies space. Beside it can not be seen by our eyes. This is why electricity is not considered matter 

Question 22. Define the following term. 

Answer: 

1. • Matter — Anything that has mass and occupies space is called matter.
   • Intermolecular force — The force of attraction between the molecules of a given substance is called inter molecular force.
   • Element — It is defined as that pure substance which contains only one type of atoms e.g. hydrogen, chlorine.
   • Atom — An atom is the smallest part of an element that takes place in a chemical reaction.
   • Molecule — A molecule is a smallest part of a compound that exists independently. 

Question 23. Write your observation and conclusion for the following:

(1) When a small stone is gently dipped into a glass filled with water.

(2) When one of the balloons suspended to the metre scale is punctured while other remains inflated ?

Answer: (1) You will see that some water flows out of the tumbler and collects in the bowl. Remove the stone from the tumble. The level of water in the tumbler comes down. Now, pour the water collected in the bowl back into the tumbler. The glass tumbler is filled again. This is because the stone occupied space and therefore drives the water out of the tumbler. This proves that not only solids but liquids also occupy space.

(2) Take two similar balloons and inflate them equally. Suspend one balloon to the left of a metre scale and the other one to the right of it, as shown in the figure below. Balance the scale in the middle with the help of a peg. 

Question 24. Give reasons :

(a) Why do liquids and gases flow but solids do not ?

(b) A gas fills up the space available to it.

(c) The odour of scent spreads in a room.

(d) We can walk through air.

(e) Liquids have definite volume but no difinite shape.

Answer: (a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps in solid molecules is less and molecular force of attraction very strong.

(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them.

(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room. OR Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room.

(d) The molecules of air are far apart i. e. large gaps and we can walk through air easily.

(e) The molecules of liquid are loosely packed and inter molecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape. 

Question 25. Give reasons :

(a) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass does not rise.

(b) When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.

(c) A red ink drop added to small amount of water in a glass turns water red in some time.

Answer: (a) Add one teaspoon of sugar to it and stir. The sugar disappear but the level of water in the glass does not rise that means the volume of water has not increased. Because the sugar particles are adjusted between the water molecules. The shows that there are intermolecular gaps in water. 

(b) This shows that gases can fill up all the space that they get, and they have neither a fixed shape nor a fixed volume. They have no free surfaces, either. (c) If we put a drop of red ink in a glass of water, its particles diffuse with particles of water slowly but continuously and the water turns red.