Exam practice
Every question from the end of every unit, with hints and answers to open. After you check an answer, mark how you did, and come back to the ones you didn’t get.
22 questions
Unit 6 · Matter
Exercise (Matter)
2. Fill in the blanks
Matter exists in ______ states.
Answer
Matter exists in three states.
Heat changes the ______ of matter.
Answer
Heat changes the volume of matter. (It changes the state of matter too.)
Solid and ______ substances can’t be compressed.
Answer
Solid and liquid substances can’t be compressed.
The state of matter that has a fixed shape and a fixed volume is the ______.
Answer
The state of matter that has a fixed shape and a fixed volume is the solid.
Camphor changes to ______ when it is heated.
Answer
Camphor changes to gas when it is heated.
4. Answer these questions
What is matter?
Answer
Anything that has mass and takes up space is called matter. Examples: a stone, water, air, a table, plants and animals.
Write three differences between a solid and a liquid.
Answer
- A solid has a fixed shape. A liquid takes the shape of its container.
- A solid doesn’t flow. A liquid flows.
- In a solid, the particles are packed very close and held tightly in place. In a liquid, they are a little farther apart and slide over one another.
Why is air called a gas?
Answer
Because air behaves like a gas:
- it has no fixed shape or volume, and fills any container it is in;
- it can be compressed, as in a pumped-up tyre or ball;
- it flows and spreads out easily.
Why are heat and light not matter?
Answer
Heat and light have no mass, and they don’t take up space. Matter must have mass and take up space. So heat and light are not matter. They are forms of energy.
Can the state of matter be changed? How? Give examples.
Answer
Yes. The state of matter can be changed by heating or cooling it.
- Heating ice melts it into water. Heating water boils it into steam.
- Cooling steam turns it back into water. Cooling water in a freezer turns it into ice.
- Heated wax and ghee melt. When they cool, they turn solid again.
Water turns into steam when it boils. Show this in a diagram, so that the particles can be seen.
Answer
Draw a pan of boiling water. Draw two circles, as if looking through a magnifying glass. In the water, draw the particles close together and jumbled, touching. In the steam above, draw only a few particles, far apart, each with an arrow to show it flying fast.
Have you seen used plastic bags being collected? Why are they collected?
Answer
Yes. Used plastic bags are collected so they can be recycled. They are cleaned and heated until they melt. The melted plastic is made into new things, such as buckets, pipes and new bags. This keeps plastic out of rivers and fields. There it doesn’t rot away for hundreds of years, and it harms animals that eat it.
Exercise (Mixture)
2. Fill in the blanks
A substance mixed in a mixture is called a ______ of the mixture.
Answer
A substance mixed in a mixture is called a component of the mixture.
If the components of a mixture can be seen with the eyes, it is called a ______ mixture.
Answer
If the components of a mixture can be seen with the eyes, it is called a heterogeneous mixture.
Sand and water can be separated by ______.
Answer
Sand and water can be separated by filtration. (Sedimentation and decantation works too.)
A mixture of heavy and light solids, like rice and husk, is separated by ______.
Answer
A mixture of heavy and light solids, like rice and husk, is separated by winnowing.
Sugar water is an example of a ______ mixture.
Answer
Sugar water is an example of a homogeneous mixture.
4. Answer these questions
What is a mixture?
Answer
Two or more substances mixed together make a mixture. Each substance keeps its own properties. Examples: tea, soil, air and kheer.
Write the difference between a homogeneous mixture and a heterogeneous mixture.
Answer
- In a homogeneous mixture, the components are mixed evenly. They can’t be seen, and every part is the same. Example: salt water.
- In a heterogeneous mixture, the components are not mixed evenly. They can be seen with the eyes. Example: sand and water.
Why is air called a gas, and a mixture of gases?
Answer
- Air is called a gas because it has no fixed shape or volume, fills any container, can be compressed and spreads out easily.
- It is called a mixture of gases because it is made of many gases mixed together: mostly nitrogen and oxygen, with a little carbon dioxide, water vapor and other gases.
As soon as Biju opened a bottle of Coca-Cola, fizz came out. Why?
Answer
Coca-Cola is a mixture of a liquid and a gas. At the factory, carbon dioxide gas is squeezed into the drink, and the cap keeps it in. When Biju opened the bottle, the gas could escape. It came out of the drink as bubbles, all at once, so the drink fizzed.
Ramila mixed sand into the drinking water by mistake. She is afraid her mother will scold her. What would you tell her?
Answer
Don’t worry, Ramila! You can get the water back.
- Leave the water to stand for a while. The heavy sand will sink to the bottom (sedimentation).
- Then pour the clear water gently into a clean vessel, leaving the sand behind (decantation).
- To take out the last fine bits, pour the water through a clean, folded cloth or filter paper (filtration).
- Boil the water before drinking it, to be safe.