Physical and Chemical Changes Class 7 Extra Questions and Answers Science Chapter 6

Physical and Chemical Changes Class 7 Extra Questions and Answers Science Chapter 6 PDF are solved by experts and will guide students in the right direction. Students can get how to tackle different questions easily by solving the Extra Questions for Class 7 Science Question bank on a regular basis.

Class 7 Science Chapter 6 Extra Questions and Answers Physical and Chemical Changes

Extra Questions for Class 7 Science Chapter 6 Physical and Chemical Changes with Answers

Physical and Chemical Changes Class 7 Extra Questions Very Short Answer Type

Question 1.
Why is cutting of paper a physical change?
Answer:
Because properties of paper do not change on cutting.

Question 2.
A piece of chalk becomes powdery on pressing. Which type of change is it?
Answer:
Physical.

Question 3.
What is freezing mixture?
Answer:
A mixture of ice and common salt.

Question 4.
What happens when water is heated?
Answer:
It gets converted into vapours.

Question 5.
What are physical properties?
Answer:
Properties such as shape, size, colour and state of a substance are called its physical properties.

Question 6.
In which type of change, no new substance is formed?
Answer:
Physical change.

Question 7.
Write equation for burning of magnesium ribbon.
Answer:
Magnesium (Mg) + Oxygen (O₂) → Magnesium Oxide (MgO)

Question 8.
Which type of change is explosion of a firework?
Answer:
Chemical change.

Question 9.
What happens if a cut apple is kept open for a while?
Answer:
The open surface acquires a brown colour.

Question 10.
Write the necessary conditions for rusting.
Answer:
Presence of water vapour and air.

Physical and Chemical Changes Class 7 Extra Questions Short Answer Type 1

Question 1.
Is melting of ice a chemical change? Give reason.
Answer:
No. When ice melts into water, no new substance is formed. Only the physical form of ice is changed. So, it is not a chemical change.

Question 2.
What happens when a hack-saw blade is heated?
Answer:
When a hack-saw blade is heated, it becomes red in colour. It starts emitting light.

Question 3.
What happens when magnesium oxide is dissolved in water? Write the chemical equation for the reaction.
Answer:
On dissolving magnesium oxide in water, magnesium hydroxide is produced. This chemical change can be written in the form of the following equation:

Magnesium oxide (MgO) + Water (H₂) → Magnesium hydroxide [Mg(OH)₂]

Question 4.
Write two importances of chemical changes.
Answer:

Extraction of all metals requires chemical changes.
Useful new materials, such as plastics and detergents, are produced by chemical reactions.

Question 5.
Why is it advised not to play with fireworks?
Answer:
Explosion of a firework is a chemical change. Such an explosion produces heat, light, sound and harmful gases that pollute the atmosphere. That is why, it is advised not to play with fireworks.

Question 6.
What is stainless steel?
Answer:
Stainless steel is an alloy of iron which does not rust, hence the name stainless steel. It is made by mixing iron with carbon and metals like chromium, nickel and manganese.

Physical and Chemical Changes Class 7 Extra Questions Short Answer Type 2

Question 1.
What happens when iron nail is dipped into copper sulphate solution?
Answer:
The blue colour solution of copper sulphate changes into a green coloured solution.

The change of colour of the solution front blue to green is due to the formation of iron sulphate, a new substance. The brown substance deposit on the iron nail is copper, another new substance. We can write the reaction as:

Copper Sulphate solution (blue) + Iron → Iron Sulphate solution (green) + Copper (brown deposit).

Question 2.
What happens when carbon dioxide is passed through lime water? Give chemical equation.
Answer:
When carbon dioxide is passed through lime water, calcium carbonate is formed, which makes lime water milky. The turning of lime water milky is a standard test of presence of carbon dioxide.

Carbon dioxide (CO₂) + Lime water[Ca(OH)₂] → Calcium Carbonate(CaCo₃) + Water(H₂O)

Question 3.
What does ozone do for us?
Answer:
It protects us from the harmful ultraviolet radiations which come from the sun. Ozone absorbs this radiation and breaks down to oxygen.

If ultraviolet radiations were not absorbed by ozone, they would reach the earth’s surface and cause harm to us and other life forms. Ozone acts as a natural shield against these radiations.

Question 4.
Why has a fraction of ships iron to be replaced every year?
Answer:
Ships are made of iron and a part of them remains underwater. On the part above water also, water drops keep clinging to the ship’s outer surface. Moreover, the water of the sea contains many salts. The saltwater makes the process of rust formation faster. Therefore, ships suffer a lot of damage from rusting in spite of being painted. So much so, that a fraction of ship’s iron has to be replaced every year.

Physical and Chemical Changes Class 7 Extra Questions Long Answer Type

Question 1.
What happens when baking soda is added to vinegar and the resulting gas is passed through lime water?
Answer:
On adding baking soda to vinegar, a hissing sound is heard and bubbles are seen coming out. When this gas is passed through lime water, it turns milky.

The change in the test tube is as follows:
Vinegar (Acetic acid) + Baking soda (Sodium hydrogen carbonate) → Carbon dioxide + other substances

The reaction between carbon dioxide and lime water is as follows:
Carbon dioxide (CO₂) + Lime water [Ca(OH)₂] → Calcium Carbonate (CaC0₃) + Water (H₂0)

When carbon dioxide is passed through lime water, calcium carbonate is formed, which makes lime water milky. The turning of lime water milky is a standard test of carbon dioxide.

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