In this page, we are providing Physical and Chemical Changes Class 7 Extra Questions and Answers Science Chapter 6 pdf download. NCERT Extra Questions for Class 7 Science Chapter 6 Physical and Chemical Changes with Answers will help to score more marks in your CBSE Board Exams.
Class 7 Science Chapter 6 Extra Questions and Answers Physical and Chemical Changes
Extra Questions for Class 7 Science Chapter 6 Acids, Bases and Salts with Answers Solutions
Physical and Chemical Changes Class 7 Extra Questions Very Short Answer Type
Question 1.
What is the colour of the flame when magnesium is burnt?
Answer:
White
Question 2.
What kind of change is rusting?
Answer:
Chemical
Question 3.
Define galvanisation.
Answer:
The process of depositing a layer of zinc over iron is called galvanisation.
Question 4.
What is the meaning of rusting?
Answer:
The formation of rust over the surface of iron is known as rusting.
Question 5.
State two examples of physical changes.
Answer:
(i) Cutting a piece of paper
(ii) Melting of ice
Question 6.
Name the two main kinds of changes.
Answer:
- Physical
- Chemical
Question 7.
State the decomposition of calcium carbonate with the help of formulae and chemical reactions.
Answer:
Question 8.
Which gas is released when baking soda is mixed with vinegar?
Answer:
Carbon dioxide (Co2)
Question 9.
Name the ultimate colour of the solution when iron nails are dipped in the solution of copper sulphate.
Answer:
Green
Question 10.
What is the nature of aqueous solution of magnesium oxide?
Answer:
The aqueous solution of magnesium oxide is basic in nature, as it turns red litmus blue.
Question 11.
Define rust.
Answer:
Rust is a red or brown oxide coating on iron caused by the action of oxygen and moisture.
Question 12.
Is burning a physical change?
Answer:
No
Question 13.
Name the colour of copper sulphate solution.
Answer:
Blue
Question 14.
What type of change occur when iron reacts with copper sulphate?
Answer:
Chemical change
Question 15.
Name two important factors responsible for rusting.
Answer:
- Water (or moisture)
- Oxygen
Physical and Chemical Changes Class 7 Extra Questions Short Answer Type
Question 1.
Define crystallisation.
Answer:
The process of obtaining pure crystals of substances from their solution is called crystallisation.
Question 2.
What happens when carbon dioxide passes through lime water?
Answer:
When carbon dioxide passes through lime water, calcium carbonate is formed and lime water turns milky.
Question 3.
Name some physical properties of a substance.
Answer:
Shape, size, colour, state of a substance are some of its physical properties.
Question 4.
Give some examples of physical changes.
Answer:
Following are some examples of physical changes:
- Melting of ice
- Glowing of electric bulb
- Change of water into steam
- Cutting of a block of wood
- Breaking of a glass tumbler
Question 5.
Give some examples of chemical changes.
Answer:
Following are some examples of chemical changes:
- Curdling of milk
- Burning of a piece of paper
- Cooking of rice
- Rusting of iron
- Explosion of firecrackers
Question 6.
Explain the burning of magnesium ribbon.
Answer:
Take a thin ribbon of magnesium. Gently clean the end of the ribbon with sand paper and bring its tip near a candle flame. It is observed that the ribbon burns with a bright white light. After combustion, white powdery ash is left, which is called magnesium oxide.
Question 7.
Define chemical change. Give one example.
Answer:
A change in which one or more new substance(s) is/are formed is called a chemical change; e.g., burning of a matchstick.
Question 8.
What do you mean by physical change?
Answer:
A change in which a substance undergoes a change in its physical properties is called a physical change.
Question 9.
What are the characteristics of a chemical change?
Answer:
The characteristics of a chemical change are:
- They release or absorb energy.
- Most of the changes are irreversible.
- One or more new substances with new properties are formed.
- The properties of products are entirely different from the reactants.
Question 10.
Write some points about ozone layer.
Answer:
- It acts as a shield against the harmful radiations of the sun.
- Its chemical formula is o3.
- Ozone is entirely different from oxygen.
Physical and Chemical Changes Class 7 Extra Questions Long Answer Type
Question 1.
Why is the burning of a candle considered a chemical change?
Answer:
Candles are made of wax and a long thread of cotton (called wick of the candle). While candle is burnt, the molten wax goes up through the thread and undergoes combustion to form carbon dioxide and water vapour. The ‘wick’ of the candle gets changed to a black mass.
Over the process, heat and light energy is given out. It is not possible to
(i) recover the burnt wax again,
(ii) recover the thread again.
Hence, the burning of a candle is a chemical change.
Question 2.
State the differences between chemical and physical changes.
Answer:
| Chemical change | Physical change |
| (i) It is generally a irreversible process. | (i) It is generally a reversible process. |
| (ii) A new substance is formed. | (ii) No new substance is formed. |
| (iii) Properties of a substance changes. | (iii) Properties of a substance does not changes. |
| (iv) Energy is given out or absorbed during the change. | (iv) No energy is given out or absorbed during the change. |
Question 3.
What happens when iron nails are dipped in copper sulphate solution?
Answer:
When iron nails are dipped in copper sulphate solution, a brown layer of copper gets deposited on the surface of iron nails after some time. This happens due to the reaction between copper sulphate and iron. Also, the colour of copper sulphate changes from blue to green due to the formation of iron sulphate.
Question 4.
Most of the physical changes are reversible but some are irreversible. Explain the statement with examples.
Answer:
In physical change, a substance undergoes a change in its physical properties only. Physical change occurs when there is a force applied, change in temperature, etc., on a substance. Most of the physical changes are reversible like rolling a dough into a chapati and then again bringing back into a dough.
Making a toy aeroplane by folding the paper and then again unfolding the toy aeroplane to recover the page. But when a physical change cannot be reversed or we cannot bring the substance back to its original shape, size, state, etc., is known as irreversible change. For example, baking chapati or making a toy aeroplane by cutting the paper instead of folding it.
Question 5.
Give an example of a chemical reaction for each of the following situations:
(a) A change in colour is observed.
(b) A gas is evolved.
(c) Sound is produced.
(d) Heat is produced.
(e) Change in taste is observed.
(f) Light is produced.
Answer:
(a) Reaction between copper sulphate solution and iron metal. Blue colour of copper sulphate solution changes to green colour ferrous sulphate solution.
(b) Reaction between baking soda and vinegar evolves carbon dioxide gas.
(c) Burning of crackers produces sound.
(d) Reaction between hydrochloric acid and sodium hydroxide produces heat.
(e) Setting of curd from milk. Taste of milk changes to sour in curd.
(f) Burning of fuel produces light.
Physical and Chemical Changes Class 7 Extra Questions HOTS
Question 1.
When we keep a piece of iron in the open area for few days, a brownish, flaky substance, called rust, is deposited on it.
(a) Is rust different from iron?
(b) Is formation of rust from iron a chemical change?
(c) Can you change rust back into iron by some simple method?
(c) Give some other examples of a similar type of changes.
Answer:
(a) Yes. Rust is oxide of iron.
(b) Yes, it is a chemical change as properties of iron has changed.
(c) No.
(d) 1. Setting of curd into milk.
2. Burning of magnesium ribbon in air.
3. Cooking of food.
Question 2.
Why lime water turns milky on passing carbon dioxide gas into it?
Answer:
Chemical formula of lime water is calcium hydroxide which is a colourless solution. When we pass carbon dioxide gas into lime water, it forms white coloured insoluble calcium carbonate.
Lime water + Carbon dioxide ➝ Calcium carbonate + Water
Question 3.
Why iron pillar in Qutub Minar in Delhi famous?
Answer:
It is famous because it has not rusted though was built more than 1600 years ago.
Physical and Chemical Changes Class 7 Extra Questions Value Based (VBQs)
Question 1.
Sarita while helping her mother in kitchen work noticed that the slices of potato and brinjal have acquired a brown colour. She asked her mother reason behind this change. Her mother said whenever we keep cut pieces of these vegetables open for long time they acquire such colour.
(a) Are cutting vegetables and change in colour, physical or chemical changes?
(b) Why vegetables acquired brown colour?
(c) Do this brown colouration indicate that the vegetables are spoilt. Can we reverse this process? Why?
(d) Can you suggest ways to avoid this colouration of vegetables?
(e) What value of Sarita is shown here?
Answer:
(a) Cutting vegetables is physical change and change in colour of vegetables is chemical change.
(b) Vegetables acquire brown colour due to chemical reaction and thus, formation of new substance.
(c) No, vegetables are not spoilt and we cannot reverse this process because it is a chemical change.
(d) 1. By not keeping cut vegetables for long time to exposed air.
2. By dipping cut vegetables in cold water.
(e) Sarita is helping in nature, thoughtful and inquisitive.
Question 2.
Ramesh and Shyam both bought a big iron table for their shop individually. Ramesh painted his table with paints whereas Shyam got it laminated.
(a) What conditions are necessary for the process of rusting?
(b) Whose method is effective in preventing rusting? How?
(c) How rusting cause a great economic loss?
(d) What values of Ramesh and Shyam are shown here?
Answer:
(a) For rusting, moisture and oxygen is necessary.
(b) Both, Ramesh’s and Shyam’s methods are effective in preventing rusting. Painting and lamination, both, will prevent air and moisture from coming in contact with the iron table.
(c) Rusting cause a great economic loss as replacement of corroded equipment, their maintenance,
A contamination of other substances, etc., requires a huge amount to be spent on them.
(d) Ramesh and Shyam are both intelligent and responsible.