NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes are provided here with simple step-by-step explanations. These solutions for Physical And Chemical Changes are extremely popular among Class 7 students for Science Physical And Chemical Changes Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 7 Science Chapter 6 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 33:
Question 1:
Which of the following is a physical change?
(a) Rusting of iron
(b) Combustion of magnesium ribbon
(c) Burning of candle
(d) Melting of wax
Answer:
A change in which a substance undergoes a change in its physical properties is called a physical change. No new substances are formed in such changes. Melting of wax is an example of physical change.
Hence, the correct answer is option (d).
Page No 33:
Question 2:
Which of the following is a chemical change?
(a) Twinkling of stars
(b) Cooking of vegetables
(c) Cutting of fruits
(d) Boiling of water
Answer:
A change in which one or more new substances are formed is called as a chemical change. Cooking of vegetables is an example of a chemical change.
Hence, the correct answer is option (b).
Page No 33:
Question 3:
A chemical change may involve –
(a) change in colour only
(b) change in temperature only
(c) evolution of gas only
(d) any or all of the above
Answer:
A chemical change may involve change in colour, temperature, smell or evolution of gas, heat, etc.
Hence, the correct answer is option (d).
Page No 33:
Question 4:
Which of the following is/are true when milk changes into curd?
(i) Its state is changed from liquid to semi solid.
(ii) It changes colour.
(iii) It changes taste.
(iv) The change cannot be reversed.
Choose the correct option from below :
(a) (i) and (ii) are correct
(b) (ii) and (iii) are correct
(c) (i), (iii) and (iv) are correct
(d) (i) to (iv) are correct
Answer:
When milk changes to curd it becomes semi solid. The taste of milk changes and the change cannot be reversed i.e., we cannot change curd to milk. However, no color change is involved in the process as it remains white.
Hence, the correct answer is option (c).
Page No 33:
Question 5:
A man painted his main gate made up of iron, to
(i) prevent it from rusting.
(ii) protect it from sun.
(iii) make it look beautiful.
(iv) make it dust free.
Which of the above statement(s) is/are correct?
(a) (i) and (ii)
(b) (ii) and (iii)
(c) only (ii)
(d) (i) and (iii)
Answer:
Painting is done on gates made up of iron to prevent rusting and make it look more beautiful.
Hence, the correct answer is option (d).
Page No 34:
Question 6:
Iron pillar near the Qutub Minar in Delhi is famous for the following facts. Which of these facts is responsible for its long stability?
(a) It is more than 7 metres high.
(b) It weighs about 6000 kg.
(c) It was built more than 1600 years ago.
(d) It has not rusted after such a long period.
Answer:
Iron pillar near Qutub Minar in Delhi is famous for its stability because it has not rusted over a long period.
Hence, the correct answer is option (d).
Page No 34:
Question 7:
Galvanisation is a process used to prevent the rusting of which of the following?
(a) Iron
(b) Zinc
(c) Aluminium
(d) Copper
Answer:
In the process of galvanisation, iron is coated with zinc to prevent its rusting.
Hence, the correct answer is option (a).
Page No 34:
Question 8:
Paheli’s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This indicates a –
(a) physical change that can be reversed.
(b) chemical change that can be reversed.
(c) physical change that cannot be reversed.
(d) chemical change that cannot be reversed.
Answer:
Mixing of sugar in water is a physical change and crystals of sugar can be separated on cooling, therefore, it is a reversible change.
Hence, the correct answer is option (a).
Page No 34:
Question 9:
Which of the following statement is incorrect for a chemical reaction?
(a) Heat may be given out but never absorbed.
(b) Sound may be produced.
(c) A colour change may take place.
(d) A gas may be evolved.
Answer:
When a chemical reaction takes place, heat may be given out or absorbed, sound may be produced, color change may take place and a gas may be evolved.
Hence, the correct answer is option (a).
Page No 34:
Question 10:
Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and then small amount of hot water was added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and step II are:
(a) physical and chemical changes respectively.
(b) chemical and physical changes respectively.
(c) both physical change.
(d) both chemical change.
Answer:
Dissolution of copper sulphate powder in water in presence of sulphuric acid is a physical change. On cooling this hot solution, the crystals of copper sulphate are separated which is also a physical change.
Hence, the correct answer is option (c).
Page No 35:
Question 11:
State whether the following statements are true or false:
(a) When a candle burns, both physical and chemical changes take place.
(b) Anaerobic bacteria digest animal waste and produce biogas.
(c) Ships suffer a lot of damage though they are painted.
(d) Stretching of rubber band is not a physical change.
Answer:
(a) True
(b) True
(c) True
(d) False, stretching of rubber band is a physical change.
Page No 35:
Question 12:
Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings.
Answer:
The examples of changes observed in surroundings in which a solid changes to liquid state are melting of ice, melting of butter etc.
Page No 35:
Question 13:
What kind of change is shown by tearing of paper?
Answer:
Tearing of paper is a physical change as only the appearance of the paper changes and no new substances are formed in this change.
Page No 35:
Question 14:
Match the items of Column I with the items of Column II.
| Column I | Column II |
| (a) Large crystals | (i) Turns lime water milky |
| (b) Depositing a layer of zinc on iron | (ii) Physical change |
| (c) Souring of milk | (iii) Rust |
| (d) Carbon dioxide | (iv) Sugar candy (mishri) |
| (e) Iron oxide | (v) Chemical change |
| (f) Dissolving common salt in water | (vi) Galvanisation |
Answer:
The correct match between column I and column II is given as:
(a) - (iv)
(b) -(vi)
(c) - (v)
(d) - (i)
(e) - (iii)
(f) - (ii)
Page No 36:
Question 15:
Fill in the blanks in the following statements using the words given in the box.
rusted, colourful, substance, chemical, physical, reversible, iron oxide, object
(a) Making sugar solution is a ____________ change.
(b) A physical change is generally____________.
(c) Grinding of wheat grain changes its size. It is a ____________ change.
(d) Iron benches kept in lawns and gardens get____________. It is a _________ change because a new _________ is formed.
Answer:
(a) Making sugar solution is a physical change.
(b) A physical change is generally reversible.
(c) Grinding of wheat grain changes its size. It is a physical change.
(d) Iron benches kept in lawns and gardens get rusted. It is a chemical change because a new substance is formed.
Page No 36:
Question 16:
Classify the following processes into physical or chemical changes:
(i) Beating of aluminium metal to make aluminium foil.
(ii) Digestion of food.
(iii) Cutting of a log of wood into pieces.
(iv) Burning of crackers.
Answer:
(i) Physical change
(ii) Chemical change
(iii) Physical change
(iv) Chemical change
Page No 36:
Question 17:
Write word equations for two chemical reactions with the help of materials given in the box.
Air, copper sulphate, iron, vinegar, iron oxide, carbon dioxide, iron sulphate, copper, lime water, water
Answer:
The two word equations can be written as:
1. Iron + Air + Water → Iron oxide
2. Copper sulphate + Iron → Iron sulphate + Copper
Page No 36:
Question 18:
Explain the following:
(a) Lime water turns milky on passing carbon dioxide gas into it.
(b) Bubbles are produced when acetic acid is added to a solution of sodium hydrogencarbonate.
Answer:
(a) When carbon dioxide gas is passed through lime water, it turns milky because a white precipitate of calcium carbonate is formed. The word equation can be represented as:
Calcium hydroxide + Carbon dioxide →Calcium carbonate + Water
(b) When acetic acid is added to a solution of sodium hydrogen carbonate, carbon dioxide gas is formed which comes out in the form of bubbles.The word equation can be represented as:
Sodium hydrogen carbonate + Acetic acid → Sodium carbonate + Water + Carbon dioxide
Page No 36:
Question 19:
Give two examples for each of the following cases:
(a) Physical changes which are reversible.
(b) Physical changes which are not reversible.
(c) Chemical changes.
Answer:
(a) Folding of paper and melting of ice are the examples for physical changes which are reversible.
(b) Cutting of paper and breaking of glass are the examples of physical changes which are not reversible.
(c) Rusting of iron and curdling of milk are the examples for chemical changes.
Page No 37:
Question 20:
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.
Answer:
(a) Reaction between copper sulphate and iron metal – blue solution of copper sulphate changes to green solution of ferrous sulphate.
(b) Reaction between Sodium hydrogen carbonate and acetic acid – carbon dioxide gas is evolved.
(c) Burning of crackers produces a loud sound.
Page No 37:
Question 21:
If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.
(a) Do you think rust is different from iron?
(b) Can you change rust back into iron by some simple method?
(c) Do you think formation of rust from iron is a chemical change?
(d) Give two other examples of a similar type of change.
Answer:
(a) Rust is a reddish brown powder of iron oxide and hence, it is different from iron.
(b) No. Rusting of iron is a chemical change and irreversible in nature.
(c) Yes. Rusting of iron is a chemical change as new substance i.e., iron oxide is formed.
(d) Two examples of similar type of changes are:
(i) Burning of magnesium ribbon to give magnesium oxide.
(ii) Burning of wood to give coal and ash.
Page No 37:
Question 22:
A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour.
(a) What changes do you expect?
(b) Are these changes chemical in nature?
(c) Write a word equation for the chemical change, if any.
Answer:
(a) Copper sulphate solution is blue in colour. When an iron nail is left in it for some time the blue colour of copper sulphate solution changes to green due to the formation of ferrous sulphate and the surface of iron nail gets a brown coloured deposit.
(b) Yes, the changes are chemical changes because new substances iron sulphate and copper are formed in the reaction.
(c) Copper sulphate + Iron → Iron sulphate + Copper
(Blue) (Grey) (Green) (Brown)
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