Lesson: Physical and Chemical Changes

Multiple choice questions

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

Solution:

d

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

Solution:

b

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

Solution:

d

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

Solution:

c

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)

Solution:

d

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.

Solution:

d

Question: 7

Galvanisation is a process used to prevent the rusting of which of the following?

(a)   Iron

(b)   Zinc

(c)   Aluminium

(d)   Copper

Solution:

a

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 – MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaieaaju gGbabaaaaaaaaapeGaa83eGaaa@3978@

(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.

Solution:

a

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.

Solution:

a

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

Solution:

c

Very Short Question Answers

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.

Solution:

(a)      True

(b)      True

(c)      True

(d)      False

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.

Solution:

Melting of wax is a physical change and is reversible, where a solid changes to a liquid state. Similarly, melting of ice too is a physical change and is also a reversible change, which converts solid into liquid.

Question: 13

What kind of change is shown by tearing of paper?

Solution:

Tearing of paper is a physical and irreversible change because there is no change in the property of paper and it cannot be reversed too.

Short Answers Questions

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

(e)   Iron oxide

(v)   Chemical change

(f)    Dissolving common salt in water

(vi)  Galvanisation

Solution:

Column I

Column II

(a)   Large crystals

(iv) Sugar candy

(b)   Depositing a layer of zinc on iron

(vi) Galvanisation

(c)   Souring of milk

(v)   Chemical change

(d)   Carbon dioxide

(i)      Turns lime water milky

(e)   Iron oxide

(iii)             Rust

(f)    Dissolving common salt in water

(ii)  Physical change

Question: 15

Fill in the blanks in the following statements using the words given in the box.

(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.

Solution:

(a)      Physical

(b)      Reversible

(c)      Physical

(d)      Rusted, chemical, substance

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.

Solution:

(i)          Physical change

(ii)       Chemical change

(iii)     Physical change

(iv)      Chemical change

Question: 17

Write word equations for two chemical reactions with the help of materials given in the box.

Solution:

(1)      Iron + Air + Water → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@  Iron oxide

(2)      Copper sulphate + Iron → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@  Iron sulphate + Copper

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.

Solution:

(a)      Lime water turns milky on passing carbon dioxide gas through lime water due to the formation of calcium carbonate.

Carbon dioxide (CO2) + Lime water [Ca(OH)2] → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@  

Calcium carbonate (CaCO3) + Water (H2O)

(b)      Bubbles are produced when acetic acid is added to a solution of sodium hydrogencarbonate due to the evolution of carbon dioxide gas which bubbles through the solution.

Vinegar (acetic acid) + Baking soda (sodium hydrogencarbonate) → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@   

Carbon dioxide + other substances

Long Answer Questions

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.

Solution:

(a)      Physical, reversible changes - melting of ice, folding of a sheet of paper

(b)      Physical, irreversible changes - breaking of glass, cutting of a log of wood into pieces

(c)      Chemical changes- digestion of food, burning of crackers

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.

Solution:

(a)      Copper sulphate solution (blue) + Iron → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@  

Iron sulphate solution (green) + Copper (brown deposit)

(b)      Vinegar (acetic acid) + Baking soda (sodium hydrogencarbonate) → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@

Carbon dioxide (gas) + other substances

(c)      Burning of crackers

 

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.

Solution:

(a)      Yes

(b)      No. Rusting of iron is a chemical and irreversible change.

(c)      Yes. Formation of rust is a new substance formed from iron which has new properties.

(d)      Setting of curd from milk, photosynthesis

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.

Solution:

(a)      The change of colour of the solution from blue to green due to the formation of iron sulphate, which is a new substance, and a brownish deposit on the iron nail.

(b)      Yes, these changes are chemical in nature, as new substances are forming with completely different chemical properties.

(c)      Copper sulphate solution (blue) + Iron → MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqGHsg IRaaa@3998@

Iron sulphate solution (green) + Copper (brown deposit)