CHAPTER- PHYSICAL AND CHEMICAL CHANGES

Ch-6 Physical and Chemical Changes
Focus words

1. Physical Change: The change in which no new substance is
formed but only physical properties like shape, size, colour of
the substance changes.
Ex: Cutting of paper.

2. Chemical Change: The change in which new substances are
formed is called a chemical change.

Ex: Burning of paper.
3. Chemical reaction: The process in which one or more
substances ( reactants) combine together and form new
substances ( products) with different properties is called chemical
reaction.

Ex: Photosynthesis is a chemical reaction.

4. Crystallisation: The process of separation of a solid crystal
from its solution by boiling or evaporation is called crystallization.

5. Galvanisation: The process of deposition of a layer of zinc
metal over the iron with the help of electricity is called
galvanisation.

6. Rusting: The process in which iron combines with oxygen in
presence of moisture ( water vapour) and form brownish powder
that is rust.

2Fe +O2 +xH2O --- Fe2O3+xH2O

7. Electroplating: The process of coating ( deposition) a
layer superior metal over another metal with the help of
electricity.

Ex: electroplating of gold over copper metal.

8. Saturated solution: The solution in which no more solute
can be dissolved is called saturated solution.
9. Displacement reaction: The reaction in which one more
reactive metal displaces another less reactive metal from its
salt solution is called displacement reaction.

Ex:

Fe+CuSO4 --- FeSO4 +Cu

10. Compound: The chemical substance which is formed
when two or more elements combine chemically in a fixed ratio
by mass.

CHAPTER 10
RESPIRATION IN
ORGANISMS

NCERT QUES ANS

QUE 1. Why does an athlete breathe faster and deeper than usual
after finishing a race?
Ans. An athlete breathes faster and deeper than usual after finishing
a race, because he needs extra energy. So he takes deep breathe to
inhale more oxygen.

Que2. List similarities and difference between aerobic and anaerobic
respiration.

Ans. SIMILARITIES:- 1. In both the type of respiration,
breakdown of food takes place.
2. Energy is released in both respirations.

DIFFERENCE:- Anaerobic Respiration

Aerobic Respiration 1. Breakdown of glucose occurs
1. Breakdown of glucose without the help of oxygen.
occurs with the help of 2.Glucose breakdown into
oxygen. 2.Glucose alcohol, CO2 and H2O.
breakdown into CO2, H2O and
energy.

Que3 Why do we often sneeze when we inhale a lot of dust
laden air?

Ans. The air around us has many types of unwanted particles such as
smoke, dust, pollens etc. When we inhale, the particles get trapped in
the hair present in our nasal cavity. However, sometimes these
particles may get past the hair in the nasal cavity. Then they irritate
the lining of the cavity, as a result of which we sneeze. Sneezing
expels

these foreign particles from the inhaled air and a dust free clean
air enters our body.

Que4 Take three test tubes---------------------- concentration of CO2 ?

Ans. Test tube A will contain highest concentration of CO2 because it
contains snail which exhale CO2.

Que5 Tick the correct answers.

a. Spiracles

b. Lactic acid

c. 15-18

d. move downwards

Que6 Match the

column

Column I Column II

Yeast Alcohol

Diaphragm Chest cavity

Skin Earthworm

Leaves Stomata

Fish Gills

Frog Lungs and Skin

Que7 True / False

1. False

2. False

3. True

4. False
5. True
Que8 Give one word for following
1. Trachea
2. Ribs
3. Diaphragm
4. Stomata
5. Spiracles
6. Lungs
7. Nostrils
8. Yeast
9. Ant
Que9 The mountaineers carry oxygen with them because
Ans. The amount of air available to a person is less than that
available on the ground.

CHAPTER 6
PHYSICAL AND CHEMICAL CHANGES

EXTRA QUE/ ANS

Que 1: Define rusting of iron with reaction.

Ans: If we leave a piece of iron in the open for some time, it acquires
a film of brownish substance. This substance is called rust and this
process is called rusting.

Reaction:- 4Fe + 3O2 + 2H2O --- 2Fe2O3 . 2H2O

(Iron) (Oxygen) (Water) Rust(Iron oxide)

For rusting, the presence of both oxygen and water (or water vapour) is
essential.

Que2: What are the different methods of preventing rusting of iron?

Ans: Different methods of preventing rusting of iron are listed below:-
1. By painting
2. By greasing
3. By galvanisation
4. By alloying

Que3 : Define galvanization. Give one use of it.

Ans: The process of depositing a layer of zinc on iron is called
galvanization.

USES: The iron pipes we use in our homes to carry water are
galvanized to prevent rusting.

Que4. Write down the chemical reaction between vinegar and baking
soda.

Ans Vinegar + Baking Soda---- CO2 + Other Substances

(Acetic Acid) (Sodium Bicarbonate) (Carbon dioxide)

Que5. What happens when iron nail is dropped in copper sulphate

solution? What type of change is it?

Ans: When iron nail is dropped in copper sulphate solution, Chemical

change takes place. The colour of the solution changes from blue to

green due to the formation of iron sulphate and there is a brown deposit

of copper on iron nail.

Reaction : Fe + CuSo4 ------ FeSO4 + Cu

(Iron) (Copper sulphate) (Iron sulphate) (Copper)

(Blue) (Green)

Que6. Explain how following are chemical change.

Ans: 1. Burning of a substance:- Burning of a substance is a
chemical change because during burning, new substance like
carbon dioxide , ash etc. are formed with the production of heat.

2. Explosion of fire cracker :- Explosion of a firework is a chemical
change because explosion produces heat , light , sound and unpleasant
gases that pollute the atmosphere which are new substance.

3. Spoiling of food :- It is a chemical change because when food gets
spoiled, it produces a foul smell with the formation of new substances.

4. A slice of an apple acquires brown color:- It is a chemical change
because a slice of an apple acquires brown color due to the formation of
new substances.

5. Neutralisation :- It is a chemical change because in neutralization, an
acid reacts with base to form new substances like salt and water with
the production of heat.

Que7 . Define Physical and Chemical change.

Ans Physical change :- A change in which a substance undergoes a
change in its physical properties like shape , size , state etc is called a
physical change. In such a change no new substance is formed.
Example:- Melting of ice , Melting of wax , Tearing of paper , Boiling
of wateretc.

Chemical change :- A change in which one or more new substances
are formed is called a chemical change. A chemical change is called
irreversible change.

Example:- spoiling of food , burning of wood , formation of curd etc.

Que8. Differentiate between chemical and physical changes.

Ans:

Physical changes Chemical changes

1. No new substance is formed. 1. New substance is formed.
2. It is a temporary change. 2. It is a permanent change.
3. It is generally reversible. 3. It is generally irreversible.
4. Very little energy is obtained 4. A lot of energy is absorbed or
or given out in this change. given out.

Que9. Give standard test of the evolution of carbon dioxide with the

help of reaction.

Ans: When carbon dioxide is passed through lime water, calcium
carbonate is formed, which makes lime water milky. The turning of lime
water into milky is a standard test of carbon dioxide.
Reaction : Carbon dioxide + lime water --- Calcium carbonate

+ water(CO2) [Ca(OH)2] (CaCO3)

(H2O)

Que10. What is rust? Give example.

Ans: If we leave a piece of iron in the open for some time, it acquires
a film of brownish substance. This substance is called rust.
For Example: 1. Iron gates of parks or farm lands, iron benches kept
in lawns and gardens , almost every article of iron , kept in open gets
rusted.

2. Shovels and spades get rusted when exposed to the atmosphere for
some time.

3. In the kitchen , a wet iron pan (tawa) often gets rusted if left in that state
for some time.

Que11: Give an activity to show that burning of magnesium ribbon is
a chemical change.

Ans: Activity:

1. Take a small piece of a thin strip or ribbon of magnesium.

2. Clean its tip with sand paper.

3. Bring the tip near a candle flame.

4. It burns with a brilliant white light.

5. When it is completely burnt it leaves behind a powdery ash.

Reaction:- 2Mg + O2 ---- 2MgO

(Magnesium) (Oxygen) (White powdery ash)

The magnesium oxide formed is a new substance. So, burning of
magnesium ribbon is a chemical change.

Que12: In addition to new substance what may accompany a chemical
change?

Ans: In addition to new products, the following may accompany a
chemical change.
1. Heat, Light or any other radiation (ultraviolet for example) may be given
off or absorbed.
2. Sound may be produced.
3. A change in smell may take place or a new smell may be given off.
4. A color change may takes place.
5. A gas may be formed.

Que13: Define crystallization. What type of change is it?

Ans: Crystallization :- The process of obtaining pure crystals of a
new substance from the solution is called crystallization. It is a
physical change.

Que14. What is stainless steel? How it is made?

Ans: Stainless steel is an alloy of iron. Stainless steel is made by
mixing iron with carbon and metals like chromium, nickel and
manganese. It does not rust.

Que15. Can we call a breaking down of O3 (ozone) is a chemical
change.

Ans: Yes, breaking down of ozone is a chemical change because Ozone
allows ultraviolet radiations and breakdown to oxygen. Oxygen is different
from ozone.

Ultraviolet

Reaction:- 2O3 -------------------------------- 3O2

Radiation

Assignment No. 10
Chapter — 6 Physical& Chemical

Change

I. Write One word for the following:
1. Prevention of rusting of iron by coating it with zinc. G ALVANIS ATION
2. The process in which a metal is displaced by a more reactive metal.
DISPLACEMENT REACTION
3. A change in which only the physical properties of any substance getchanged.
PHYSICAL CHANGE

4. A change which is irreversible, permanent and leads to the formation of one or

more new substances. CHEMICAL CHANGE

II Fill in the blanks
1. Changes can be of two types, Physical and Chemical -

2. Physical changes are changes in physical properties of a substance.

3. Inchemical change new substances are produced. .

4. Some substances can be obtained in pure state from their solutions by crystallization

5. Theprocessof depositing alayerof zinc on iron iscalled galvanisation

6. Growth of plantsis a chemical change.

7. Melting of wax is a physical change.

8. Thechemical nameofrustis hydrated ironoxide

9. Dissolution of carbon di-oxide gas in water is a physical change.

10. Magnetisation of an iron piece is a physical change.

III Match the following. B
A i) Burning of carbon( d )

a) Neutralisation reaction ii) Formation
ofcarbondioxide when
b) Displacement reaction baking soda is heated(

c )
c) Decomposition reaction iii) Deposition of copper when an iron nail is

d) Combination reaction placed in copper(II) solution.( b )

IV Multiple Choice iv) Formation of NaCI and H Owhen HCI reacts
questions. with sodium hydroxide ( a ).

Identify change while formation of curd from milk is

(a) Physical change (b) Chemical change (c) None of these

2. This is a Physical Change.

(a) Boiling of (c) All of above

water

(b) Rusting (c) All of above

3. A physical change

involves change in

(a)shape, size (b)
colours
(c) CaCO3

4. The effervescence is

due to release of
(a) Ca(OH )2

(b)CO2
5. Formula of calcium
carbonate is

(a) Ca OH) (b)C

2

6. Carbondioxide can be
testedusing

(a) Chemical change (b) Physical Change (c) None of these
7. Explosion of a firework produces- -

(a) Heat & Light (b) Heat only. (c) Gases only. (d) Heat, light, sound & unpleasantgases.

8. Galvanisation is a process of coating iron metal with

(a) Zinc (b) Magnesium (c) Tin

9. Rusting results in

(a)Loss ofmetal (b) No loss of metal (c) Gain of Fe
10. Rusting is a

(a) slow (c) Average Process
process
(b) Fast process

11. What is colour of

copper sulphate

solution

(a) yellow (b)Blue (c) White

12. What is the brown coloured substance formed in the reaction between iron

and copper sulphate.

(a) Rust (b) Cu (d) Fe

13. Crystallisation is a

type of

(a) Chemical change (b)Physical Change (c) Bio- Chemical Change

14. Lime water turns milky when gas is passed through it.

(a) Carbon dioxide (b) Hydrogen

(c) Oxygen (d) Nitrogen dioxide

15. The process of obtaining pure crystals of copper sulphate from copper sulphate

solution is known as-
(a) Galvanization
(c) Crystallization (b) Evaporation

16. Baking soda is common (d) Rusting

name for- - (d) Sodium hydrogen carbonate

(a) Sodium carbonate (d) Sodium hydroxide

(c) Calcium carbonate

17. Blue vitriol is the

common name of -

(a) Copper sulphate (b) Copper oxide

(c) Copper hydroxide (d) Magnesiumsulphate

18. The elements required for rusting of iron.

(a)Oxygen and moisture (b) Only oxygen

(c) Hydrogen and oxygen (d) Only water vapours.