Changes Around Us

Samacheer Book Back Questions And Answers For Science Standard 8 “Changes Around Us“

I. Choose the best answer:
1. Burning of paper is a _____ change.
a) physical
b) chemical
c) physical and chemical
d) neutral

2. Burning of matchstick is an example for chemical reaction caused by _____.
a) contact in physical states
b) electricity
c) light
d) catalyst

3. _____ undergoes rusting.
a) Tin
b) Sodium
c) Copper
d) Iron

4. The pigment responsible for browning of apples is _____.
a) hydrated iron (II) oxide
b) melanin
c) starch
d) ozone

5. Brine is a concentrated solution of _____.
a) sodium sulphate
b) sodium chloride
c) calcium chloride
d) sodium bromide

6. Limestone contains _____ mainly.
a) calcium chloride
b) calcium carbonate
c) calcium nitrate
d) calcium sulphate

7. Which of the following factor induces electrolysis?
a) Heat
b) Light
c) Electricity
d) Catalysis

8. In Haber’s process of producing ammonia _____ is used as a catalyst.
a) nitrogen
b) hydrogen
c) iron
d) nickel

9. Dissolved gases like sulphur dioxide and nitrogen oxides in rain water causes _____.
a) acid rain
b) base rain
c) heavy rain
d) neutral rain

10. _____ is/are responsible for global warming.
a) Carbon dioxide
b) Methane
c) Chlorofluorocarbons
d) Carbon dioxide, Methane, Chlorofluorocarbons

II. Fill in the blanks:
1. Photosynthesis is a chemical reaction that takes place in the presence of _____.
2. Iron objects undergo rusting when exposed to _____ and _____.
3. _____ is the basic material to manufacture urea.
4. Electrolysis of brine solution gives _____ & _____ gases.
5. _____ is a chemical substance which alters the speed of a chemical reaction.
6. _____ is the enzyme responsible for browning of vegetables and fruits.

Answers:
1. sunlight
2. water and oxygen
3. Ammonia
4. chlorine and hydrogen
5. Catalyst
6. Poly phenol oxidase or tyrosinase

III. Say true or false. If false, correct the statement:
1. A chemical reaction is a temporary reaction.
2. Decomposition of lead nitrate is an example for a chemical reaction caused by light.
3. Formation of slaked lime from quicklime is an endothermic reaction.
4. CFC is a pollutant.
5. Light energy may come out due to chemical reactions.

Answers:
1. False (A chemical reaction is permanent)
2. False (Decomposition of lead nitrate is an example for a chemical reaction based on heat)
3. False (Formation of slaked limed from quicklime is a exothermic reaction)
4. True
5. True

IV (A). Match the following:
1. Rusting            A. Photosynthesis
2. Electrolysis       B. Haber’s process
3. Thermolysis      C. Iron
4. Food                 D. Brine
5. Catalysis           E. Decomposition of limestone

Answers:
1. C
2. D
3. E
4. A
5. B

IV (B). Match the following:
1. Spoilage            A. Decomposition
2. Ozone                B. Biocatalyst
3. Tarnishing          C. Oxygen
4. Yeast                  D. Chemical reaction
5. Calcium oxide    E. Food

Answers:
1. E
2. C
3. D
4. B
5. A

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