Samacheer Kalvi 8th Science Book Back Answers Chapter 10

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Samacheer Kalvi 8th Science Book Back Question and Answers:

Samacheer Kalvi 8th Standard Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 8 New Syllabus 2022 to 2023 Book Back Questions & Answers/solutions available for both English and Tamil Medium. Class 8 std Science Book Chapter 10 – Changes around us Science Answers/Solutions Guide are uploaded on this page. 8th standard Science Book is consists of 23 Units. All 23 chapters of Science Book Back One, and Two Mark Solutions are given below.

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8th Science Book Back Chapter 10 Solutions Guide PDF:

Samacheer Kalvi 8th Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

8th Science Chapter – 10

Changes around us – Book Back Answers

 

I. Choose the best answer:

1. Burning of paper is a …………….. change.
(a) Physical
(b) Chemical
(c) Physical & chemical
(d) Neutral
Answer:
(b) Chemical

2. The burning of matchstick is an example for chemical reaction based on
(a) Contact
(b) Electricity
(c) Light
(d) Catalyst
Answer:
(c) Light

3. …………….. metal undergoes rusting.
(a) Tin
(b) Sodium
(c) Copper
(d) Iron
Answer:
(d) Iron

4. The pigment responsible for browning of apples is …………….
(a) Hydrated iron (II) oxide
(b) Melanin
(c) Starch
(d) Ozone
Answer:
(b) Melanin

5. Brine is a concentrated solution of ………………
(a) Sodium sulphate
(b) Sodium chloride
(c) Calcium chloride
(d) Sodium bromide
Answer:
(b) Sodium chloride

6. Limestone contains ………………. mainly.
(a) Calcium chloride
(b) Calcium carbonate
(c) Calcium nitrate
(d) Calcium sulphate
Answer:
(b) Calcium carbonate

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

8. In Haber’s process of producing ammonia is used as a catalyst.
(a) Nitrogen
(b) Hydrogen
(c) Iron
(d) Nickel
Answer:
(c) Iron

9. Dissolved gases like sulphur dioxide, nitrogen oxides in rain water causes
(a) Acid rain
(b) Base rain
(c) Heavy rain
(d) Neutral rain
Answer:
(a) Acid rain

10. …………….. is responsible for Global warming.
(a) Carbon di oxide
(b) Methane
(c) Chlorofluoro carbons
(d) All the above
Answer:
(a) Carbon di oxide

II. Fill in the blanks

  1. Photosynthesis is a chemical reaction that takes place in presence of Iron objects undergo rusting when exposed to and ……………..
  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, fruits.

Answer:

  1. Sunlight
  2. Water, oxygen
  3. Ammonia
  4. Chlorine and hydrogen
  5. Catalyst
  6. Poly phenol oxidase or tyrosinase




III. Write True Or False for the following

1. A chemical reaction is a temporary reaction.
Answer:
False.
Correct statement:
A chemical reaction is permanent.

2. Change in colour may take place during a chemical reaction.
Answer:
True.

3. Formation of slaked lime from quicklime is a endothermic reaction.
Answer:
False.
Correct statement:
Formation of slaked limed from quicklime is a exothermic reaction.

4. CFC is a pollutant.
Answer:
True.

5. Browning of some vegetables and fruits is due to tannin formation.
Answer:
False.
Correct statement:
Browning of some vegetables and fruits is due to melanin formation.




IV. Match the following

a.

                                 A                                             B
     1.      Rusting      (a)      photosynthesis
     2.      Electrolysis      (b)      Haber’s process
     3.      Thermolysis      (c)      Iron
     4.      food      (d)      Brine
     5.      Catalysis      (e)      Decomposition of limestone

Answer:

1 – c;  2 – d; 3 – e; 4 – a; 5 – b

b.

                                    A                                                      B
     1.      Rancidity      (a)      Decomposition
     2.      Ozone      (b)      biocatalyst
     3.     Tarnishing      (c)      oxygen
     4.      Yeast      (d)      chemical reaction
     5.      Calcium Oxide      (e)      fish

Answer:

1 – e; 2 – c; 3 – d; 4 – b; 5 – a

V. Give Short Answers For The Following Questions

1. Define a chemical reaction. .
Answer:
Chemical changes are otherwise called as chemical reactions, because one or more substances (Reactants) undergo a reaction to form one or more new substances (Products).
Reactant(s) → Product(s)

2. Mention the various conditions required for a chemical reaction to occur.
Answer:
The conditions required for a chemical reaction to take place:

  1. Physical contact
  2. Solution of reactants
  3. Electricity
  4. Heat
  5. Light
  6. Catalyst

3. Define catalysis.
Answer:
Chemical substance used to alters the speed of the reaction is called catalyst and the process is called catalysis.

4. What happens when an iron nail is placed in copper sulphate solution?
Answer:
When iron nail is dipped in the solution of copper sulphate, copper is displaced by iron and forms ferrous sulphate. Thus, the blue colour of copper sulphate changes into green because of formation of ferrous sulphate.

5. What is pollution?
Answer:
Unwanted change in physical, chemical and biological properties of the environment. This is termed as pollution.

6. What is Tarnishing? Give an example.
Answer:
Tarnishing of metal articles:
Shiny metal surfaces and other articles lose their shining appearance due to chemical reactions on the surface. For example, silver articles become black on exposure to atmospheric air.

Similarly, brass vessels which contain copper as one of constituents develop a greenish layer on exposure to air for a long time. This is due to a chemical reaction between copper and moist air to form basic copper carbonate and copper hydroxide.

7. What happens to the brine during electrolysis?
Answer:
A concentrated solution of sodium chloride called Brine is electrolysed to produce chlorine and hydrogen gases along with sodium hydroxide. This is a very important reaction to produce chlorine industrially.

8. On heating, calcium carbonate gives calcium oxide and oxygen. Is it exothermic reaction or endothermic reaction?
Answer:
Endothermic reaction.

9. What is the role of a catalyst in a chemical reaction?
Answer:
Substances used to alter the speed of a chemical reaction, are called catalysts. For example, metallic iron is used as a catalyst in the manufacture of ammonia by Haber’s process.

10. Why photosynthesis is a chemical reaction?
Answer:
1. Photosynthesis is a process in which light energy from the sun is used by the plants to prepare starch from carbon dioxide and water.

2. The sunlight uses the chemical reaction between carbon dioxide and water, which finally ends up in the production of starch (photo means light and synthesis means production). These chemical reactions in used by light are called as photochemical reactions.

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