Changes Around Us Book Back Questions 8th Science Lesson 10
8th Science Lesson 10
10] Changes Around Us
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
The head of a matchstick contains potassium chlorate and antimony trisulphide. The sides of the matchbox contain red phosphorous.
Chemical reactions accompanying evolution of heat are called exothermic reactions. Whereas chemical reactions which involve absorption of heat are called endothermic reactions.
The term electrolysis was introduced by Michael Faraday in the 19th century. The word electrolysis is a combination of two terms ‘electron’ and ‘lysis’. Electron is related to electricity and lysis means decomposition.
Limestone is the raw material for quicklime, slaked lime and cement.
The ultraviolet rays from the sun break ozone (O3) molecules in the stratosphere into molecular oxygen and atomic oxygen. This atomic oxygen again combines with molecular oxygen to form Ozone.
Photochemistry is the branch of chemistry which deals with chemical reactions involving light.
Enzymes and yeasts are called biocatalysts.
Choose the best answers:
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) Hydrate 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
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.
State 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.
Match the following:
(a)
1. Rusting – photosynthesis
2. Electrolysis – haber’s process
3. Thermolysis – iron
4. Food – Brine
5. Catalysis – decomposition of limestone
(b)
1. Spoilage – decomposition
2. Ozone – biocatalyst
3. Tarnishing – oxygen
4. Yeast – chemical reaction
5. Calcium oxide – food
Answers:
Choose the best answers:
1. Chemical 2. Light 3. Iron 4. Melanin 5. sodium chloride 6. calcium carbonate 7. Electricity 8. Iron 9. Acid rain 10. CO2
Fill in the blanks:
1.Sunlight 2. Water, Oxygen 3. Ammonia 4. Chlorine and Hydrogen 5. Catalyst 6. Poly phenol Oxidase
State true or false. If false, correct the statement:
1.False
Correct answer: A chemical reaction is a temporary reaction
2.True
3.False
Correct answer: Formation of slaked lime from quicklime is an exothermic reaction
4.True
5.True
Match the following:
a).
1.Rusting- Iron
2.Electrolysis- Brine
3.Thermolysis- Decomposition of limestone
4.Food- Photosynthesis
5.Catalysis- Haber’s process
b).
1.Spoilage – Food
2.Ozone – Oxygen
3.Tarnishing – Chemical reaction
4.Yeast – Biocatalyst
5.Calcium oxide – Decomposition