SCERT KERALA TEXTBOOKS SOLUTIONS & NOTES: Class 8 Basic Science (English Medium) Chapter 06 Chemical Changes
Textbooks Solution for Class 8th Basic Science (English Medium) | Text Books Solution Basic Science (English Medium) Chapter 06 Chemical Changes
ഈ അദ്ധ്യായം Malayalam Medium ഉടൻ അപ്‌ലോഡ് ചെയ്യും.
SCERT Solutions for Class 8 Basic Science Chapterwise 
Class 8 Chemistry - Questions and Answers 
Chapter: 06 - Chemical Changes 
* The figure shows the arrangement of apparatus for coating silver on an iron bangle
a) Identify 'x'
b) Which type of chemical reaction is this?
c) Which solution should be used if copper is to be coated instead of silver?
d) In which name is this process known?
Ans.
a) Ag
b) Electrochemical reactions
c) CuSO4 Solution
d) Electroplating.

* The cell used in the mobile phone is ------------------------
(Dry cell, Lithium-ion cell, Nickel-cadmium cell, Mercury cell)
Ans. Lithium-ion cell.

* The cell used in the watches and calculators are ------------------------
(Dry cell, Lithium-ion cell, Nickel-cadmium cell, Mercury cell)
Ans. Mercury cell 

* Certain medicines are stored in brown bottles. Why?
Ans. The medicines stored in transparent bottles undergo reaction in presence of light and their quality is lost.

* Match the Following

A

B

a) Reaction between Zn and HCl

Photochemical reaction

b) Silver is plated on Iron bangle

Exothermic reactions

c) Photosynthesis

Endothermic reactions

d) Decomposition of KMnO4

Electrochemical reactions
Ans. 
a) Exothermic reactions
b) Electrochemical reactions
c) Light reactions
d) Endothermic reactions 

* Chemical change is a permanent change but physical change is a temporary change. Justify
Ans.
During a physical change, only a change in the arrangement molecule occurs. It can be easily brought back to its original state. But during chemical change new molecules are formed and hence it cannot be brought back to the original state. So it is permanent. 

* (i) Magnesium + Hydrochloric acid →Magnesium chloride + Hydrogen + Heat
(ii) Potassium permanganate + Heat →Potassium manganate + Manganese dioxide + Oxygen
To which type of thermal reactions do the above reactions belong
Ans.
(i) Exothermic reactions
(ii) Endothermic reactions 

* a) Which is the product obtained by Photosynthesis?
b) In which form is this product stored in the fruits and tubers of plants?
Ans.
a) Glucose
b) Starch

* Leaves are the food factories of nature.
a) Name the process by which leaves produce food
b) Write the reactants of these reactions
c) Which are the products of this reaction?
d) To which category of reactions do this reaction belongs?
Ans.
a) Photosynthesis
b) Water, Carbon dioxide
c) Glucose, oxygen
d) Photochemical reactions 

* Analyse the given chemical reactions and write answers to the questions
(i) Nitrogen + Oxygen + Heat → Nitric oxide
(ii) Calcium oxide + Water → Calcium hydroxide + Heat
a) Write the reactants in each chemical reactions
b) Which of these reactions is exothermic?
Ans.
a) (i) Nitrogen, Oxygen
(ii) Calcium oxide, Water
b) ii 
* The type reactions to which the neutralisation reaction between Sodium hydroxide and Hydrochloric acid belongs to is
(Endothermic, Exothermic, Absorbs light, Emits light)
Ans. Exothermic 

* Complete the table

Chemical change

Main energy change

Name of chemical reactions

Reaction between Mg and HCl

.............(a)...........

.................(b)...............

Glow of firefly

..........(c)............

.................(d)................

Gold plating on copper

...........(e)...........

.................(f)..............
Ans.
a) Heat energy
b) Exothermic reactions
c) Light energy
d) Photochemical reactions
e) Electrical energy
f) Electrochemical reactions

* Arrange the apparatus as in figure and electricity is passed through the circuit.
a) What is the change in colour of copper sulphate solution?
b) What change do you observe on the carbon rods?
c) Which energy form is absorbed here?
Ans.
(a) Colour fades
(b) Red coloured Copper is deposited in the carbon rods
(c) Electrical energy

* An incomplete equation for the reaction of dissociation of Potassium permanganate by absorbing heat energy is given.
Potassium permanganate + Heat →-----X----- + Manganese dioxide + Oxygen
a) Which product is represented by x?
(Potassium chloride, Potassium manganate, Manganese chloride, Sodium hydroxide)
Ans. Potassium manganate

* (i) Magnesium + Hydrochloric acid →Magnesium chloride + Hydrogen + Heat
(ii) Potassium permanganate + Heat →Potassium manganate + Manganese dioxide + Oxygen
To which type of thermal reactions do the above reactions belong
Ans.
(i) Exothermic reactions
(ii) Endothermic reactions

* Chemical change is a permanent change but physical change is a temporary change. Justify
Ans.
During a physical change, only a change in the arrangement molecule occurs. It can be easily brought back to its original state. But during chemical change new molecules are formed and hence it cannot be brought back to the original state. So it is permanent. 

* A few crystals of potassium permanganate are heated in a dry test tube. A glowing incense stick is brought to the mouth of the test tube
a) Write your observation
b) Which gas is formed here?
Ans.
a) The incense stick fares up
b) O₂ 

* The equation of the reaction between magnesium and hydrochloric acid is given
Mg + 2HCl → MgCl₂ + H₂
Which energy is produced along with the products
(Heat, Light, Electricity)
Ans. Heat 

* New products are formed when sodium metal reacts with water
a) Which are the reactants of this reaction?
b) Write the products
c) Write the chemical equation
Ans.
a) Na, H₂O
b) NaOH, H₂
c) 2Na + 2H₂O →2NaOH + H₂ 

* Select the correct statements suitable for chemical changes from the following
* No new substance is formed
* New molecules are formed
* Permanent change
* Temporary change
Ans.
* New molecules are formed
* Permanent change 
* Two beakers are taken in one of the water is taken and in the other same amount of kerosene is taken, add two sodium pieces of the same size to each of them.
a) In which beaker chemical reaction takes place?
b) If we add two drops of phenolphthalein to each beaker in which one colour changes?
c) The presence of which substance is indicated by the colour change
Ans.
a) In the beaker containing water
b) In the beaker containing water
c) NaOH or Alkali 

* Some changes are given in the box. Classify them into physical and chemical changes

* Water changes to water vapour

* Burning of firewood

* Rusting of iron

* Cutting firewood into small pieces

 Ans.

 Physical change

 Chemical change

* Water changes to water vapour

* Cutting firewood into small pieces

* Burning of firewood

* Rusting of iron
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