EASY
8th Kerala Board
IMPORTANT
Earn 100

Add hydrochloric acid to a concentrated solution of sodium hydroxide taken in a test tube. As the reaction proceeds, does the test tube become hot or cold? 

Important Questions on Chemical Changes

MEDIUM
8th Kerala Board
IMPORTANT
Take some silver bromide in two dry watch glasses. Wrap one of them with a black paper. Keep both of them in sunlight for some time.
  • What do you observe?
  • In which watch glass does the colour of silver bromide change? 
  • Which form of energy was responsible for this chemical change? 
MEDIUM
8th Kerala Board
IMPORTANT
What could be the reason for storing certain medicines and chemicals in brown bottles? Think of it. 
MEDIUM
8th Kerala Board
IMPORTANT

Question Image

Set up the apparatus. What changes do you observe when electricity is passed through the circuit? 
• In the colour of copper sulphate solution: 
• On the carbon rods.
• Does it happen if a carbon rod is simply kept in copper sulphate solution? Which form of energy was responsible for this chemical change? Was the energy liberated or absorbed?

HARD
8th Kerala Board
IMPORTANT
Cell Instrument in which it is used
Dry cell Radios
Cameras
Clocks
Toys
Mercury cell Watches
Calculator
Electronic instruments
Nickel- cadmium cell Rechargeable torches 
Cameras
Lithium ion cell Mobile phone
Laptops
  • What do we do with these types of cells after their use?
  • Which among these cells can be recharged and reused? 
  • Do they cause environmental pollution? 
MEDIUM
8th Kerala Board
IMPORTANT

Assess the chemical reactions given below and answer the questions.

Calcium carbonate + heat  Calcium oxide + Carbon dioxide 

Calcium oxide + water Calcium hydroxide + heat 

a) Mention the reactants and products in each case. 

b) Which among these are endothermic? Which one is exothermic? 

EASY
8th Kerala Board
IMPORTANT
Identify the energy change involved and write down what type of chemical reaction takes place in burning of a candle.
EASY
8th Kerala Board
IMPORTANT
Identify the energy change involved and write down what type of chemical reaction takes place in glowing of a fire fly.
MEDIUM
8th Kerala Board
IMPORTANT
Identify the energy change involved and write down what type of chemical reaction takes place in plating a copper ring with gold.