MEDIUM
8th Kerala Board
IMPORTANT
Earn 100

Take two beakers and fill three-fourth of them with water. Drop a small piece of sodium in one beaker. Notice the formation of a gas by the vigorous reaction between sodium and water. After the reaction, add two drops of phenolphthalein in both the beakers. What do you observe? 
The presence of which substance is indicated by the colour change in the beaker to which sodium was added?

Important Questions on Chemical Changes

EASY
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 2>Q 2
The alkali formed by the reaction of sodium with water is sodium hydroxide. Metals like sodium and potassium react vigorously with water to form hydrogen gas and the corresponding alkali. Write the reactants and products involved in the above reaction. Write down the chemical balanced equation for this reaction.
MEDIUM
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 1

Add 5 mL dilute hydrochloric acid to a piece of magnesium taken in a test tube.

Which is the gas liberated in this reaction?

Touch the bottom of the test tube. What do you feel?

EASY
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 2
Take a few crystals of potassium permanganate in a dry test tube. Heat the test tube. Bring a glowing incense stick to the mouth of the test tube. What do you observe?
MEDIUM
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 3
Take a few crystals of potassium permanganate in a dry test tube. Heat the test tube. Bring a glowing incense stick to the mouth of the test tube. The stick flares up. What could be the reason?
MEDIUM
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 4
Take a few crystals of potassium permanganate in a dry test tube. Heat the test tube. Bring a glowing incense stick to the mouth of the test tube. The stick flares up. Does residue in the test tube have the colour of potassium permanganate?
MEDIUM
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 5
Take a few crystals of potassium permanganate in a dry test tube. Heat the test tube. Bring a glowing incense stick to the mouth of the test tube. The stick flares up. Can this reaction take place without heating?
EASY
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 3>Q 6
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? 
MEDIUM
8th Kerala Board
IMPORTANT
Science for Class 8 - Part 1>Chapter 6 - Chemical Changes>Exercise 4>Q 1
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?