Page 245 - ICSE Chemistry 8

LOGICAL THINKING

1. Jus fy the law of conserva on of mass for the following reac on.

BaCl 2 + Na SO BaSO 4 + 2NaCl
2
4
barium chloride sodium sulphate barium sulphate sodium chloride
2. Why is glowing of an electric bulb on the passage of electric current considered a physical change?

3. Ananya dissolves sugar in water. What will she obtain? What kind of change is this? How can this
process be reversed?

4. It is a chemical change by which bread is made. Name the change. Describe this process. Why is it
also considered slow and desirable change?

5. What kind of a mixture is iron fi lings and sulphur powder? How can this mixture be separated?
6. Garima wants to separate small stones present in pulses. Which method of separa on should she
adopt? What is the principle on which the method is based?
7. It is a separa on technique in which a suitable liquid is mixed with the mixture and compressed air is
allowed to pass through the mixture. Name the separa on technique. What is the principle on which
the technique is based? How is the technique carried out?

8. Ritvik has been asked to separate a mixture of immiscible liquids. Which separa on technique will
he use to separate the mixture? How is the technique carried out?

9. Mahira has been asked to separate a mixture of CaCO and NaCl. Which method(s) should she use
3
to separate the mixture? Describe the process.
10. How is the inward force exerted by the nucleus balanced by the outward force of the moving
electrons in an atom?

11. How will aluminium and magnesium form electroposi ve ions? Discuss.
12. A compound is formed by combining calcium and hydroxide which is a radical. Name the compound
and write its chemical formula.
13. When a solid compound X is heated, oxygen gas is evolved. If a glowing splinter is brought near the
mouth of the test tube, it bursts into fl ame. Name the compound. Write the chemical equa on that
represents the reac on.

14. When a solid compound A is heated, reddish-brown nitrogen gas is evolved with oxygen. Also, a
yellow-coloured compound B is formed. Name the compounds. Write the chemical equa on that
represents the reac on.
15. The reac on between copper oxide and hydrogen to form copper and water is a redox reac on.
Write the chemical equa on to represent the reac on. Name the following.
(a) The substance oxidised
(b) The substance reduced
(c) The oxidising agent
(d) The reducing agent

16. Why is dilute nitric acid not used to prepare hydrogen?
17. Why does the boiling point of water decrease with decrease in pressure?
18. On applying pressure on two ice cubes, they join together to form one big cube. Why does it happen?
What happens on releasing the pressure? What is the phenomenon called?

231