Question -6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer: Some oxides show both acidic and basic characters. Such oxides are called amphoteric oxides. Amphoteric oxide reacts with acid as well as with base to form salt.
Aluminium oxide and zinc oxide are examples of amphoteric oxide.
When aluminium oxide reacts with a base, it gives salt and water.
When aluminium oxide reacts with an acid it gives salt and water.
Question -7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer: Sodium and zinc can displace hydrogen from dilute acids. On the other hand, copper and silver do not displace hydrogen from dilute acids.
Question -8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer: A rod of impure metal M would be used as anode and a thin strip of pure metal M would be used as cathode. A water soluble salt of metal M would be used as electrolyte.
Question -9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it.
(a) What will be the action of gas on
(i) dry litmus paper?
Answer: There will be no action on dry litmus paper.
(ii) moist litmus paper?
Answer: Since the gas is an oxide of a non-metal hence it will turn moist blue litmus paper to red.
(b) Write a balanced chemical equation for the reaction taking place.
Question -10. State two ways to prevent the rusting of iron.
Answer: Two ways to prevent the rusting of iron are as follows:
(a) By galvanization
(b) By applying a layer of paint
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