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.
What will be the action of gas on
Write a balanced chemical equation for the reaction taking place.
Answer: S + O2 ⇨ SO2
Question 10: State two ways to prevent the rusting of iron.
Answer: Two ways to prevent the rusting of iron are as follows:
Question 11: What type of oxides are formed when non-metals combine with oxygen?
Answer: The non-metallic oxides are acidic in nature.
Question 12: Give reasons
(a) Platinum, gold and silver are used to make jewellery. Why?
Answer: Platinum, gold and silver are at the bottom of the reactivity series. So, they don't react with atmospheric gases. So, they are able to maintain their shine for a long time. Moreover, these are highly ductile and malleable. So, intricate designs can be easily made on items of gold or platinum, making them suitable for ornaments. Hence, these metals are used to make jewelry.
(b) Sodium, potassium and lithium are stored under oil. Why?
Answer: Sodium, potassium and lithium are at the top of the reactivity series. They can easily react with water and even with atmospheric moisture. Their reaction with water is highly exothermic and results in fire. You have read in this chapter about what happens when a small grain of sodium is kept in water. Reaction begins quickly and the reaction mixture catches fire. These metals are stored under oil to prevent their reaction from water and to prevent accidental fire.
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