Lesson:Metals and Non-metals

Question 1

Which of the following pairs will give displacement reactions?

(a) $N a C l$ solution and copper metal

(b) $M g C l_{2}$ solution and aluminium metal

(d) $A g N O_{3}$ solution and copper metal.

Solution:

(d)

Question 2

Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease

(b) Applying paint

(d) All of the above.

Solution:

(c)

Question 3

An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

(a) Calcium

(b) Carbon

(d) Iron.

Solution:

(a)

Question 4

Food cans are coated with tin and not with zinc because

(a) Zinc is costlier than tin.

(b) Zinc has a higher melting point than tin.

(d) Zinc is less reactive than tin.

Solution:

(c)

Question 5

You are given a hammer, a battery, a bulb, wires and a switch.

(a) How could you use them to distinguish between samples of metals and non-metals?

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.

Solution:

(a) If the given sample can be beaten into thin sheets by the hammer, then it is a metal, otherwise it is a non-metal.

Similarly, if a circuit made by the given sample, the battery, the bulb, the wires and the switch conducts electricity, then it is a metal. Otherwise the sample is a non-metal.

(b) The above tests are useful as they help in distinguishing between metals and non-metals without involving any chemical reaction.

Question 6

What are amphoteric oxides? Give two examples of amphoteric oxides.

Solution:

The oxides which behave both as acidic as well as basic in nature are called amphoteric oxides.

Examples: aluminium oxide ( $A l_{2} O_{3}$ ), zinc oxide ( $Z n O$ )

Question 7

Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Solution:

Sodium and aluminium will displace hydrogen from dilute acids.

Mercury and copper cannot 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?

Solution:

In the electrolytic refining of a metal M:

· The anode is the impure metal M

· The cathode is the thin strip of pure metal M

· The electrolyte is the solution of the salt of the metal M

Question 9

Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on?

(i) Dry litmus paper?

(ii) Moist litmus paper?

(b) Write a balanced chemical equation for the reaction taking place.

Solution:

(a) (i) There will be no action on the dry litmus paper.

(ii) The colour of the moist litmus paper turns red as sulphur is a non-metal and the oxides of non-metals are acidic in nature.

(b) $S (s) + O_{2} (g) \to S O_{2} (g)$

Question 10

State two ways to prevent the rusting of iron.

Solution:

Two ways to prevent the rusting of iron are:

(i) Application of oil or paint

(ii) Galvanisation

Question 11

What types of oxides are formed when non-metals combine with oxygen?

Solution:

Neutral or acidic oxides are formed when non-metals combine with oxygen. Examples are $N O_{2}$ and $S O_{2}$ are neutral oxides.

Question 12

Give reasons:

a) Platinum, gold and silver are used to make jewellery.

b) Sodium, potassium and lithium are stored under oil.

c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Solution:

(a) Platinum, gold and silver are used to make jewellery because they are very lustrous, less reactive and do not corrode easily.

(b) Sodium, potassium and lithium, being highly reactive, are stored under oil to prevent their reaction with air and moisture.

(c) Aluminium is light in weight and is a good conductor of heat. It reacts with oxygen present in the air to form a thin layer of aluminium oxide. This oxide layer is very stable. It prevents further reaction of aluminium with oxygen.

So, even though aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction. This is due to the fact that metals can be more easily extracted from their oxides rather than from their carbonates and sulphides.

Question 13

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Solution:

Copper reacts with carbon dioxide in the air to form copper carbonate. Due to this, it loses its shiny brown surface and a green coating of copper carbonate is formed. The citric acid present in the lemon or tamarind neutralises the copper carbonate, thereby dissolving the layer and thus helping in cleaning the vessel.

Question 14

Differentiate between metal and non-metal on the basis of their chemical properties.

Solution:

Metals	Non-metals
Metals form basic oxides on reaction with oxygen.	Non-metals form acidic oxides or neutral oxides on reaction with oxygen.
Some metals displace hydrogen from water.	Non-metals do not react with water to evolve hydrogen.
Metals usually displace hydrogen from dilute acids.	Non-metals do not react with dilute acids.

Question 15

A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Solution:

The solution he had used was Aqua regia. It is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. When a gold ornament is cleaned with Aqua regia, some of the gold gets dissolved in it. This results in the loss in weight of the gold ornament.

Question 16

Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Solution:

Copper does not react with any form of water, be it cold, hot or steam. On the other hand, steel (an alloy of iron) reacts with steam to form iron oxide. Due to this reason, copper is used to make hot water tanks, and not steel.