NCERT Solutions for Class 10 Science Chapter 3 Metals and Non-metals

1. Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl2 solution and aluminium metal

(c) FeSO4 solution and silver metal

(d) AgNO3 solution and copper metal.

Answer: (d) AgNO3 solution and copper metal.

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

(a) Applying grease

(b) Applying paint

(c) Applying a coating of zinc

(d) All of the above.

Answer: (c) Applying a coating of zinc

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 (c) silicon (d) iron.

Answer: (a) calcium

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.

(c) zinc is more reactive than tin.

(d) zinc is less reactive than tin.

Answer: (c) zinc is more reactive than tin.

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.

Answer:

a) Metals have shiny appearance, whereas, non metals look dull. Metals cans be beaten into sheets, whereas, non metals breaks if beaten. Metals produce sound, while non metals don’t. If these samples are connected in circuit, then metals will conduct electricity and nonmetals will not.

b) Above test is distinguishes between metals and nonmetals based on their physical properties.

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

Answer: Oxides which behaves as acidic as well as basic oxides is known as amphoteric oxides. Examples of amphoteric oxides are zinc oxide or ZnO, aluminium oxide Al2O3, lead oxide PbO, etc.

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

Answer: Zinc, sodium, magnesium,etc are metals that displaces hydrogen from dilute acids. Copper, silver, gold, etc are the metals that do not displace hydrogen from dilute acids.

8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Answer: Anode will be impure metal M, cathode will be strip made of pure metal M, and electrolyte will be salt solution of metal M.

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.

Answer: Dry litmus paper remains unaffected. When moist litmus paper comes in contact with sulphur dioxide reacts with moisture, thereby forming sulfurous acid. Following is balanced chemical equation of the reaction –

S + O₂ ⟶ SO₂

                        (Sulphur Dioxide)

SO₂ + H₂O ⟶ H₂SO₃

                               (Sulfurous Acid)

10. State two ways to prevent the rusting of iron.

Answer: 1) Painting – Applying paint on the surface of iron material breaks the contact of air and moisture thus prevent it from rusting.

2) Galvanisation – Iron material is coated with zinc by the method of galvanization which prevents it from air and moisture, thereby, preventing it from rusting.

11. What type of oxides are formed when non-metals combine with oxygen?

Answer: Non metal combines with oxygen to form acidic oxides.

Examples of such oxides are – SO₂ , N₂O₃, N₂O₅, etc.

12. Give reasons

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

Answer: These metals are used to make jewellery because these are lustrous and do not reacts with other metals easily. Also, these metals do not undergo corrosion.

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

Answer: Sodium potassium and lithium are highly reactive element, when these come in contact with air and water a vigorous reaction takes place. Thus, to prevent their contact with air and water these are kept immersed in oil.

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

Answer: Aluminium being reactive still is resistant to corrosion. When aluminium utensil comes in contact with air, aluminium reacts with air forming a layer of aluminium oxide. Aluminium oxide being stable, do not reacts with air or moisture, thereby preventing further oxidation of aluminium. Also, aluminium is good conductor of heat.

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

Answer: This is because, it is easy to extract metal from their oxides rather than carbonates and sulphide.

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.

Answer: Copper forms copper carbonate and greenish layer appears on the shiny surface of copper vessels. Copper carbonate is basic in nature. However, lemon or tamarind juice is acidic in nature. These neutralises copper carbonate removing the greenish layer from the vessel.

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

Answer :

Metals	Non metals
Metals are electropositive in nature	Non metals are electronegative in nature
Metals are good reducing agent	Non metals are good oxidizing agent
Metals reacts with oxygen to form basic oxide	Nonmetals reacts with oxygen to form acidic or neutral oxide
Reacts with water to form oxides and hydroxides. Some of them reacts with cold water, some with hot or with steam.	Donot reacts with water.

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?

Answer: Ornament must have dipped in the solution called aqua regia which is mixture of hydrochloric acid and nitric acid in 3:1 proportion. When gold ornament is dipped in this mixture it dissolves the outer layer of the gold and shiny inner layer appears. This causes loss of weight of gold jewellery.

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

Answer: Copper doesn’t reacts with water (cold, hot or steam). However, iron is highly reactive with steam. If steel which is made of iron is used to make hot water tanks then it with react with steam generated in hot water tanks. Thus, copper is used instead of steel.

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