E X E R C I S E S CHAPTER 3 Metals and Non-metals SCIENCE NCERT TEXTBOOK (CBSE) CLASS 10:

 E X E R C I S E S  

CHAPTER  3  Metals and Non-metals 


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

A displacement reaction occurs when a more reactive element displaces a less reactive element from its compound.

  • (a) NaCl solution and copper metal – No displacement reaction because copper is less reactive than sodium.
  • (b) MgCl₂ solution and aluminium metal – This could be a displacement reaction. Aluminium is more reactive than magnesium, so it can displace magnesium.
  • (c) FeSO₄ solution and silver metal – No displacement reaction because silver is less reactive than iron.
  • (d) AgNO₃ solution and copper metal – This is a displacement reaction because copper is more reactive than silver and will displace silver from its compound.

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 – This can provide a protective layer but might not be the most effective.
  • (b) Applying paint – This can help protect the surface from exposure to air and moisture.
  • (c) Applying a coating of zinc – This is galvanization, and it is an excellent method for preventing rusting because zinc is more reactive than iron and corrodes in place of iron.
  • (d) All of the above – All these methods can help reduce rusting, but applying a zinc coating (galvanization) is the most effective.

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 – Calcium oxide (CaO) is a basic oxide that reacts with water to form calcium hydroxide and has a high melting point.
  • (b) Carbon – Carbon dioxide (CO₂) is formed, which is a gas, not a compound with a high melting point.
  • (c) Silicon – Silicon dioxide (SiO₂) has a high melting point and is insoluble in water.
  • (d) Iron – Iron oxide (Fe₂O₃) is formed, but it does not dissolve in water.

Answer: (a) Calcium

4. Food cans are coated with tin and not with zinc because:

  • (a) Zinc is costlier than tin – Not the main reason.
  • (b) Zinc has a higher melting point than tin – Not true; tin has a lower melting point than zinc.
  • (c) Zinc is more reactive than tin – True. Zinc reacts with acids and other substances, making it unsuitable for coating food cans as it could react with the food.
  • (d) Zinc is less reactive than tin – Not true.

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?

  • Connect the battery, wires, and bulb to create a simple circuit. Place the sample material in the circuit and see if the bulb lights up. Metals will conduct electricity and light the bulb, while non-metals will not.

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

  • The test is very useful because metals are good conductors of electricity, while non-metals are generally poor conductors, except for graphite.

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

  • Amphoteric oxides are oxides that can react with both acids and bases to form salts and water.
  • Examples:
    1. Aluminium oxide (Al₂O₃)
    2. Zinc oxide (ZnO)

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

  • Metals that displace hydrogen:

    1. Magnesium (Mg)
    2. Zinc (Zn)

  • Metals that will not displace hydrogen:

    1. Gold (Au)
    2. Platinum (Pt)

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

  • Anode: Impure metal (M) – This will dissolve into the solution as the metal ions.
  • Cathode: Pure metal (M) – This is where the metal ions from the electrolyte will deposit.
  • Electrolyte: A solution containing metal salts of the metal being refined (e.g., for copper refining, copper sulfate solution).

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 the figure below.

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

  • (i) Dry litmus paper? – The gas evolved is sulfur dioxide (SO₂), which is acidic and will turn blue litmus paper red.
  • (ii) Moist litmus paper? – Sulfur dioxide will dissolve in water to form sulfurous acid (H₂SO₃), which is acidic and will turn blue litmus paper red.

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

S(s)+O2(g)→SO2(g)\text{S} (s) + \text{O}_2 (g) \rightarrow \text{SO}_2 (g)

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

  1. Applying a protective coating (e.g., painting or galvanizing with zinc).
  2. Keeping the iron away from moisture and oxygen (e.g., by storing it in a dry place or using oil coatings).

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

  • Non-metals generally form acidic oxides when they combine with oxygen. These oxides react with water to form acids.

Examples:

  • CO₂ (carbon dioxide) forms carbonic acid.
  • SO₂ (sulfur dioxide) forms sulfurous acid.

12. Give reasons:

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

  • Reason: These metals are non-reactive, do not tarnish easily, and have good aesthetic appeal.

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

  • Reason: These metals are highly reactive and react with moisture or air, so they are stored under oil to prevent them from reacting.

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

  • Reason: Aluminium forms a protective oxide layer on its surface that prevents further reaction with air or moisture, making it safe for use in cooking.

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

  • Reason: Oxides are easier to reduce to the metal, which is why ores are converted to oxides during extraction.

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.

  • Lemon and tamarind contain citric acid (or other organic acids), which reacts with the copper oxide (the tarnish) on the surface of the copper. The acids dissolve the copper oxide and restore the shiny appearance of the metal.

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

  • Metals:
    1. React with acids to produce hydrogen gas.
    2. Form basic oxides.
    3. Are good conductors of heat and electricity.
  • Non-metals:
    1. Do not react with acids to produce hydrogen gas (except for some like carbon).
    2. Form acidic oxides.
    3. Are poor conductors of heat and electricity.

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?

  • The solution used by the man was likely aqua regia (a mixture of hydrochloric acid and nitric acid). It can dissolve gold, and the gold would be lost, reducing the weight of the bangles. The gold would dissolve, leaving only a thin layer of the metal, making it look shiny again but much lighter.

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

  • Copper is an excellent conductor of heat, making it ideal for use in hot water tanks. It is also corrosion-resistant, which helps it withstand the exposure to water without rusting.
  • Steel is less corrosion-resistant and would rust over time, especially in hot water, reducing its durability.

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