CBSE Class X Science Chapter 3 Metals and Non-metals Questions and Answers

In-Text Questions & Answers

Section 3.1: Physical Properties (Page 40)

1. Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.

Answer:

• (i) Mercury exists as a liquid at room temperature.
• (ii) Sodium (or lithium/potassium) can be easily cut with a knife.
• (iii) Silver (and copper) are the best conductors of heat.
• (iv) Lead (and mercury) are comparatively poor conductors of heat.

2. Explain the meanings of malleable and ductile.

Answer:

• Malleable: The property of metals that allows them to be beaten into thin sheets when struck or hammered.
• Ductile: The ability of metals to be drawn into thin wires.

Figure 3.1: Metals are good conductors of heat.

Figure 3.2: Metals are good conductors of electricity.

Section 3.2: Chemical Properties of Metals (Page 46)

1. Why is sodium kept immersed in kerosene oil?

Answer: Sodium is an extremely reactive metal that reacts vigorously with oxygen in the air and can catch fire if kept in the open. To protect sodium and prevent accidental fires, it is kept immersed in kerosene oil.

2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water

Answer:

(i) Reaction of iron with steam:

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(ii) Reaction of calcium and potassium with water:

Calcium: Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Potassium: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + heat energy

Figure 3.3: Action of steam on a metal.

3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows:

Metal	Iron(II) sulphate	Copper(II) sulphate	Zinc sulphate	Silver nitrate
A	No reaction	Displacement	—	—
B	Displacement	—	No reaction	—
C	No reaction	No reaction	No reaction	Displacement
D	No reaction	No reaction	No reaction	No reaction

Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of Copper(II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

Answer:

• (i) Metal B is the most reactive metal because it is able to displace iron from iron(II) sulphate solution.
• (ii) Since metal B is more reactive than iron, it is also more reactive than copper. Therefore, when B is added to copper(II) sulphate solution, a displacement reaction will occur, and the blue color of copper(II) sulphate solution will fade.
• (iii) The order of decreasing reactivity is: B > A > C > D.

Figure 3.4: Reaction of metals with salt solutions.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.

Answer:
Hydrogen gas (H₂) is produced when dilute hydrochloric acid reacts with a reactive metal.
Chemical reaction of iron with dilute H₂SO₄:
Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)

5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

Answer:
Zinc is more reactive than iron. When zinc is added to an iron(II) sulphate solution, it displaces iron from its solution. As a result, the greenish color of the iron(II) sulphate solution fades and metallic iron gets deposited.
Chemical reaction:
Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

Section 3.3: How Do Metals and Non-Metals React? (Page 49)

1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na₂O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?

Answer:

(i) Electron-dot structures:

• Sodium (Na, Atomic No. 11: 2, 8, 1): Na•
• Oxygen (O, Atomic No. 8: 2, 6): ••O•• (with 6 valence electrons)
• Magnesium (Mg, Atomic No. 12: 2, 8, 2): •Mg•

(ii) Formation by transfer of electrons:

• Formation of Na₂O: Two sodium atoms each lose one electron to a single oxygen atom:
  2 Na• + ••O•• → 2 [Na]⁺ + [ :O: ]^2- → Na₂O
• Formation of MgO: One magnesium atom loses two electrons to an oxygen atom:
  •Mg• + ••O•• → [Mg]²⁺ + [ :O: ]^2- → MgO

(iii) Ions present:

• In Na₂O: Sodium cation (Na⁺) and Oxide anion (O^2-).
• In MgO: Magnesium cation (Mg²⁺) and Oxide anion (O^2-).

Figure 3.5: Formation of sodium chloride.

Figure 3.6: Formation of magnesium chloride.

Figure 3.7: Heating a salt sample on a spatula.

Figure 3.8: Testing the conductivity of a salt solution.

2. Why do ionic compounds have high melting points?

Answer: Ionic compounds have high melting points because a considerable amount of energy is required to break the strong electrostatic inter-ionic forces of attraction between oppositely charged ions.

Section 3.4: Occurrence of Metals (Page 53)

1. Define the following terms.
(i) Mineral
(ii) Ore
(iii) Gangue

Answer:

• (i) Mineral: Elements or compounds that occur naturally in the earth's crust.
• (ii) Ore: Minerals that contain a very high percentage of a particular metal from which the metal can be extracted profitably.
• (iii) Gangue: Ores mined from the earth contaminated with large amounts of impurities such as soil, sand, etc., are called gangue.

Figure 3.9: Activity series and related metallurgy.

Figure 3.10: Steps involved in the extraction of metals from ores.

2. Name two metals which are found in nature in the free state.

Answer: Gold and silver (or platinum) are metals found in nature in the free state.

3. What chemical process is used for obtaining a metal from its oxide?

Answer: The chemical process used for obtaining a metal from its oxide is reduction (e.g., heating with carbon or displacement using a more reactive metal).

Figure 3.11: Thermit process for joining railway tracks.

Figure 3.12: Electrolytic refining of copper.

Section 3.5: Corrosion (Page 55)

Figure 3.13: Investigating the conditions under which iron rusts.

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

Metal	Zinc	Magnesium	Copper
Zinc oxide	—	—	—
Magnesium oxide	—	—	—
Copper oxide	—	—	—

In which cases will you find displacement reactions taking place?

Answer: Based on the reactivity series (Mg > Zn > Cu):

Metal Oxide	Zinc	Magnesium	Copper
Zinc oxide	No reaction	Displacement	No reaction
Magnesium oxide	No reaction	No reaction	No reaction
Copper oxide	Displacement	Displacement	No reaction

Displacement reactions take place in the following cases:

• Zinc oxide heated with Magnesium.
• Copper oxide heated with Zinc.
• Copper oxide heated with Magnesium.

2. Which metals do not corrode easily?

Answer: Unreactive metals at the bottom of the activity series, such as gold and platinum (or silver), do not corrode easily.

3. What are alloys?

Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Chapter End Exercises (Pages 56–57)

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.
Reason: Copper is more reactive than silver and can displace silver from silver nitrate solution.

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.
Reason: Grease and paint are not suitable for an iron frying pan as they wash off or burn on cooking. Galvanisation (coating of zinc) is durable and safe for cooking utensils.

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.
Reason: Calcium reacts with oxygen to form calcium oxide (CaO), an ionic compound with a high melting point that dissolves in water to form calcium hydroxide.

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.
Reason: Zinc is more reactive and can react with acidic materials present in food to form harmful compounds.

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) Testing method:

• Using the hammer: Strike the given sample. If it flattens into a sheet without breaking, it is malleable (a metal). If it breaks into pieces, it is brittle (a non-metal).
• Using battery, bulb, wires, and switch: Connect the battery, bulb, wires, and switch in series with terminals left open. Insert the sample between the open terminals. If the bulb glows, the sample is a good conductor of electricity (a metal); if it does not glow, it is an insulator (a non-metal).

(b) Assessment of usefulness:
These physical tests are generally effective for rapid classification. However, they have exceptions (e.g., graphite is a non-metal that conducts electricity, and sodium is a metal that is soft). Chemical tests provide a more definitive classification.

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

Answer: Metal oxides that react with both acids as well as bases to produce salts and water are known as amphoteric oxides.
Examples: Aluminium oxide (Al₂O₃) and Zinc oxide (ZnO).

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

Answer:

• Metals that displace hydrogen: Zinc (Zn) and Magnesium (Mg) (or Iron/Aluminium).
• Metals that do not displace hydrogen: Copper (Cu) and Silver (Ag) (or Gold).

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

Answer:

• Anode: An impure block/rod of metal M.
• Cathode: A thin strip of pure metal M.
• Electrolyte: A soluble salt solution of metal M (acidified, if needed).

Figure: Collection of gas formed on heating sulphur powder.

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:

(a) Action of gas (Sulphur dioxide, SO₂):

• (i) On dry litmus paper: No effect or change in color.
• (ii) On moist litmus paper: Turns blue litmus paper red, because sulphur dioxide gas dissolves in moisture to form acidic sulphurous acid.

(b) Balanced chemical equations:
S(s) + O₂(g) → SO₂(g)
SO₂(g) + H₂O(l) → H₂SO₃(aq) (Sulphurous acid)

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

Answer:

1. Painting / Greasing / Oiling: Applying paint or oil prevents direct exposure of iron to air and water.
2. Galvanisation: Coating the iron surface with a thin protective layer of zinc.

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

Answer: Non-metals react with oxygen to form acidic oxides (such as SO₂, CO₂) or neutral oxides (such as H₂O, CO).

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.

Answer:

• (a) Platinum, gold, and silver are highly lustrous and extremely unreactive metals that do not corrode easily when exposed to air and moisture.
• (b) Sodium, potassium, and lithium are soft alkali metals that react vigorously with air and moisture and catch fire easily. Storing them under oil prevents contact with air and moisture.
• (c) When aluminium reacts with oxygen, it forms a thin, tough, and non-reactive protective oxide layer (Al₂O₃) on its surface, which prevents further corrosion. It is also a good conductor of heat.
• (d) It is much easier to reduce a metal oxide into metal using carbon or other reducing agents than to reduce sulphide or carbonate ores directly.

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: Tarnished copper vessels develop a green coating of basic copper carbonate due to reaction with moist carbon dioxide in air. Lemon or tamarind juice contains organic acids (like citric acid or tartaric acid). The acid reacts with the basic copper carbonate, dissolving the layer and restoring the shiny copper surface.

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

Answer:

Property	Metals	Non-metals
Nature of Oxides	Form basic oxides (some are amphoteric).	Form acidic or neutral oxides.
Reaction with Water	React with water/steam to evolve hydrogen gas (except noble metals).	Do not react with water.
Reaction with Acids	Displace hydrogen gas from dilute acids.	Do not displace hydrogen gas from dilute acids.
Ion Formation	Form positive cations by losing electrons.	Form negative anions by gaining electrons.

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: The solution used by the man was Aqua regia (a 3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid). Aqua regia is one of the few reagents capable of dissolving gold. When the gold bangles were dipped in it, the outer dull layer dissolved along with some gold, exposing the shiny inner surface but drastically reducing their mass.

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

Answer: Copper does not react with water or steam at all. On the other hand, steel (which contains iron) reacts with steam to form iron oxide and rusts easily when exposed to hot water and air. Therefore, copper is preferred for making hot water tanks.