Solution :: Chapter 3: Metals and Non-metals

 Page No - 40 Questions 

Metals and Non-Metals - Questions and Answers

Page No - 40 Questions

1. Give an example of a metal which:

• (i) is a liquid at room temperature: Mercury (Hg)
• (ii) can be easily cut with a knife: Sodium (Na) (also Potassium (K))
• (iii) is the best conductor of heat: Silver (Ag) (followed by Copper (Cu))
• (iv) is a poor conductor of heat: Lead (Pb) (also Mercury (Hg))

2. Explain the meanings of malleable and ductile.

Malleable: The ability of a metal to be beaten into thin sheets without breaking.
Example: Gold and silver are the most malleable metals.
Ductile: The ability of a metal to be drawn into thin wires.
Example: Gold is the most ductile metal—a 2 km long wire can be drawn from 1 gram of gold.

Page No - 46 Questions

1. Why is sodium kept immersed in kerosene oil?

Sodium is highly reactive and reacts vigorously with oxygen and water in the air, producing heat and hydrogen gas, which can cause fire. To prevent accidental reaction, sodium is stored in kerosene oil, which acts as a barrier against air and moisture.

2. Write equations for the reactions of:

(i) Iron with steam:
3Fe + 4H₂O → Fe₃O₄ + 4H₂
(Iron reacts with steam to form iron(II,III) oxide and hydrogen gas.)
(ii) Calcium and potassium with water:
Calcium with water:
Ca + 2H₂O → Ca(OH)₂ + H₂
(Calcium reacts slowly with cold water to form calcium hydroxide and hydrogen gas.)
Potassium with water:
2K + 2H₂O → 2KOH + H₂ + heat
(Potassium reacts violently with cold water, forming potassium hydroxide and releasing hydrogen gas, which may catch fire.)

3. Samples of four metals A, B, C, and D were tested with different solutions.

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

(i) Which is the most reactive metal?
Metal B is the most reactive because it can displace iron from iron(II) sulfate solution, meaning it is more reactive than iron.
(ii) What would you observe if B is added to a solution of Copper(II) sulphate?
No reaction occurs because B does not displace copper, meaning B is less reactive than copper.
(iii) Arrange the metals A, B, C, and D in the order of decreasing reactivity:
B > A > C > D
B is most reactive (displaces iron from FeSO₄). A is second (displaces copper from CuSO₄). C is third (displaces silver from AgNO₃). D is least reactive (no displacement reactions).

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal?

Hydrogen gas (H₂) is produced.
General equation:
Metal + Dil. HCl → Metal chloride + H₂
Chemical reaction when iron reacts with dilute H₂SO₄:
Fe + H₂SO₄ → FeSO₄ + H₂
(Iron reacts with sulfuric acid to form iron(II) sulfate and hydrogen gas.)

5. What would you observe when zinc is added to a solution of iron(II) sulphate?

Zinc displaces iron from iron(II) sulfate solution because zinc is more reactive than iron.
Observation: The greenish solution of FeSO₄ becomes colorless. A reddish-brown deposit of iron forms on the zinc.
Chemical reaction:
Zn + FeSO₄ → ZnSO₄ + Fe
(Zinc replaces iron from iron(II) sulfate, forming zinc sulfate and iron metal.)

Page No - 49 Questions

1. (i) Electron-Dot Structures for Sodium, Oxygen, and Magnesium

Sodium (Na): ⚫ Na ⚫ (One valence electron)
Oxygen (O): ⚫ O ⚫⚫ (Six valence electrons)
Magnesium (Mg): ⚫ Mg ⚫⚫ (Two valence electrons)

(ii) Formation of Na₂O and MgO by Transfer of Electrons

Formation of Sodium Oxide (Na₂O):
Sodium (Na) has one valence electron and oxygen (O) has six valence electrons. Each Na atom donates one electron to oxygen, which requires two electrons to complete its octet. This forms Na⁺ (sodium ion) and O²⁻ (oxide ion).
Equation:
2Na → 2Na⁺ + 2e⁻
O + 2e⁻ → O²⁻
2Na⁺ + O²⁻ → Na₂O
Formation of Magnesium Oxide (MgO):
Magnesium (Mg) has two valence electrons and oxygen (O) needs two electrons to complete its octet. Mg donates two electrons to oxygen, forming Mg²⁺ (magnesium ion) and O²⁻ (oxide ion).
Equation:
Mg → Mg²⁺ + 2e⁻
O + 2e⁻ → O²⁻
Mg²⁺ + O²⁻ → MgO

(iii) Ions Present in These Compounds

Na₂O (Sodium Oxide): Contains Na⁺ (sodium ion) and O²⁻ (oxide ion).
MgO (Magnesium Oxide): Contains Mg²⁺ (magnesium ion) and O²⁻ (oxide ion).

2. Why Do Ionic Compounds Have High Melting Points?

Strong electrostatic forces exist between oppositely charged ions (cations and anions) in an ionic lattice. A large amount of energy is required to break these strong bonds. This results in high melting and boiling points of ionic compounds. Example: NaCl melts at 1074 K, CaO melts at 2850 K due to strong ionic bonds.

Page No - 53 Questions

1. Define the following terms:

• (i) Mineral: A naturally occurring substance found in the Earth's crust that contains a metal or its compound.
• (ii) Ore: A mineral that contains a high percentage of a particular metal and from which the metal can be extracted profitably.
• (iii) Gangue: The unwanted impurities, such as sand, soil, or rocky material, that are present in an ore.

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

Gold (Au)
Silver (Ag)

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

Reduction is the process used to extract a metal from its oxide. Depending on the metal's reactivity, reduction can be done using:
- Heating alone (for low reactivity metals like mercury and copper).
- Carbon reduction (for moderately reactive metals like iron and zinc).
- Electrolytic reduction (for highly reactive metals like sodium, magnesium, and aluminium).

Page No - 55 Questions

Metallic oxides of zinc, magnesium, and copper heated with different metals:

A displacement reaction occurs if a more reactive metal can displace a less reactive metal from its oxide. The reactivity series helps determine the reactions: Mg > Zn > Cu

Reactions:

• Zinc oxide (ZnO): No reaction with zinc or magnesium (since both are already more reactive than copper).
• Magnesium oxide (MgO): No reaction with zinc or copper (magnesium is the most reactive).
• Copper oxide (CuO):
  • Zinc displaces copper: Zn + CuO → ZnO + Cu
  • Magnesium displaces copper: Mg + CuO → MgO + Cu

Metals that do not corrode easily:

Gold (Au), Platinum (Pt), Silver (Ag) – Found in the free state, highly resistant to corrosion.
Aluminium (Al) – Forms a protective oxide layer, preventing further corrosion.
Stainless Steel (Fe + Cr + Ni) – Rust-resistant due to chromium content.

What are alloys?

Definition: Alloys are homogeneous mixtures of two or more metals, or a metal and a non-metal, designed to enhance properties like strength, corrosion resistance, and durability.

Examples:

• Brass (Cu + Zn): Used in musical instruments and fittings.
• Bronze (Cu + Sn): Corrosion-resistant, used in statues.
• Stainless Steel (Fe + Cr + Ni): Rust-proof, used in utensils and tools.
• Solder (Pb + Sn): Low melting point, used for joining electrical wires.

EXERCISES

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

• (a) NaCl solution and copper metal → No reaction (Copper is less reactive than sodium)
• (b) MgCl₂ solution and aluminium metal → No reaction (Aluminium is less reactive than magnesium)
• (c) FeSO₄ solution and silver metal → No reaction (Silver is less reactive than iron)
• (d) AgNO₃ solution and copper metal → Reaction occurs:
  Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

✅ Correct Answer: (d)

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 (Galvanization)
• (d) All of the above ✅

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 ✅ (Forms CaO, which dissolves in water to form Ca(OH)₂)
• (b) Carbon
• (c) Silicon
• (d) Iron

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 ❌

5. Distinguishing between metals and non-metals using a hammer, battery, bulb, wires, and switch:

• (a) Hammer test: Metals are malleable and can be beaten into sheets, while non-metals break easily.
• (b) Electricity test: Metals conduct electricity, making the bulb glow, while non-metals do not.

(c) These tests are useful because malleability and electrical conductivity are key distinguishing properties of metals and non-metals.

6. Amphoteric oxides:

Definition: Oxides that react with both acids and bases to form salt and water.
Examples: Al₂O₃ (Aluminium oxide), ZnO (Zinc oxide).

7. Metals that displace hydrogen from dilute acids:

Reactive metals: Zinc (Zn), Magnesium (Mg)
Unreactive metals: Copper (Cu), Silver (Ag)

8. Electrolytic refining of metal M:

Anode: Impure metal M
Cathode: Pure metal M
Electrolyte: Aqueous solution of a metal salt (e.g., CuSO₄ for copper refining)

9. Heating sulphur powder:

(a) Action of gas on litmus paper:
(i) Dry litmus paper: No change
(ii) Moist litmus paper: Turns red (due to SO₂ gas forming H₂SO₃ in water)

(b) Balanced equation:
S + O₂ → SO₂

10. Two ways to prevent rusting of iron:

• Galvanization (coating with zinc)
• Painting or oiling

11. Oxides formed when non-metals combine with oxygen:

Acidic oxides: (e.g., CO₂, SO₂, NO₂)

12. Reasons:

• (a) Platinum, gold, and silver are used for jewellery because they are lustrous, non-corrosive, and highly malleable.
• (b) Sodium, potassium, and lithium are stored under oil because they react vigorously with air and water.
• (c) Aluminium is highly reactive but used for cooking utensils because it forms a protective oxide layer (Al₂O₃), preventing corrosion.
• (d) Carbonate and sulphide ores are converted into oxides before extraction because oxides are easier to reduce to metals.

13. Cleaning tarnished copper vessels with lemon or tamarind juice:

Copper forms basic copper carbonate (green layer). Lemon/tamarind contains acid (citric or tartaric acid), which dissolves the carbonate layer, restoring shine.

14. Differences between metals and non-metals (chemical properties):

Property	Metals	Non-metals
Reaction with oxygen	Forms basic oxides (e.g., Na₂O)	Forms acidic oxides (e.g., CO₂)
Reaction with acids	Produces hydrogen gas	No reaction
Conductivity	Good conductors of electricity	Poor conductors
Malleability	Malleable (can be beaten into sheets)	Brittle (breaks when hammered)

15. Detective work – Identifying the solution used by the goldsmith imposter:

The man used aqua regia (a mixture of HCl and HNO₃) to dissolve gold.
The reaction:
Au + HNO₃ + HCl → H[AuCl₄] + NO₂ + H₂O
This removed a layer of gold, making the bangles appear shinier but lighter.

16. Why is copper used for hot water tanks instead of steel?

Copper is a better conductor of heat. Copper is non-corrosive in water, whereas steel can rust over time.