Class 10 Science Notes Chapter 3 (Chapter 3) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 3, 'Metals and Non-metals', from your NCERT Exemplar book. This is a crucial chapter, not just for your board exams, but also for various government competitive exams where General Science is a component. Pay close attention to the details, especially the exceptions and applications.

Chapter 3: Metals and Non-metals - Detailed Notes

1. Introduction:

• Elements are broadly classified into Metals and Non-metals based on their properties.
• Metals: Elements that tend to lose electrons (electropositive) to form positive ions (cations). Examples: Iron (Fe), Copper (Cu), Gold (Au), Sodium (Na), Calcium (Ca).
• Non-metals: Elements that tend to gain electrons (electronegative) to form negative ions (anions) or share electrons to form covalent bonds. Examples: Carbon (C), Oxygen (O), Sulphur (S), Chlorine (Cl), Hydrogen (H).
• Metalloids: Elements showing properties intermediate between metals and non-metals. Examples: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As).

2. Physical Properties:

3. Chemical Properties of Metals:

• Reaction with Oxygen (Air):

  • Metal + Oxygen → Metal Oxide
  • 4Na(s) + O₂(g) → 2Na₂O(s) (Sodium Oxide)
  • 2Mg(s) + O₂(g) → 2MgO(s) (Magnesium Oxide)
  • 2Cu(s) + O₂(g) → 2CuO(s) (Copper(II) Oxide - black)
  • 4Al(s) + 3O₂(g) → 2Al₂O₃(s) (Aluminium Oxide)
  • Nature of Metal Oxides: Generally basic in nature (turn red litmus blue). Na₂O(s) + H₂O(l) → 2NaOH(aq)
  • Amphoteric Oxides: Some metal oxides (like Al₂O₃, ZnO) show both acidic and basic behaviour. They react with both acids and bases to form salt and water.
    • Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l) (Acting as a base)
    • Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l) (Sodium Aluminate - Acting as an acid)
  • Reactivity: Metals like Na, K react vigorously even at room temp (kept under kerosene). Mg, Al, Zn, Pb form a protective oxide layer preventing further oxidation (passivation). Fe doesn't burn but iron filings burn vigorously. Cu doesn't burn but forms a black CuO layer. Ag, Au do not react with oxygen easily.
  • Anodising: Process of forming a thick oxide layer on Aluminium, making it resistant to corrosion.

• Reaction with Water:

  • Metal + Water → Metal Hydroxide + Hydrogen (if soluble oxide forms hydroxide)
  • Metal + Water → Metal Oxide + Hydrogen (if insoluble oxide)
  • Highly Reactive Metals (Na, K, Ca): React violently with cold water.
    • 2Na(s) + 2H₂O(cold) → 2NaOH(aq) + H₂(g) + Heat (H₂ catches fire)
    • Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g) (Ca starts floating as H₂ bubbles stick)
  • Moderately Reactive Metals (Mg, Al, Zn, Fe):
    • Mg reacts with hot water: Mg(s) + 2H₂O(hot) → Mg(OH)₂(aq) + H₂(g)
    • Al, Zn, Fe react only with steam:
      • 2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)
      • 3Fe(s) + 4H₂O(g) ⇌ Fe₃O₄(s) + 4H₂(g) (Iron(II,III) oxide)
  • Less Reactive Metals (Pb, Cu, Ag, Au): Do not react with water/steam.

• Reaction with Dilute Acids:

  • Metal + Dilute Acid → Salt + Hydrogen Gas
  • Fe(s) + 2HCl(dil) → FeCl₂(aq) + H₂(g)
  • Zn(s) + H₂SO₄(dil) → ZnSO₄(aq) + H₂(g)
  • Mg(s) + 2HCl(dil) → MgCl₂(aq) + H₂(g) (Most vigorous among these)
  • Exception: Metals reacting with Nitric Acid (HNO₃). HNO₃ is a strong oxidizing agent. It oxidizes the H₂ produced to H₂O and itself gets reduced to nitrogen oxides (N₂O, NO, NO₂).
    • Cu(s) + 4HNO₃(conc) → Cu(NO₃)₂(aq) + 2NO₂(g) + 2H₂O(l)
    • However, very dilute HNO₃ reacts with Mg and Mn to evolve H₂ gas.
      • Mg(s) + 2HNO₃(very dil) → Mg(NO₃)₂(aq) + H₂(g)
  • Metals below Hydrogen in the reactivity series (Cu, Hg, Ag, Au) do not displace hydrogen from dilute acids.
  • Aqua Regia: Freshly prepared mixture of concentrated HCl and concentrated HNO₃ in the ratio 3:1. It can dissolve noble metals like Gold (Au) and Platinum (Pt).

• Reaction with Solutions of other Metal Salts (Displacement Reaction):

  • A more reactive metal displaces a less reactive metal from its salt solution.
  • Metal A + Salt Solution of Metal B → Salt Solution of Metal A + Metal B (If A is more reactive than B)
  • Fe(s) + CuSO₄(aq) (Blue) → FeSO₄(aq) (Green) + Cu(s) (Brown deposit)
  • Zn(s) + CuSO₄(aq) → ZnSO₄(aq) (Colourless) + Cu(s)
  • Cu(s) + FeSO₄(aq) → No Reaction (Cu is less reactive than Fe)
  • This forms the basis of the Reactivity Series (Activity Series).

4. Reactivity Series:

• An arrangement of metals in the decreasing order of their reactivity.
  • K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au > Pt
  • (Potassium - Most Reactive) down to (Platinum - Least Reactive)
• Significance: Helps predict displacement reactions, reaction with water/acids, and method of extraction.

5. Chemical Properties of Non-metals:

• Reaction with Oxygen:
  • Non-metal + Oxygen → Non-metal Oxide
  • C(s) + O₂(g) → CO₂(g)
  • S(s) + O₂(g) → SO₂(g)
  • Nature of Non-metal Oxides: Generally acidic or neutral.
    • Acidic Oxides: Dissolve in water to form acids (turn blue litmus red).
      • CO₂(g) + H₂O(l) → H₂CO₃(aq) (Carbonic acid)
      • SO₂(g) + H₂O(l) → H₂SO₃(aq) (Sulphurous acid)
    • Neutral Oxides: Do not show acidic or basic properties (e.g., CO, N₂O, H₂O).
• Reaction with Water: Generally, non-metals do not react with water (though some like Chlorine dissolve slightly).
• Reaction with Dilute Acids: Generally, non-metals do not react with dilute acids to displace hydrogen (as they are electronegative and cannot donate electrons to H⁺ ions).
• Reaction with Salt Solutions: A more reactive non-metal can displace a less reactive non-metal from its salt solution (less common than metal displacement). E.g., Cl₂(g) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq)
• Reaction with Chlorine: Non-metals react with chlorine to form covalent chlorides. H₂(g) + Cl₂(g) → 2HCl(g)
• Reaction with Hydrogen: Non-metals react with hydrogen under specific conditions to form covalent hydrides. N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (Haber's Process)

6. Reaction between Metals and Non-metals: Formation of Ionic Compounds

• Metals lose valence electrons to achieve a stable noble gas configuration (form cations).
• Non-metals gain electrons in their valence shell to achieve a stable noble gas configuration (form anions).
• Metal + Non-metal → Ionic Compound (formed by electron transfer)
• Example: Formation of NaCl
  • Na (2, 8, 1) → Na⁺ (2, 8) + e⁻
  • Cl (2, 8, 7) + e⁻ → Cl⁻ (2, 8, 8)
  • Na⁺ + Cl⁻ → NaCl (Sodium Chloride)
• The electrostatic force of attraction between the oppositely charged ions (cation and anion) holds them together, forming an Ionic Bond or Electrovalent Bond.
• Properties of Ionic Compounds:
  • Usually crystalline solids, hard and brittle.
  • Have high melting and boiling points (due to strong inter-ionic forces).
  • Generally soluble in water but insoluble in organic solvents like kerosene, petrol.
  • Conduct electricity in molten state or aqueous solution (ions are free to move), but not in solid state (ions are fixed).

7. Occurrence and Extraction of Metals (Metallurgy)

• Minerals: Naturally occurring elements or compounds in the Earth's crust.
• Ores: Minerals from which metals can be extracted profitably and conveniently. (All ores are minerals, but not all minerals are ores). Example: Bauxite (Al₂O₃.2H₂O) is the ore of Aluminium.
• Gangue (Matrix): Earthly impurities like sand, soil, rock associated with the ore.
• Metallurgy: The science and technology of extracting metals from their ores and refining them for use.

Steps in Metallurgy:

• Step 1: Concentration (Enrichment) of Ore: Removal of gangue from the ore. Methods depend on physical/chemical property differences between ore and gangue (e.g., Hydraulic washing, Magnetic separation, Froth flotation, Leaching).

• Step 2: Extraction of Metal from Concentrated Ore: Converting the ore into metal. Depends on the metal's position in the reactivity series.

  • (a) Metals Low in Reactivity Series (Ag, Au, Hg, Cu):
    • Often found as free state (Au, Pt) or oxides/sulphides.
    • Oxides can be reduced by heating alone. 2HgO(s) --Heat--> 2Hg(l) + O₂(g)
    • Sulphide ores are first converted to oxides by Roasting (heating strongly in excess air), then reduced.
      • 2HgS(s) (Cinnabar) + 3O₂(g) --Heat--> 2HgO(s) + 2SO₂(g)
      • 2Cu₂S(s) + 3O₂(g) --Heat--> 2Cu₂O(s) + 2SO₂(g)
      • 2Cu₂O(s) + Cu₂S(s) --Heat--> 6Cu(s) + SO₂(g) (Self-reduction/Auto-reduction)
  • (b) Metals in the Middle of Reactivity Series (Zn, Fe, Pb, etc.):
    • Usually present as Sulphides or Carbonates.
    • Convert to Oxides first:
      • Roasting: For sulphide ores. 2ZnS(s) + 3O₂(g) --Heat--> 2ZnO(s) + 2SO₂(g)
      • Calcination: For carbonate ores (heating strongly in limited/no air). ZnCO₃(s) --Heat--> ZnO(s) + CO₂(g)
    • Reduction of Metal Oxide to Metal:
      • Using Carbon (Smelting): ZnO(s) + C(s) --Heat--> Zn(s) + CO(g)
      • Using more reactive metals (Displacement):
        • Thermite Reaction: Reduction using Aluminium powder. Highly exothermic. Used to join railway tracks or cracked machine parts.
          • Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat
          • MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + Heat
  • (c) Metals High in Reactivity Series (K, Na, Ca, Mg, Al):
    • Cannot be reduced by Carbon (high affinity for oxygen).
    • Extracted by Electrolytic Reduction (Electrolysis) of their molten chlorides or oxides.
    • Example: Extraction of Sodium from molten NaCl.
      • At Cathode (Negative electrode): Na⁺(molten) + e⁻ → Na(l) (Metal deposited)
      • At Anode (Positive electrode): 2Cl⁻(molten) → Cl₂(g) + 2e⁻
    • Aluminium is extracted by electrolysis of molten Al₂O₃ dissolved in Cryolite (Na₃AlF₆) and Fluorspar (CaF₂) (to lower melting point and increase conductivity).

• Step 3: Refining (Purification) of Metals: Removal of impurities from the crude metal obtained after reduction.

  • Electrolytic Refining: Most common method. Used for Cu, Zn, Ni, Ag, Au, etc.
    • Anode: Impure metal slab.
    • Cathode: Thin strip of pure metal.
    • Electrolyte: Solution of a salt of the metal being refined (e.g., CuSO₄ solution for copper refining).
    • Process: On passing current, pure metal from the anode dissolves into the electrolyte, and an equivalent amount of pure metal from the electrolyte deposits onto the cathode. Impurities settle below the anode as Anode Mud.
      • At Anode: Cu(impure) → Cu²⁺(aq) + 2e⁻
      • At Cathode: Cu²⁺(aq) + 2e⁻ → Cu(pure)

8. Corrosion:

• The slow eating away of metals by the action of air, moisture, or chemicals (like acids) on their surface.
• Rusting of Iron: Corrosion of iron. Requires both Oxygen and Water (moisture). Rust is hydrated Iron(III) oxide (Fe₂O₃.xH₂O).
  • 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃.xH₂O (Rust)
• Corrosion of Copper: Forms a green coating of basic copper carbonate [CuCO₃.Cu(OH)₂].
• Corrosion of Silver: Forms a black coating of silver sulphide (Ag₂S) by reacting with H₂S in the air.
• Prevention of Corrosion:
  • Painting, Oiling, Greasing (creates a barrier).
  • Galvanization: Coating iron/steel with a layer of Zinc. Zinc is more reactive than iron, so it corrodes preferentially (sacrificial protection).
  • Chrome plating, Tin plating, Anodising.
  • Alloying: Mixing a metal with other metals or non-metals to improve properties and resistance to corrosion.

9. Alloys:

• A homogeneous mixture of two or more metals, or a metal and a non-metal.
• Prepared by melting the primary metal and then dissolving other elements in definite proportions.
• Purpose: To modify properties like hardness, strength, corrosion resistance, melting point, colour etc.
• Examples:
  • Steel: Iron (Fe) + Carbon (C) (small amount) - Hard, strong. Stainless Steel: Fe + Ni + Cr - Corrosion resistant.
  • Brass: Copper (Cu) + Zinc (Zn) - More malleable, stronger than Cu.
  • Bronze: Copper (Cu) + Tin (Sn) - Hard, corrosion resistant, good conductor (used for statues, medals).
  • Solder: Lead (Pb) + Tin (Sn) - Low melting point (used for welding electrical wires).
  • Amalgam: An alloy where one of the metals is Mercury (Hg). Used in dental fillings (with Ag, Sn, Zn).
  • Duralumin: Aluminium (Al) + Copper (Cu) + Magnesium (Mg) + Manganese (Mn) - Light, strong (used in aircraft).
  • Pure Gold (24 carat) is very soft. It is alloyed with Silver (Ag) or Copper (Cu) to make it harder (e.g., 22 carat gold means 22 parts pure gold + 2 parts Ag/Cu).

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 3 for your practice:

1. Which of the following metals exists as a liquid at room temperature?
   (a) Sodium
   (b) Magnesium
   (c) Mercury
   (d) Aluminium

2. Aluminium oxide (Al₂O₃) reacts with both acids and bases. Such oxides are known as:
   (a) Acidic oxides
   (b) Basic oxides
   (c) Neutral oxides
   (d) Amphoteric oxides

3. Which gas is generally produced when a dilute acid reacts with an active metal?
   (a) Oxygen
   (b) Hydrogen
   (c) Carbon dioxide
   (d) Nitrogen dioxide

4. Aqua regia is a mixture of concentrated HCl and concentrated HNO₃ in the ratio:
   (a) 1:3
   (b) 3:1
   (c) 1:1
   (d) 2:1

5. The process of heating a carbonate ore strongly in the absence or limited supply of air to convert it into metal oxide is called:
   (a) Roasting
   (b) Smelting
   (c) Calcination
   (d) Reduction

6. During electrolytic refining of copper, the impure copper acts as the:
   (a) Cathode
   (b) Anode
   (c) Electrolyte
   (d) Anode mud

7. An alloy used for welding electrical wires together has a low melting point. This alloy is:
   (a) Brass
   (b) Bronze
   (c) Solder
   (d) Steel

8. Which of the following pairs will give a displacement reaction?
   (a) FeSO₄ solution and Copper metal
   (b) AgNO₃ solution and Copper metal
   (c) CuSO₄ solution and Silver metal
   (d) NaCl solution and Copper metal

9. Galvanization is a method of protecting iron from rusting by coating it with a thin layer of:
   (a) Tin
   (b) Zinc
   (c) Aluminium
   (d) Copper

10. Which non-metal is essential for combustion and respiration, and forms acidic as well as neutral oxides?
    (a) Sulphur
    (b) Carbon
    (c) Nitrogen
    (d) Oxygen

Answer Key:

1. (c)
2. (d)
3. (b)
4. (b)
5. (c)
6. (b)
7. (c)
8. (b) (Copper is more reactive than Silver)
9. (b)
10. (d) (Oxygen forms acidic oxides like SO₂, CO₂ with non-metals, and neutral oxides like H₂O, CO, N₂O. It is essential for combustion/respiration. Note: Carbon also forms acidic (CO₂) and neutral (CO) oxides but isn't directly essential for respiration itself in the way oxygen is.)

Revise these notes thoroughly. Focus on the reactivity series, the processes involved in metallurgy (roasting, calcination, reduction methods), properties of ionic compounds, corrosion prevention, and composition of common alloys. Understanding the exceptions to general properties is also very important for competitive exams. Good luck with your preparation!