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Extraction of Metals — CBSE Class 10 Science - Metals and Non-metals

Extracting metals is like solving a puzzle—how do we get a shiny, useful metal from a dull rock? Let’s break down the process and have some fun while learning!

1. Ores and Extraction — The Basics

Key Point:
Metals are not usually found in their pure form. They are found as ores. Ores are naturally occurring rocks that contain enough metal to make it profitable to extract.

Elaboration:

  • Ores often contain unwanted materials called gangue.
  • Extraction means removing the metal from these ores and purifying it.

Examples:

  1. Bauxite is the ore for aluminium.
  2. Haematite is the ore for iron.
  3. Galena is the ore for lead.

Fun Fact: Aluminium was more rare and expensive than gold before people learned to extract it using electricity!

2. Steps of Extraction

Key Point:
Extraction involves three main steps:

a) Concentration of Ore

  • Removes gangue (sand, clay) from the ore.
  • Methods such as gravity separation, froth flotation, or using magnets can be used.

Examples:

  1. Iron ore (magnetic) separated from non-magnetic gangue using a magnet.
  2. Sulphide ores (like zinc blende) separated by froth flotation.

b) Extraction of Crude Metal (Reduction)

  • The concentrated ore is converted to a crude (impure) form of metal.

c) Refining

  • The process of purifying crude metal to obtain the pure, shiny metal we use.

3. Effect of Reactivity Series

Key Point:
The method used to extract a metal depends on its reactivity.

  • Highly Reactive Metals (Top of Reactivity Series): Potassium, Sodium, Calcium, Magnesium, Aluminium.
  • Moderately Reactive Metals (Middle): Zinc, Iron, Lead, Copper.
  • Least Reactive Metals (Bottom): Silver, Gold, Platinum, Mercury.

Examples:

  1. Potassium is extracted using electrolysis because it is very reactive.
  2. Iron is extracted using reduction with carbon because it is less reactive.
  3. Gold is found as nuggets in the ground because it is very unreactive.

4. Extraction Methods for Different Reactivity

a) Highly Reactive Metals — Using Electrolysis

Key Point:
Metals like sodium (Na) and aluminium (Al) are so reactive, they can't be extracted by heating with carbon. They are obtained by electrolysis of their molten compounds.

Detailed Process:

  • Electricity passes through the molten ore.
  • Metal ions move to the cathode and are deposited as pure metal.
  • Non-metal ions go to the anode and are released.

Examples:

  1. Sodium from Sodium Chloride (NaCl):

    • At Cathode: Na⁺ + e⁻ → Na
    • At Anode: Cl⁻ – e⁻ → Cl (forms chlorine gas)

  2. Aluminium from Alumina (Al₂O₃):

    • At Cathode: Al³⁺ + 3e⁻ → Al
    • At Anode: O²⁻ → O₂ + 2e⁻

Fun Connection: Electrolysis is like a video game where electricity helps you unlock a hidden character (metal).

b) Moderately Reactive Metals — Roasting, Calcination, and Reduction

Key Point:
Metals like zinc (Zn) and iron (Fe) are obtained by first converting their ores into oxides (by roasting/calcination), and then reducing these oxides with carbon.

Detailed Process:

  • Roasting: Heating sulphide ores in the presence of air. Converts sulphides to oxides.
    • ZnS + O₂ → ZnO + SO₂
  • Calcination: Heating carbonate ores in absence of air.
    • ZnCO₃ → ZnO + CO₂
  • Reduction: Carbon (as coke/charcoal) takes away the oxygen, leaving the metal.
    • ZnO + C → Zn + CO

Examples:

  1. Copper: CuO + C → Cu + CO
  2. Iron (Blast Furnace): Fe₂O₃ + 3C → 2Fe + 3CO

Fun Analogy: The carbon is like a superhero who fights the evil oxygen and frees the captive metal!

c) Least Reactive Metals — Found Native or by Simple Heating

Key Point:
Metals like gold and silver, and even mercury, are so unreactive that they are found as free metals or can be easily extracted by heating their ores.

Examples:

  1. Mercury(II) oxide heated:
    2HgO → 2Hg + O₂

  2. Silver oxide heated:
    2Ag₂O → 4Ag + O₂

  3. Gold and platinum are found in pure form in nature.

Fun Fact: Some people have found gold nuggets in rivers without any machines!

5. Activity: Extraction of Copper from Copper(II) oxide

Step-by-Step Activity

Materials Needed:

  • Copper(II) oxide powder (CuO)
  • Carbon powder (charcoal)
  • Test tube, spatula, Bunsen burner, tongs

Instructions:

  1. Mix a small amount of CuO and carbon powder in a test tube.
  2. Hold the test tube with tongs and heat it strongly over a Bunsen burner.
  3. Once the reaction is finished, let it cool and sprinkle out the contents on a white tile.
  4. Observe the changes.

Observations:

  • A reddish-brown residue is seen. This is copper metal.
  • Black CuO reacts with carbon to give reddish copper and colorless CO gas.

Equation:
CuO + C → Cu + CO

Key Point Highlighted:
This activity shows that moderately reactive metals (like copper) can be extracted from their oxides by heating with carbon, providing a simple real-life demonstration!

Example:
You can repeat this with iron(III) oxide and get iron using carbon as well.

Scenario-Based Questions

Scenario 1: You are given a lump of iron ore, haematite, and some coke (carbon).

  • Question: How would you extract pure iron from this ore?
  • Answer: By reducing haematite (Fe₂O₃) with coke in a blast furnace:
    Fe₂O₃ + 3C → 2Fe + 3CO.

Scenario 2: Your friend finds some shiny yellow metal in river sand and thinks it is a compound of gold.

  • Question: Is she correct? Why or why not?
  • Answer: She is probably looking at native (pure) gold, as gold is often found in nature in its elemental form due to its low reactivity.

Scenario 3: You have sodium chloride crystals but want to obtain sodium metal.

  • Question: How will you extract sodium from sodium chloride?
  • Answer: By carrying out the electrolysis of molten sodium chloride; sodium is deposited at the cathode.

Scenario 4: A zinc ore is heated in air and produces zinc oxide and a gas that turns limewater milky.

  • Question: What process is this, and what gas is produced?
  • Answer: This is calcination of zinc carbonate. Carbon dioxide (CO₂) is released, which turns limewater milky.

Scenario 5: Your teacher asks why we do not extract aluminium using carbon like we do for iron.

  • Question: What would you answer?
  • Answer: Aluminium is more reactive than carbon, so carbon cannot reduce its oxide. That is why we extract aluminium by electrolysis of its molten oxide (alumina).

Note: Remember, understanding why we choose a certain method (and not just memorizing reactions) will make you a science champion!

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