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Extraction of metals — KCSE Chemistry

KCSE Chemistry · 60 practice questions · 4 syllabus objectives · 4 revision lessons

24 easy19 medium17 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Relate the method of extraction of a metal to its position in the reactivity series

Describe the extraction of iron in the blast furnace including the role of coke, limestone and hot air with equations

Describe the extraction of aluminium by electrolysis of molten aluminium oxide and explain why this method is used

Extraction of metals

Revision Notes

Concise lesson notes for Extraction of metals, written to the KCSE Chemistry marking standard. Read the first lesson free below.

Metal Extraction and Reactivity Series

The method of extraction of a metal is primarily determined by its position in the reactivity series. Metals are categorized as:

  • Highly reactive metals (e.g., potassium, sodium): Extracted using electrolysis.
  • Moderately reactive metals (e.g., iron, zinc): Extracted through reduction with carbon or smelting.
  • Less reactive metals (e.g., gold, silver): Typically extracted by panning or chemical methods.

For example, aluminum is a highly reactive metal, so it is extracted using electrolysis of its ore, bauxite. In contrast, iron, which is moderately reactive, is extracted by reduction with carbon in a blast furnace. Understanding these methods helps predict how different metals can be obtained from their ores based on their reactivity.

In summary, the extraction method reflects the metal's reactivity: higher reactivity requires more energy-intensive methods like electrolysis, while lower reactivity allows for simpler methods.

Key points to remember

  • Highly reactive metals use electrolysis for extraction.
  • Moderately reactive metals are reduced with carbon.
  • Less reactive metals are extracted by simpler methods.
  • Position in the reactivity series dictates extraction method.

Worked example

Question: Explain how the method of extraction of iron relates to its position in the reactivity series.

  • Iron is moderately reactive.
  • It is extracted by reduction with carbon in a blast furnace.

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Lesson 2: Extraction of Iron in the Blast Furnace

Objective: Describe the extraction of iron in the blast furnace including the role of coke, limestone and hot air with equations

The extraction of iron from its ore, mainly hematite (Fe2O3), occurs in a blast furnace. Key materials used include:

  • Coke: A carbon-rich material that serves as a fuel and reducing agent.
  • Limestone: Acts as a flux to remove impurities.
  • Hot air: Introduced to facilitate combustion.

Process Overview:

  1. Coke combustion: Hot air is blown into the furnace, igniting coke:

    C + O2 → CO2

    This reaction generates heat, raising the temperature.

  2. Reduction of iron ore: Carbon dioxide reacts with more coke to produce carbon monoxide:

    CO2 + C → 2CO

    Carbon monoxide then reduces iron(III) oxide to iron:

    Fe2O3 + 3CO → 2Fe + 3CO2

  3. Formation of slag: Limestone reacts with impurities (silica) to form slag:

    CaCO3 → CaO + CO2

    CaO + SiO2 → CaSiO3 (slag)

The molten iron sinks to the bottom, while slag floats on top, allowing for easy separation.

  • Coke acts as a reducing agent and fuel in the furnace.
  • Limestone removes impurities by forming slag.
  • Hot air ignites coke, generating necessary heat.
  • Iron is reduced from iron(III) oxide using carbon monoxide.
  • The overall process leads to molten iron and slag.

Describe the role of coke and limestone in the blast furnace.

  • Coke is a fuel and reducing agent, providing heat and carbon for reduction.
  • Limestone acts as a flux, combining with impurities to form slag.
Lesson 3: Electrolysis of Aluminium Oxide

Objective: Describe the extraction of aluminium by electrolysis of molten aluminium oxide and explain why this method is used

The extraction of aluminium is primarily achieved through the electrolysis of molten aluminium oxide (Al₂O₃). This process involves the following steps:

  1. Preparation of Aluminium Oxide: Aluminium oxide is obtained from bauxite ore, which is purified to remove impurities.
  2. Melting: The aluminium oxide is melted at high temperatures (around 1000°C) to form a molten solution.
  3. Electrolysis Process:
    • The molten aluminium oxide is placed in an electrolytic cell, where it serves as the electrolyte.
    • Anode: Carbon electrodes are used as anodes, where oxygen is released and reacts with the carbon to form carbon dioxide.
    • Cathode: Aluminium ions are reduced at the cathode, forming liquid aluminium, which sinks to the bottom of the cell.

This method is preferred because:

  • Purity: Electrolysis produces high-purity aluminium.
  • Efficiency: It allows for the extraction of aluminium from its oxide, which is abundant.
  • Cost-Effectiveness: Although energy-intensive, the process is economically viable due to the high value of aluminium.
  • Aluminium is extracted by electrolysis of molten aluminium oxide.
  • The process involves melting aluminium oxide and using an electrolytic cell.
  • Carbon anodes produce carbon dioxide during the reaction.
  • Liquid aluminium forms at the cathode after reduction of aluminium ions.
  • Electrolysis yields high-purity aluminium efficiently.

Describe the extraction of aluminium by electrolysis.

  • Aluminium oxide is melted and electrolyzed.
  • Carbon anodes release oxygen, forming CO₂.
  • Aluminium ions are reduced at the cathode, producing liquid aluminium.
Lesson 4: Extraction of Metals Overview

Objective: Extraction of metals

The extraction of metals involves obtaining metals from their ores through various methods. The choice of method depends on the reactivity of the metal and the nature of the ore. Common methods include:

  • Smelting: Used for metals like copper and iron. It involves heating the ore with a reducing agent, often carbon, to separate the metal.
  • Electrolysis: Employed for highly reactive metals such as aluminum. This process uses electrical energy to break down the ore into its constituent elements.
  • Cyanide Process: Used for gold extraction from its ore. The ore is treated with a cyanide solution, which dissolves the gold.

Key points to remember:

  • The reactivity series helps determine the extraction method.
  • Less reactive metals can be extracted by reduction with carbon.
  • More reactive metals require electrolysis for extraction.

Understanding these methods is crucial for grasping how metals are sourced and their applications in various industries.

  • Extraction methods depend on metal reactivity and ore type.
  • Smelting involves heating ores with carbon to extract metals.
  • Electrolysis is used for extracting highly reactive metals.
  • Cyanide process is specific for gold extraction.

Explain how iron is extracted from its ore using smelting.

  • Iron ore (hematite) is heated with carbon in a blast furnace.
  • Carbon reduces iron(III) oxide to iron, releasing carbon dioxide.

Sample Questions

Read 3 questions and answers free. Sign up to access all 60 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER3 marks

Define the process of extracting aluminium from its ore using electrolysis, highlighting the role of molten aluminium oxide. (3 marks)

Answer & marking scheme

Part (a) — 3 marks
Electrolysis involves the decomposition of molten aluminium oxide (Al₂O₃) into aluminium and oxygen (1 mk)
Molten aluminium oxide provides ions that are free to move and conduct electricity (1 mk)
The process requires a high temperature to maintain the molten state of aluminium oxide for effective electrolysis (1 mk)
2
easySHORT ANSWER2 marks

State the role of coke in the blast furnace during the extraction of iron. (2 marks)

Answer & marking scheme

Part (a) — 2 marks
Coke acts as a fuel to provide heat for the furnace (1 mk)
Coke reacts with oxygen to produce carbon monoxide, which reduces iron(III) oxide to iron (1 mk)
3
easySHORT ANSWER4 marks

Name two metals that can be extracted by reduction with carbon and state their positions in the reactivity series. (4 marks)

Answer & marking scheme

Part (a) — 2 marks
Iron (1 mk)
Zinc (1 mk)
Part (b) — 2 marks
Iron is below aluminium in the reactivity series (1 mk)
Zinc is also below aluminium but above copper (1 mk)
4

Name two metals that are extracted using the method of electrolysis and explain why this method is necessary for their extraction. (4 marks)

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Frequently asked questions

What does the KCSE Chemistry topic "Extraction of metals" cover?

Extraction of metals covers Relate the method of extraction of a metal to its position in the reactivity series; Describe the extraction of iron in the blast furnace including the role of coke, limestone and hot air with equations; Describe the extraction of aluminium by electrolysis of molten aluminium oxide and explain why this method is used, and more, all aligned to the official KNEC KCSE Chemistry syllabus.

How many practice questions are available for Extraction of metals?

HighMarks has 60 Extraction of metals practice questions for KCSE Chemistry, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Chemistry syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

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