Study Notes on Metal Extraction and Electrolysis

Electrolysis of Molten Sodium Hydride

  • Electrolysis of molten sodium hydride (NaH) produces hydrogen gas.

  • Electrode A (Positive): Connected to power supply.

  • Electrode B (Negative): Immersed in molten sodium hydride.

  • The heat generated aids the process of electrolysis.

Ion-Electron Equations

  • The following equations take place at the electrodes:

    • At the Anode (Positive Electrode):

    • 2H^{-} -> H_{2} + 2e^{-}

    • At the Cathode (Negative Electrode):

    • 2Na^{+} + 2e^{-} -> 2Na

Key Points:

  • Negative Ions are attracted to the Positive Electrode.

  • To identify which electrode produces hydrogen gas:

    • Based on the equations, hydrogen gas is produced at the anode (Electrode A).

  • The combined balanced redox equation is:

    • 2Na^{+} + 2H^{-} -> 2Na + H_{2}

Extracting Metals from Ores

Overview of Metal Extraction

  • Learning Objective: Understand how metals are extracted from their ores depending on their reactivity.

  • Success Criteria:

    • Define a metal ore as a naturally occurring metal compound.

    • Identify methods used to extract metals based on reactivity.

    • Conduct an experiment to extract metals from ores.

Characteristics of Metals

  • Majority of metals are found in nature as compounds rather than in pure form.

  • Typically, only unreactive metals (e.g., gold and silver) exist uncombined.

    • Metal Ore: A naturally occurring compound of metals.

Examples of Metal Ores

  • Different ores lead to extracting various metals:

    • Aluminium Ore: Bauxite (Aluminium Oxide)

    • Iron Ore: Haematite (Iron(III) Oxide)

    • Tin Ore: Cassiterite (Tin(IV) Oxide)

  • Conclusion: To extract a metal from its ore, it must undergo extraction processes.

  • Initially discovered metals were often the least reactive (e.g., gold and silver).

  • Less reactive metals are easier to extract from their ores.

Methods of Extraction

  • Three primary methods to extract metals from ores:

    1. Heating the Metal Oxide

    2. Heating the Metal Oxide with Carbon

    3. Electrolysis of the Metal Oxide

  • The extraction method employed is based on the metal's reactivity.

Heating Metal Oxides

Objectives

  • Investigate metal extraction from metal oxides through heating methods.

Observations

  • Example Metals:

    • Copper(II) Oxide

    • Silver(I) Oxide

  • Observation: Oxides of metals below copper in the reactivity series decompose upon heating, yielding metals and oxygen.

    • Example: Silver(I) oxide decomposes as follows:

    • 2Ag{2}O(s) -> 4Ag(s) + O{2}(g)

  • This reduction process indicates that silver(I) ions gain electrons during this reaction.

    • Ionic equation representation:

    • 2Ag^{+} + 2O^{2-} -> 4Ag + O_{2}

    • Ag^{+} + e^{-} -> Ag

Heating Metal Oxides with Carbon

Objectives

  • Examine metal extraction through heating metal oxides with carbon.

Observations

  • Example Metals:

    • Copper(II) Oxide

    • Magnesium Oxide

  • Carbon serves as a reducing agent, producing carbon dioxide gas during the reduction of metal oxides.

    • For example:

    • 2CuO + C -> 2Cu + CO_{2}

  • The ionic equations are presented as:

    • Cu^{2+} + O^{2-} + C -> Cu + CO_{2}

    • Cu^{2+} + 2e^{-} -> Cu

Extracting Iron Using the Blast Furnace

Process Overview

  • Iron is extracted from its ore utilizing carbon in a blast furnace.

  • This extraction procedure necessitates substantial heat and occurs in three stages.

Stages of Iron Extraction:

  1. Stage 1: Burn coke (carbon) to create carbon dioxide:

    • C(s) + O{2}(g) -> CO{2}(g)

  2. Stage 2: React carbon dioxide with carbon to yield carbon monoxide:

    • CO_{2}(g) + C(s) -> 2CO(g)

  3. Stage 3: Carbon monoxide reacts with iron(III) oxide in the ore to displace the oxygen, resulting in molten iron:

    • Fe{2}O{3}(s) + 3CO(g) -> 2Fe(l) + 3CO_{2}(g)

Reduction Reaction

  • The iron(III) ion is reduced to iron atoms:

    • Fe^{3+}(aq) + 3e^{-} -> Fe(s)

Electrolysis of More Reactive Metals

Electrolysis Overview

  • More reactive metals (e.g., aluminium, magnesium, calcium, sodium, potassium) must be extracted from their oxides through electrolysis.

  • For example, aluminium extraction can be represented as:

    • Al^{3+}(l) + 3e^{-} -> Al(s)

  • The metal is produced at the negative electrode due to the positive charge of metal ions.

Reactivity Series in Metal Extraction

  • The reactivity series ranks metals by their reactivity:

    • Increasing Reactivity Order:

    1. Potassium

    2. Sodium

    3. Calcium

    4. Magnesium

    5. Aluminium

    6. Zinc

    7. Iron

    8. Copper

    9. Gold (often requires only heat for extraction)

    10. Silver (often requires only heat for extraction)

  • Metals above carbon require electrolysis for extraction.

  • Metals below carbon can be extracted via reduction using carbon, coke, or charcoal.

Experimental Card Sort Activity

  • Sort metal ores according to extraction methods based on reactivity:

    • Reactive Metals:

    • Electrolysis (Calcium Oxide, Sodium Oxide)

    • Less Reactive Metals:

    • Heat alone (Silver Oxide, Gold Oxide)

    • Heat and Carbon (Copper Oxide, Lead Oxide, Tin Oxide, etc.)

Conclusion on Metal Extraction

Learning Intentions

  • Students should now understand how metals are extracted based on their reactivity and methods utilized in such processes.