IGCSE Chemistry - Topic 9 Metals Notes

Topic 9 Metals

9.1 Properties of Metals

  • Physical Properties Comparison:

    • Metals vs Non-metals:
    • Thermal Conductivity: Good for metals, poor for non-metals.
    • Electrical Conductivity: Good for metals, poor for non-metals.
    • Malleability: Metals are malleable (can be shaped), while non-metals are usually soft or brittle.
    • Ductility: Metals can be drawn into wires; non-metals generally cannot.
    • Melting/Boiling Points: Metals typically have high melting and boiling points whereas non-metals usually have low.

  • Chemical Properties:

    • Reactions with Dilute Acids: Produce salts and hydrogen gas.
    • Reactions with Cold Water/Steam: Varies with reactivity; can produce hydroxides and hydrogen gas.
    • Reactions with Oxygen: Form basic oxides (e.g., metal + O$_2$ → metal oxide).

9.2 Uses of Metals

  • Aluminium:

    • Aircraft Manufacturing: Low density.
    • Overhead Electrical Cables: Low density and good conductivity.
    • Food Containers: Corrosion resistance.

  • Copper:

    • Electrical Wiring: Excellent conductivity and ductility.

9.3 Alloys and Their Properties

  • Definition: Alloys are mixtures of metals with other elements.

  • Examples:

    • Brass: Copper and zinc; used for decorative items and musical instruments.
    • Stainless Steel: Iron with chromium, nickel; used for cutlery due to hardness and rust resistance.

  • Properties:

    • Alloys are generally harder and stronger than pure metals due to different sized atoms preventing easy slip of atomic layers.

9.4 Reactivity Series

  • Order of Reactivity:

    • Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold.

  • Reactions:

    • Potassium, Sodium, Calcium: React with cold water.
    • Magnesium: Reacts with steam.
    • Metals with Dilute Acids: E.g. Zn + HCl → ZnCl$2$ + H$2$.

  • Aluminium: Apparent unreactivity due to protective oxide layer.

9.5 Corrosion of Metals

  • Rusting:

    • Requires oxygen and water to form hydrated iron(III) oxide (rust).
    • General equation: [ 4Fe + 3O2 + 4H2O \rightarrow 2Fe2O3 ullet 2H_2O ]

  • Prevention Methods:

    • Barrier Methods: Painting, greasing, plastic coating.
    • Sacrificial Protection: Using zinc to protect iron (zinc oxidizes preferentially).

9.6 Extraction of Metals

  • Extraction Methods:

    • Electrolysis: Used for very reactive metals like aluminium (from bauxite).
    • Reduction with Carbon: Used for less reactive metals (e.g., zinc, iron).

  • Iron Extraction:

    • Conducted in a blast furnace from hematite using coke (carbon) and limestone.
    • Key Reactions:
    • [ C + O2 ightarrow CO2 ]
    • [ Fe2O3 + 3CO
      ightarrow 2Fe + 3CO_2 ]

  • Aluminium Extraction:

    • Dissolved in molten cryolite for efficient electrolysis.
    • Reactions at electrodes:
    • Cathode: [ Al^{3+} + 3e^- \rightarrow Al ]
    • Anode: [ 2O^{2-} \rightarrow O_2 + 4e^- ]

Notes on the Reactivity Series and Metals Competition

  1. More reactive metals displace less reactive metals from their compounds.
  2. Example displacements:
    • Iron can displace copper from copper(II) sulfate:
      [ CuSO4 + Fe ightarrow FeSO4 + Cu ]

Practical Applications

  • Sacrificial Protection of Iron: Used in structures exposed to the elements. Zinc sacrifices itself by oxidizing before iron.
  • Galvanizing: Coating iron/steel with zinc to prevent rust.

Summary and Conclusion

  • Properties and reactivity define the uses and methods of extraction of metals.
  • Understanding the reactivity series is crucial for predicting metal reactivity and displacement in reactions, as well as explaining corrosion and protection methods.