C9: Metals

  1. Properties of metals

  • Metal + dilute acid → salt + hydrogen

  • metal + water (steam) → metal oxide + hydrogen

  • metal + (cold) water → metal hydroxide + hydrogen

  1. Uses of metals

  • Aluminum in the manufacture of aircraft:

    • high strength-to-weight ratio

    • low density

    • resists corrosion

  • aluminum in overhead cables

    • good electrical conductivity

    • low density

    • ductile

  • aluminum in food containers:

    • corrosion resistant from acidic foods

    • non-toxic

  • copper in electrical wiring

    • good electrical conductivity

    • ductile

  1. Alloys and their properties

  • alloys: mixtures of metal with other elements

    • E.g: brass - copper + zinc

      • stainless steel - iron + other elements (chormium, nickel & carbon)

    • Alloys can be harder, stronger & more useful than pure metal

    • uses:

      • Stainless steel: cutlery due to its hardness & resistance to rusting

  1. Reactivity series

  • metals that lose electrons more readily to form cations → more reactive

  • displacement reaction: more reactive metals lose their electrons more easily

  1. Corrosion of metals

  • corrosion: metals react with substances in their environment and are gradually destroyed

  • conditions for rusting: presence of oxygen & water

    • only happens on the surface

  • Barriers method:

    • painting, greasing & coating in plastic: prevents oxygen & water to come in contact with the metal

    • galvanizing steel: coating steel/iron with a thin layer of zinc as protection

      • sacrificial protection

      • if coating gets scratched → coating corrodes instead of iron/steel

    • sacrificial protection: placing a more reactive metal on the metal you want to protect

      • water + oxygen reacts with sacrificial metal first (more reactive)

      • works by electron donation:

        • oxygen + metal → cation

        • more reactive metals lose electrons more easily

        • reacts with oxygen first

      • needs to be replaced continuosly

  1. Extraction of metals

  • more reactive metals are found in minerals as compunds called ors

    • high tendency to lose their electrons & form cations

  • Extraction of iron:

    • hematite: ore containing iron oxide Fe2O3

      • iron is extracted from hematite by reduction of iron oxide in the blast furnace

    • raw materials:

      • hematite

      • coke (carbon): fuel and reducing agent

      • limestone (CaCO3): removes impurities as slag

      • hot air: supplies oxygen for combustion

    • Fe2O3 dissolves in molten cryolite to reduce melting point

    • metals higher up in reactivity series are harder to extract from ore due to its stronger bond with its oxide

  • Extraction of aluminum:

    • bauxite

    • extracted by electrolysis

      → aluminum is higher in the reactivity series than carbon (cannot be extracted by the reduction of carbon )