Reactions of Metals and Non-metals with Oxygen

Oxygen

  • Most abundant element on earth
  • Essential for life
  • Colourless and odourless gas at normal temperature and pressure
  • Highly reactive
    • Spontaneous reactions – no energy required
    • Non-spontaneous reactions – requires activation energy
  • All reactions with oxygen releases energy (heat and light)

Combustion

  • Burning in the presence of oxygen
  • Reaction with oxygen
  • Oxygen atoms react readily with atoms of other elements
  • Product formed is –oxide
  • Substance that burns undergoes chemical change
    • During chemical reaction, energy is released in the form of light and heat energy

Reactions of Metal with Oxygen

  • Product is metal oxide
  • Characteristics:
    • Metal oxides are solids
    • Metal oxides are basic 🡪 form alkaline solutions with water

Reaction of magnesium with oxygen

  • Magnesium + oxygen 🡺 magnesium oxide
  • 2Mg + O2 🡺 2MgO
  • Fast reaction
  • Blinding white light (energy released)

Reaction of iron with oxygen

  • Iron + oxygen 🡺iron oxide
  • 3 Fe + 2O2 🡺 Fe3O4
  • Product – magnetic iron oxide - magnetite

Rust

  • Corrosion = chemical attack on surface of metal which results in wear and breakdown.
  • Rust is a type of corrosion of iron
  • 🡺iron reacts with oxygen in presence of moisture – slow chemical reaction that takes place.
  • Rust is an orange-brown solid
  • Iron oxide (Fe2O3)
  • Occurs faster due to presence of salt or acid rain.
  • Flakes formed and shed, weakens metal (becomes brittle).

Preventing rust

  • Rust is irreversible.
  • Best way is to protect against rust formation– exclusion of oxygen.
  • Cover surface – if layers is compromised another must be added to maintain efficacy.
    1. Paint – easiest and cheapest, less efficient
    2. Oil or lubricant (grease) – water repellent layer coated onto moving parts, must be reapplied from time to time
    3. Electroplating – thin layer of metal (chrome or zinc) added to surface of metal by electrolysis, ex. taps and door handles
    4. Galvanising – iron covered with thin layer of zinc, ex. fencing and water pipes

Reactions of Non-Metals With Oxygen

  • Non-metal + oxygen 🡺 non-metal oxide
  • Characteristics:
    • Non-metal oxides usually gases
    • Non-metal oxides dissolved in water – acidic solutions

Reaction of carbon and oxygen

  • C + O2 🡺 CO2
  • Bright yellow flame
  • Dissolves in water and makes it milky

Reaction of sulfur and oxygen

  • S + O2 🡺 SO2
  • Bright blue flame
  • Sulfur dioxide is a colourless gas with sharp, choking odour

Acid rain

  • Fossil fuels contain carbon and sulfur.
  • When burned carbon dioxide and sulfur dioxide is released into atmosphere
  • Both are non-metal oxides and forms acidic solutions in water
  • Hence – acid rain
  • Detrimental to plants and animals
  • Damages buildings