Softening water

• What does hard water contain?

  • Calcium ions Ca^2+
  • Magnesium Mg^2+
• What are the two types of hard water?

  • Permanent hard water and temporary hard water
  • Permanent hard water remains hard when boiled
  • Temporary hard water is softened when boiled
  • Temporary hard water contains hydrogen carbonate ions HCO3-
• What happens to Temporary hard water?

  • When temporary hard water is boiled, the hydrogen carbonate ions decompose to produce carbonate ions CO3^2-. The carbonate ions then react with magnesium or calcium to form precipitates
• Temporary hard water equation

  • Ca(HCO2)2 (aq) --- CaCO3 (s) + H2O (l) +CO2 (g)
• What is the precipitate of calcium carbonate called?

  Limescale
• How can permanent hard water be made soft?

  • By removing the dissolved Calcium and Magnesium ions
  • This can be done by adding washing soda crystals to the water
  • Washing soda contains sodium carbonate. It reacts with the calcium ions and the magnesium ions to form precipitates of magnesium carbonate and calcium carbonate
• Water filters


  • Built to treat hard water
  • They contain ion exchange resins
  • The resin is usually made of a polymer and is in the shape of a bead
  • The beds contain ions such as Sodium and hydrogen because they don't cause hardness
  • When the water passes through the resin, the calcium and magnesium ions that cause water hardness are exchanged for sodium and hydrogen ions which make the water soft
• In conclusion, how is hard water made soft?

  By removing the calcium and magnesium ions