Hard Water

Hard Water

1. Hard water makes Scum and Scale

   • Won't easily form lather with soap - get nasty scum instead
     • 'Hardness minerals' in the hard water reacting with the soap
       • Forms furring or scale - mostly calcium carbonate - on the inside of pipes, boilers and kettles
         • Reduce efficiency so will need to be replaced - expensive - can also block pipes
           • Scale is a thermal insulator - kettle with scale on the heating element takes longer to heat up - less efficient

2. Hardness is caused by Ca2+ and Mg2+ ions

   • Most hard water is hard because it contains a lot of calcium and magnesium ions
     • Hard water in different areas due to the type of rocks - limestone, chalk and gypsum
       • Rain falling on some types of rocks can dissolve magnesium sulfate(soluble) and calcium sulfate(slightly soluble)
   • Other calcium and magnesium salts come from a reaction
     • When CO2 from the air dissolves in rainwater you get carbonic acid (CO2 + H2O=H2CO3) so rainwater is slightly acidic
       • If theres calcium carbonate (CaCO3) in the rocks, calcium hydrogen carbonate is formed (H2CO3 + CaCO3 = Ca(HCO3)2) which is soluble - similar with rocks containing MgCO3

3. Hard Water isn't all bad

   • Ca2+ ions are good for healthy teeth and bones
   • Scale inside pipes forms a protective coating - stops poisonous metal ions getting into drinking water and prevents iron pipes from rust

4. Remove hardness by removing dissolved Ca2+ and Mg2+ ions

   • 1 - By adding sodium carbonate
     • The carbonate ions join onto the calcium or magnesium ions and make an insoluble precipitate
       • eg. Ca2+(aq) + CO32-(aq) = CaCO3(s)
   • 2 - By ion exchange columns
     • Sometimes a water supply is fed through an ion exchange column to remove the hardness. These have lots of sodium(or hydrogen) ions and exchange them for calcium or magnesium ions in the water that runs through them
       • eg. Na2Resin(s) + Ca2+(aq) = CaResin(s)+"Na+(aq)
   • 3 - Scale is mainly just calcium carbonate and can be dissolved by acid - descaling products