Chemistry 3A: Water

Chemistry 3A: Water

1. Hard Water

   • Reacts with soap to form scum.
   • More soap needed to form lather.
   • Caused by calcium and magnesium ions - dissolved when water comes into contact with rocks.
     • Calcium good for development of bones and teeth and reduces risk of heart disease.
     • Soft Water
       • Forms a lather with soap.
       • Less calcium and magnesium ions.
   • Increases cost - more soap is needed; produces scale when heated - reduces effiency of kettles.
     • Blocks pipes + is a thermal insulator - kettle takes longer to boil.
   • Soapless detergents don't form scum.

2. Softening Hard Water

   • Temporary hard water is softened by boiling.
     • Permanent hard water remains hard when boiled.
   • Temp hard water: contains hydrogencarbonate ions, decomposes on heating to produce calcium carbonate (limescale).
   • Perm hard water: add sodium carbonate (washing soda), reacts with Ca and Mg to form an insoluble precipitate - Ca and Mg ions are no longer dissolved, can't make it hard.
   • Ion exchange columns: columns contain, ion exchange resin with sodium (or H) ions on which are exchanged for the Ca and Mg as water runs by.

3. Water Quality

   • Water treatment
     • Mesh screen removes big bits; chemicals added so solids and microbes stick together, fall to bottom; filtration to remove all solids; chlorine added to remove microbes.
     • Water filters contain carbon/silver to remove substances to improve taste; silver is antibacterial.
     • Pure water can be produced by distillation - expensive + lots of energy.
   • Chlorine: reduce microbes; linked to increase in cancer.
   • Flouride: reduce tooth decay/improve dental health; cause cancer + bone problems - also concern whether it's okay to mass medicate.