Hard & Soft Water

• Water is either soft or hard.

• To find out which type of water hardness it is, add soap to the water & shake - 

Soft water = large amount of bubbles (lather)

Hard water = few bubbles on surface (scum)

• Water hardneness is caused by dissolved magnesium ions or calcium ions.

• There are two types of hard water -

a) temporary hard water

b) permanent hard water

• Removed by boiling the water.

• Caused by dissolved magnesium hyrdogen carbonate or calcium hydrogen carbonate.

• When the water it boiled the compounds decompose (thermal decomosition reaction).

• Calcium hydrogen carbonate → calcium carbonate + water + carbon dioxide

Ca(HCO3) → CaCO3 + H20 +CO2

white precipiate is made

• Calcium / magnesium carbonate are both insoluble white solids = limescale

• This can not be removed by boiling.

• Caused by dissolved calcium sulfate or magnessium sulfate.

• It is removed by two compounds (both also remove temporary hard water).

1. Ion Exchange Resin (IER)

Hard water → IER → Soft water

IER traps the Calcium / Magnesium sulfate & replaces them with Sodium that does not cause water hardness.

The IER will eventually run out of Sodium & stop working.

To get the IER working, wash with Sodium chloride solution & this will replace the lost Sodium.

2. Add Sodium carbonate solution (washing soda)

• This causes a precipiate reaction.

• Sodium carbonate + Calcium sulfate → Calcium carbonate + Sodium sulfate

Na2CO3 (aq) + CaSO4 (aq) → CaCO3 (s) + Na2SO4 (aq)

Calcium carbonate = white precipiate

Boiling the Water:

• only works to temporary hard water
• forms limescale that blocks filters & pipes
• works every time

Ion Exchange Resin:

• resin will stop working when the Sodium runs out
• have to wash with Sodium chloride solution
• works for temporary & permanent hard water
• no limescale is made

Advantges of Hard water:

• good for the bones & teeth
• reduces risks of heart disease

Disadvantages of Hard Water:

• problems can occur in the filters & pipe with blockages