Hard Water

Water that contains dissolved calcium ions.

Temporarily Hard Water

CaCO3 (s) + CO2 (g) + H2O (l) Ca(HCO3)2 (aq)

limestone hard water

Temporary hardness can be removed by boiling:

heat Ca(HCO3)2 (aq) CaCO3 (s) + CO2 (g) + H2O (l) “scale”

stalagmites &stalactites

Advantages of Hard Water

Calcium ions are needed for

healthy bones, muscle

contraction, & blood-clotting.

Soap is less effective in hard waterbecause the calcium ions react withthe stearate ions in soap to form aprecipitate, calcium stearate(“soap scum”).

Disadvantages of Hard Water

When temporarily hard water is heated, calcium carbonate (“scale”) is formed. This solid can reduce the efficiency of tea kettles and block hot water pipes.