1. Hard Water Water that contains dissolved calcium ions.

2. Temporarily Hard Water CaCO 3 (s) + CO 2 (g) + H 2 O (l)  Ca(HCO 3 ) 2 (aq) limestone hard water Temporary hardness can be removed by boiling: heat Ca(HCO 3 ) 2 (aq)  CaCO 3 (s) + CO 2 (g) + H 2 O (l) “scale” stalagmites & stalactites

3. Advantages of Hard Water Calcium ions are needed for healthy bones, muscle contraction, & blood-clotting.

4. Soap is less effective in hard water because the calcium ions react with the stearate ions in soap to form a precipitate, 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.