Chemistry Unit 3: Water

There are 2 types of hard water:

• Temporary hardness - which contains hydrogen carbonates
• Permanent hardness - which contains dissolved calcium sulphate

Hard water is caused by calcium and magnesium ions. 

These dissolve into the water when water flows over rocks like limestone, chalk and gypsum.

Whether you have hard water or soft water depends on the rocks in your area.

• When mixed with soap, soft water easily forms a lather, but, hard water forms scum, this means you have to use more soap to form a lather 
• When heated, hard water forms scale (calcium carbonate) which builds up in kettles, pipes and boilers etc., this reduces efficiency, which means things may need to be cleaned or replaced. 

 Benefits of hard water:

• Calcium ions are good for healthy teeth and bones
• Studies have found that people living in areas with hard water are at a lesser risk of developing heart disease than people in soft water areas.

• Temporary hardness is removed by boiling. When heated the calciumhydrogencarbonate decomposes to form calcium carbonate (limescale) which is insoluble.
• Both types of water hardness can be softened by adding washing soda (sodium carbonate). The added carbonate ions react with the calcium and magnesium ions to make  insoluble precipitate. 
• Both types of water hardness can be softened by running the water through ion exchange columns. These columns contain sodium/hydrogen ions which are exchanged for the calcium or magnesium ions that make the water hard.

You can use titration to compare the hardness of water samples.

Method:

1) Fill a burette with a fixed volume of soap solution

2) Fill a flask with a fixed volume of water 

3) Add 1cm (cubed) of soap solution, but a bung in the flask and shake for 10 seconds.

4) Repeat step 3 until a lasting lather is formed (lasts for 30 seconds)

5) Record and test different samples