Water Solutes

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Hard Water

In some parts of Britain, the water supply passes through rocks and collects dissolved compounds or minerals to form solutions.

Minerals containing calcium and magnesium ions make the water hard.

The amount of solute dissolved in a volume of a solution is called its concentration.



You can calculate the concentration of a solution using this equation:


concentration= amount of solute (g) / volume of solution in dm3

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Problems with hard water

If you try to wash with soap in hard water, it will be difficult to make a lather.

This is because the calcium and magnesium ions in the water, combine with the soap to form an insoluble precipitate. This is scum on the surface of the water.

You have to add more soap to make the magnesium and calcium ions react to make scum, before you can make a lather.


Disadvantages of this:

  • Some soap is then wasted
  • scum has to be removed in water treatment works.
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