Simple Description

Hard water contains ions which cause scum or limescale

Further Detail

Permenently hard water contains calcium or magnesium ions, these react with soap to form scum before the soap can lather. Temporary hard water contains hydrogen carbonate ions, when heated this decomposes to carbonate ions. If calcium ions are present calcium carbonate forms which deposits on the heating element. Ion exchange columns can be used to remove calcium or magnesium ions by replacing them with sodium ions.

Related Words:

• Soft water

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