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Soft water is water that lathers easily with soap.  Hard water uses more soap to produce lather and to wash effectively.  This is because hard water contains more dissolved compounds that react with soap to form scum - an insoluble solid.  Soapless detergents do not react with hard water to produce scum.

When water is in contact with rocks, some compounds dissolve.  If the water contains dissolved calcium or magnesium ions, these will react with the soap to form scum and so the water is hard.  When it is heated, temporary hard water produces an insoluble solid called scale.  Scale can be deposited in kettles, boilers and pipes, reducing the efficiency of heating systems and causing blockages.

Calcium compounds are good for our health because they help to develop strong bones and teeth.  Calcium can also reduce the risk of heart disease.


Soft water may contain dissolved substances, but it doesn't contain dissolved salts that will react with soap to form scum.  Soft water doesn't produce scale when it is heated.  Hard water can be made soft by removing the dissolved calcium and magnesium ions.  Some types of hard water are affected by heating and others aren't.  Temporary hard water is softened by boiling because when it is heated the calcium and magnesium compounds form insoluble scale, thus removing them from the water.  Permanent hard water isn't softened by boiling and doesn't produce scale when heated.  

Temporary hard water contains hydrogencarbonate ions, HCO3 - (aq).  The hydrogencarbonate ions decompose when…


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