Inorganic reactions
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How is carbon dioxide involved in the formation of hard water?
Ulex writes
Rocks containing calcium carbonate such as limestone and some types of sandstone (where the silica grains are held together with calcium carbonate) react with water and atmospheric carbon dioxide to give calcium hydrogencarbonate. This, unlike the calcium carbonate from which it is formed, is soluble in water and its solution contains calcium ions which are responsible for the hardness of water.
CaCO3(s) + H2O(l) + CO2(g) -> Ca(HCO3)2 (aq)
This equation is reversible so that if the hard water is boiled, carbon dioxide is liberated and calcium carbonate is precipitated – the so-called limescale which coats the insides of hot water pipes in hard-water areas.
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updated: 24 January 2006
