Water - Solubility - Ions
Hardness of Water.
is said to be hard if it doesn't form a lather
with soap. Calcium and magnesium ions cause water to be hard.
Hardness is described as "permanent" or "temporary".
water is naturally acidic due to dissolved
(see the Carbon Cycle).
The acid in rain water is carbonic acid, H2CO3(aq).
containing magnesium carbonate or
calcium carbonate (limestone), will react
with dilute carbonic acid forming hydrogencarbonates.
acid + calcium
carbonate calcium hydrogencarbonate.
H2CO3(aq) + CaCO3(s) Ca(HCO3)2(aq)
acid + magnesium
carbonate magnesium hydrogencarbonate.
H2CO3(aq) + MgCO3(s) Mg(HCO3)2(aq)
These hydrogencarbonates are
slightly soluble in water, causing hardness.
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