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hard water |
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Water that contains certain dissolved ions, most importantly calcium and magnesium ions, which cause it to lather poorly with soap, forming a scum. The hardness may be divided into two classes, temporary and permanent. Temporary hardness can be removed by boiling, which causes decomposition of hydrogencarbonate (bicarbonate) salts, as in the following equation, depositing a precipitate of the carbonate (causing scale):
Ca(HCO{TAG(tag=>sub)}3{TAG}){TAG(tag=>sub)}2{TAG}(aq) → CaCO{TAG(tag=>sub)}3{TAG}(s) + H{TAG(tag=>sub)}2{TAG}O(l) + CO{TAG(tag=>sub)}2{TAG}(g).
Permanent hardness cannot be removed by boiling; instead an ion-exchange resin must be used, which can also remove temporary hardness. |
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| Other Terms : anastigmatic lens | stereospecific reaction | rodent
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