Carbonate Hardness
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Carbonate hardness, is a measure of the
water hardness Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...
caused by the presence of
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
() and
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemic ...
()
anions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
. Carbonate hardness is usually expressed either in degrees KH (
dKH Degrees of carbonate hardness (dKH or °KH; the K is from the German ''Karbonathärte'') is a Units of measurement, unit of Hard water, water hardness, specifically for temporary or carbonate hardness. Carbonate hardness is a measure of the conce ...
) (from the German ''"Karbonathärte"''), or in ''parts per million calcium carbonate'' ( ppm or grams per litre, mg/L). One
dKH Degrees of carbonate hardness (dKH or °KH; the K is from the German ''Karbonathärte'') is a Units of measurement, unit of Hard water, water hardness, specifically for temporary or carbonate hardness. Carbonate hardness is a measure of the conce ...
is equal to 17.848 mg/L (ppm) , e.g. one dKH corresponds to the carbonate and bicarbonate ions found in a solution of approximately 17.848 milligrams of calcium carbonate() per litre of water (17.848 ppm). Both measurements (mg/L or KH) are usually expressed as mg/L – meaning the concentration of carbonate expressed as if calcium carbonate were the sole source of carbonate ions. An
aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
containing 120 mg NaHCO3 (baking soda) per litre of water will contain 1.4285
mmol The mole, symbol mol, is the unit of amount of substance in the International System of Units (SI). The quantity amount of substance is a measure of how many elementary entities of a given substance are in an object or sample. The mole is define ...
/l of bicarbonate, since the
molar mass In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance which is the number of moles in that sample, measured in moles. The molar mass is a bulk, not molecular, p ...
of baking soda is 84.007 g/mol. This is equivalent in carbonate hardness to a solution containing 0.71423 mmol/L of (calcium) carbonate, or 71.485 mg/L of calcium carbonate (molar mass 100.09 g/mol). Since one degree KH = 17.848 mg/L CaCO3, this solution has a KH of 4.0052 degrees. Carbonate hardness should not be confused with a similar measure
Carbonate Alkalinity Carbonate hardness, is a measure of the water hardness caused by the presence of carbonate () and bicarbonate () anions. Carbonate hardness is usually expressed either in degrees KH (dKH) (from the German ''"Karbonathärte"''), or in ''parts per mi ...
which is expressed in either illi[equivalent.html" ;"title="quivalent.html" ;"title="illi[equivalent">illi[equivalent">quivalent.html" ;"title="illi[equivalent">illi[equivalentper litre (meq/L) or ppm. Carbonate hardness expressed in ppm does not necessarily equal carbonate alkalinity expressed in ppm. \text = [\text_3^-] + 2\times[\text_3^] whereas \text = [\text_3^-] + [\text_3^] However, for water with a pH below 8.5, the carbonate, CO32− will be less than 1% of the HCO3 so carbonate alkalinity will equal carbonate hardness to within an error of less than 1%. In a solution where only CO2 affects the pH, carbonate hardness can be used to calculate the concentration of dissolved CO2 in the solution with the formula CO2 = 3 × KH × 10(7-pH), where KH is degrees of carbonate hardness and CO2 is given in ppm by weight. The term ''carbonate hardness'' is also sometimes used as a synonym for
temporary hardness Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...
, in which case it refers to that portion of
hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...
that can be removed by processes such as boiling or
lime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnes ...
, and then separation of water from the resulting precipitate.


See also

* dGH or DGH or Degree of General Hardness, a measure of the hardness of water *
Hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...


References

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External links


Water Hardness definitions
Carbonates