Degrees of general hardness (dGH or °GH) is a
unit
Unit may refer to:
General measurement
* Unit of measurement, a definite magnitude of a physical quantity, defined and adopted by convention or by law
**International System of Units (SI), modern form of the metric system
**English units, histo ...
of
water hardness
Hard water is water that has a 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, bicar ...
, specifically of general hardness. General hardness is a measure of the concentration of
divalent
In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemica ...
metal ions such as
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
(Ca
2+) and
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
(Mg
2+) per volume of water. Specifically, 1 dGH is defined as 10 milligrams (mg) of
calcium oxide
Calcium oxide (formula: Ca O), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term '' lime'' connotes calcium-containing ...
(CaO) per litre of water. Since CaO has a
molar mass
In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...
of 56.08 g/mol, 1 dGH is equivalent to 0.17832
mmol per litre of elemental calcium and/or magnesium ions.
In water testing hardness is often measured in parts per million (ppm), where one part per million is defined as one milligram of
calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
(CaCO
3) per litre of water. Consequently, 1 dGH corresponds to 10 ppm CaO but 17.848 ppm CaCO
3 which has a molar mass of 100.09 g/mol.
See also
*
Carbonate hardness
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 pe ...
*
Hard water
Hard water is water that has a 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, bic ...
*
dKH
References
*
*
Units of measurement
Water chemistry
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