Degrees of general hardness (dGH or °GH) is a
unit
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* ''Unit'' (alb ...
of
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 ...
, 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 element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
Description
The combining capacity, or affinity of an ...
metal ions such as
calcium
Calcium is a chemical element with the 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 ...
(Ca
2+) and
magnesium
Magnesium is a chemical element with the 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 of the periodic ta ...
(Mg
2+) per volume of water. Specifically, 1 dGH is defined as 10 milligrams (mg) of
calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, Caustic (substance), caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime (material), lime''" co ...
(CaO) per litre of water. Since CaO has a
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 56.08 g/mol, 1 dGH is equivalent to 0.17832
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 ...
per litre of elemental calcium and/or magnesium ions.
In water testing, paper strips often measure hardness in parts per million (ppm), where one part per million is defined as one milligram of
calcium carbonate (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 per mi ...
*
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 ...
*
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 ...
External links
Water Hardness definitionsWater hardness calculator
Units of measurement
Water chemistry
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