NCH ≈ (2×sulfate + chloride + nitrate) – (Na + K + ammonium)
On the other hand, strong bases are indicated by monovalent cations (e.g. Given a water analysis, strong acids manifest themselves in the presence of non-carbonate anions such like sulfate, chloride, nitrate. The non-carbonate hardness is a measure of the excess of strong acids over strong bases: (8) The non-carbonate hardness is – according to 4 – the difference of both quantities: (7)Ĭarbonate hardness is named temporary hardness because Ca and Mg carbonates precipitate as minerals upon heating, whereas Ca and Mg associated with sulfates, chlorides, or nitrates do not precipitate upon heating (therefore NCH is called permanent hardness).Īlternative Interpretation. carbonate hardness) are common water analysis parameters. The program calculates TH and CH, and displays both quantities in the output tables – as shown here.īoth total hardness and alkalinity (i.e. M alkalinity or total alkalinity) are synonyms: (6) This means that in water chemistry the terms carbonate hardness and alkalinity (i.e. While the total hardness in 1 is defined by the cationic content, there is also the opposite viewpoint taken from the anionic content, which divides the total hardness into carbonate hardness CH (temporary hardness) and non-carbonate hardness NCH (permanent hardness): (4)Ĭarbonate hardness is directly related to alkalinity: (5a) Total Hardness TH = Calcium Hardness + Magnesium Hardness Note: If the concentrations of Ca and Mg ions are expressed as “ppm CaCO 3”, 1a is also represented in the form: (3) The total hardness TH is used to classify aqueous solutions into four water-hardness categories. For example, it can be expressed in meq/L (SI units), or in ppm CaCO 3, or in German hardness degrees: (2a)Ġ.1339 × + 0.2307 × Ĭonversation rules to other units are given in the table below. There are several water hardness scales in use. 1 The correct formula is (according to its definition in 1): (1b) In practice, it is often used as the sum of the two most important freshwater cations, calcium and magnesium: (1a)īut this is only an approximation, albeit a good one. Total Hardness TH = Σ multivalent cations Total hardness is defined as the molar concentrations of all multi-valent cations in water (i.e.
There are different types of water hardness:
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