Hardness in water

The hydrogencarbonate ion, produced in nature by this reaction, is one of the main causes of temporary hardness in water. Carbon dioxide is fairly soluble in water, 1 cm dissolving 1.7 cm of the gas at stp. The variation of solubility with pressure does not obey Henry s law, since the reaction... 

Magnesium and calcium hydrogencarbonates are known in solution and are responsible for temporary hardness in water. 

If the hydrogencarbonate is in solution and the cation is Ca or Mg. the insoluble carbonate is precipitated this reaction may be used, therefore, to remove hardness in water by precipitation of Ca or Mg ions.) The ease of decomposition of hydrogencar-bonates affords a test to distinguish between a hydrogencarbonate and a carbonate carbon dioxide is evolved by a hydrogencarbonate, but not by a carbonate, if it is heated, either as the solid or in solution, on a boiling water bath. 

METHODS FOR REMOVING THE METAL IONS RESPONSIBLE FOR HARDNESS IN WATER... 

The solubility of the carbonate in water containing carbon dioxide causes the formation of caves with stalagtites and stalagmites and is responsible for hardness in water. Other important compounds are the carbide, chloride, cyanamide, hypochlorite, nitrate, and sulfide. 

The dealkalization process removes the temporary hardness in water. This uses an acid resin bed for regeneration—in this case sulfuric acid (H2SO4). 

Hardness in water varies widely, and as an arbitrary classification ... 

Recently developed softening membranes reject most of the hardness in water while passing sodium salts, and operate at pressures of about 5 bar. This can be used to provide substantially softened make-up water for shell... 

A laboratory check is normally desirable to assess the amounts of organic and mineral acids present, and a check on hardness is usually necessary in any case. Hardness in water is due to dissolved salts - mainly of calcium, magnesium and iron, and occasionally of aluminum. Softening may be required if the water is extremely hard, because the salts react with the emulsifier in the soluble oil to form an insoluble scum that floats on the surface of the emulsion. The scum may not in itself be harmful, but its formation uses up some of the emulsifier and causes the emulsion to be unstable. 

Hardness in water (soap-consuming scum and scale-generating salts) is caused by the presence of bicarbonates, carbonates, and... 

Goetz, C. A., T. C. Loomis and H. Diehl Total hardness in water stability of standard disodium dihydrogen cthylenediaminctetraacetate solutions. Analytic. Chem. 22, 798 (1950). 

The problematic agent in this list are builders, compounds that sequester ("capture") mineral ions such as calcium and magnesium that would otherwise reduce the sudsing properties of a cleaning agent. One of the most effective builders ever discovered, and one that was widely used for many years, is sodium tripolyphosphate (TPP). The structure of this molecule is such that it can surround and trap ions (such as Ga "" and Mg "") that are responsible for the "hardness in water (which reduces the effectiveness of a detergent). 

Hardness in water can be divided into two types - temporary and permanent. Temporary hardness is caused by the presence of dissolved calcium or magnesium hydrogencarbonates. Temporary hardness is so called because it is easily removed by boiling. 

The amount of soap required to just produce a lather with the hard water can be used to estimate the hardness in water. 

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaC03/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as carbonate hardness and noncarbonate hardness. This can be determined from alkalinity. The relationship is as follows ... 

Temporary hardness. Probably because of the ease with which, these impurities may be removed, the acid carbonates of calcium and magnesium (and in some cases ferrous iron) are said to constitute temporary hardness in water. This type of hardness may be removed by boiling the water, whereupon the soluble acid carbonates are converted to the insoluble normal carbonates, which may be removed by filtration ... 

A very soft water has a slimy feel. For example, rainwater, which is exceedingly soft, is slimy when used with soap. For this reason, hardness in water used for domestic purposes is not completely removed. Hardness is normally removed to the level of 75 to 120 mg/L as CaCO. ... 

Polyoxyl 40 hydrogenated castor oil (Cremophor RH 40) and polyoxyl 60 hydrogenated castor oil are largely unaffected by the salts that cause hardness in water. Cremophor RH 40 was found to prolong the dissolution time of digoxin tablets. ... 

Because all but the first two compounds are usually present in insignificant concentrations in natural waters, hardness is defined as a characteristic of water that represents the total concentration of just the calcium and magnesium ions expressed as calcium carbonate. The main salts responsible for hardness in waters are the hydrogen carbonates (bicarbonates) and the sulfates of calcium and magnesium. If water is brought to a boil, the bicarbonates decompose, some of the COj boils away, and the rest forms insoluble precipitates. Because the carbonates can be removed, this is... 

USE As acid-base indicator in 0.2% soln in alcohol. pH 4.4 red 6.4 blue. Satisfactory for titrating mineral acids, strong bases, many alkaloids determining alkalinity and temporary hardness in water analysis. Biological stain dye for wool, silk- Not adapted for carbonates, weak inorganic and organic acids, weak bases. Lacmoid is more sensitive than litmus, particularly in form of test paper. 

Clarke s soap solution (estimation of hardness in water). 

Soap solution (reagent for hardness in water). Dissolve 100 g of dry castUe soap in 1 L of 80% alcohol (5 parts alcohol to 1 part water). AUow to stand several days and dUute with 70% to 80% alcohol untU 6.4 mb produces a permanent lather with 20 mb of standard calcium solution. The latter solution is made by dissolving 0.2 g of CaCO in a small amount of dUute HCl, evaporating to dryness and making up to 1 L. 

Hardness in water increases the amount of soap required to produce a lather. It is largely caused by dissolved calcium and magnesium salts, of which the most common are ... 

Non-carbonate hardness is hardness in water caused mainly by calcium and magnesium compounds other than the bicarbonates. 

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