Calcium ions, in water

As a sequestering agent, it attaches to calcium ions in water, which keeps them from interfering with detergents and soaps. 

Figure 10.17 Flow schematic of electrodialysis systems used to exchange target ions in the feed solution, (a) An all-cation exchange membrane stack to exchange sodium ions for calcium ions in water softening, (b) An all-anion exchange membrane stack to exchange hydroxyl ions for citrate ions in deacidification of fruit juice...

The presence of magnesium and calcium ions in water makes the water hard. Explain in terms of solubility why the presence of these ions is often undesirable. Find out what measures can be taken to eliminate them. 

Sodium C rbon te. Sodium carbonate softens water by forming insoluble calcium carbonate with calcium ions in hard water. Carbonate can also reduce calcium levels by ion pairing, although the benefit to detergency is questionable. Buildup of calcium carbonate on machine and fabrics, which can occur with time, is undesirable. Sodium carbonate [497-19-8] does not provide any suspending action. It does, however, provide alkalinity to the wash hquor and is an effective alkah. 

Calcium ions in seawater muds can be controlled and removed by forming insoluble precipitates accomplished by adding alkalis such as caustic soda, lime, or barium hydroxide. Soda ash or sodium bicarbonate is of no value in controlling the total hardness of sea water. 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

The action of carbonic acid on limestone produces a calcium bicarbonate solution that is exceedingly soluble in water. (For comparison, at 20°C the solubility of calcium carbonate in water is only 0.0145 g per liter while the solubility of calcium bicarbonate is 166 g per literJ ) Magnesium ions from dolomite are also released into aqueous solution according to the same mechanism. The weathering of gypsum, calcium sulfate, also releases calcium ions into natural water supplies. 

The modern history of ion exchange began in about 1850 when two English chemists, Thompson(4) and Way(5), studied the exchange between ammonium ions in fertilisers and calcium ions in soil. The materials responsible for the exchange were shown later to be naturally occurring alumino-silicates 6. History records very much earlier observations of the phenomenon and, for example, Aristotle(7), in 330 BC, noted that sea-water loses some of its salt when allowed to percolate through some sands. Those who claim priority for Moses(8) should note however that the process described may have been adsorption ... 

It is generally considered dial aldosterone, and to some extent the other honnnnes. have a regulatory effect upon the metabolism of electrolytes and water, particularly upon the concentration of the ions of the alkali metals in intracellular lluids. Administration of steroids also increases the concentration of calcium ions in those fluids. However, all three of these hormones have a number of other effects, roughly in the order of potency—cortisol, corticosterone, aldosterone. They produce changes in the metabolism of carbohydrates, proteins, and fats. 

It is well known that the AOM process involves a transfer of electrons from methane to sulfate, producing bicarbonate and sulfide in equimolar amounts, which in-turn react with hydronium and calcium ions in the water, to produce the overall reaction ... 

Causes kettles to fur Calcium ions in hard water are required by the body for bones and teeth... 

Hardness of water This is caused by the presence of calcium (or magnesium) ions in water, which form a scum with soap and prevent the formation of a lather. There are two types of hardness ... 

Bases that produce hydroxide ions in solution turn phenolphthalein red. Calcium and magnesium produce hydroxide ions in water. The following equations symbolize the reactions ... 

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 ... 

We have also recently discovered that added calcium laurate is able markedly to enhance the mechanical stability of natural rubber latex (2.). This observation is surprising, partly because of the low solubility of calcium laurate in water, and partly because calcium ions are known to be powerful destabilisers of natural rubber latex (j ). It indicates that the stabilising effect of the laurate anion is much greater than the destabilising effect of the calcium cation. 

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