Magnesium/ions/salts

The magnesium ion having a high hydration energy (Table 6.2) also shows hydrolysis but to a lesser extent (than either Be or AF ). The chloride forms several hydrates which decompose on heating to give a basic salt, a reaction most simply represented as (cf. p. 45) ... 

Other Reactions of Phospholipids. The unsaturated fatty acid groups in soybean lecithin can be halogenated. Acetic anhydride combined with the amino group of phosphatidylethanolamine forms acetylated compounds. PhosphoHpids form addition compounds with salts of heavy metals. Phosphatidylethanolamine and phosphatidjhnositol have affinities for calcium and magnesium ions that are related to interaction with their polar groups. 

Ammonium chloride [12125-02-9], ammonium sulfate [7783-20-2], and diammonium phosphate [7708-28-0] have also been used for shale stabilization (102,103). Ammonium ions have essentially the same effect on shales as potassium ions but use of ammonium salts is often objectionable because of the alkaline nature of the mud. In the North Sea and northern Europe, where magnesium-bearing salt formations ate encountered, magnesium chloride [7786-30-3] is used, but in the United States it is used only on a small scale. 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

The ester is washed thoroughly in iron-free water to remove acid and any desirable salts these wash Hquids are sent for acid recovery. The final wash may contain some sodium, calcium, or magnesium ions to stabilize traces of sulfate esters remaining on the cellulose acetate. 

Basically, the hardness salts of calcium and magnesium ions are ex changed for sodium ions in the dealkization process the carbonate and bicarbonate salts, which cause high levels of alkalinity, are replaced with chloride ions. Reverse osmosis can also be used to produce demineralized water. 

Early experimental work in electrorefining at Los Alamos by Mullins et-all ) demonstrated that americium could be partitioned between molten plutonium and a molten NaCl-KCl salt containing Pu+3 ions, and Knighton et-al(8), working at ANL on molten salt separation processes for fuel reprocessing, demonstrated that americium could be extracted from Mg-Zn-Pu-Am alloys with immiscible molten magnesium chloride salts. Work... 

It is sometimes possible to separate different cations from a solution by adding a soluble salt containing an anion with which they form insoluble salts. For example, seawater is a mixture of many different ions. It is possible to precipitate magnesium ions from seawater by adding hydroxide ions. However, other cations are also present in seawater. Their individual concentrations and the relative solubilities of their hydroxides determine which will precipitate first if a certain amount of hydroxide is added. Optimum separation of two compounds is achieved when Qsp exceeds the Ksp of one species but is less than the Ksp of the second species. Example 11.11 illustrates a strategy for predicting the order of precipitation. 

Many ionic compounds contain what used to be referred to as water of crystallization . For example, magnesium chloride can exist as a fully hydrated salt which was formerly written MgCla.bHjO, but is more appropriately written Mg(OH2)eCl2, since the water molecules occupy coordination sites around the magnesium ions. This is typical. In most compounds that contain water of crystallization, the water molecules are bound to the cation in an aquo complex in the manner originally proposed by Alfred Werner (1866-1919) in 1893 (Kauffman, 1981). Such an arrangement has been confirmed in numerous cases by X-ray diffraction techniques. 

If S moles of CaCC>3 dissolve in a liter of water, then S moles each of calcium ion and carbonate ion form. With these ion concentrations equal to S, the solubility of CaCC>3 is calculated as 9.3 x 10 5 M. The higher solubility of magnesium carbonate in water, 6.3 x 10 3 M, results from the larger solubility product constant. Nevertheless, both of these carbonate salts are rather insoluble, and the excess carbonate anions provided by the sodium carbonate effectively precipitate the calcium and magnesium ions from solution. 

The chemiluminescence technique has been used to determine trivalent chromium in seawater. Chang et al. [187] showed Luminol techniques for determination of chromium (III) were hampered by a salt interference, mainly due to magnesium ions. Elimination of this interference is achieved by seawater dilution and utilising bromide ion chemiluminescence signal enhancement (Fig. 5.7). The chemiluminescence results were comparable with those obtained by a graphite furnace flameless atomic absorption analysis for the total chromium present in samples. The detection limit is 3.3 x 10 9 mol/1 (0.2 ppb) for seawater with a salinity of 35%, with 0.5 M bromide enhancement. 

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