Calcium and magnesium ions

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. 

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). 

Hardness The scale-forming and lather-inhibiting qualities which water, high in calcium and magnesium ions, possesses. 

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. 

Determination of calcium. Pipette two 25.0 mL portions of the mixed calcium and magnesium ion solution (not more than 0.01M with respect to either ion) into two separate 250 mL conical flasks and dilute each with about 25 mL of de-ionised water. To the first flask add 4 mL 8 M potassium hydroxide solution (a precipitate of magnesium hydroxide may be noted here), and allow to stand for 3-5 minutes with occasional swirling. Add about 30 mg each of potassium cyanide (Caution poison) and hydroxylammonium chloride and swirl the contents of the flask until the solids dissolve. Add about 50 mg of the HHSNNA indicator mixture and titrate with 0.01 M EDTA until the colour changes from red to blue. Run into the second flask from a burette a volume of EDTA solution equal to that required to reach the end point less 1 mL. Now add 4 mL of the potassium hydroxide solution, mix well and complete the titration as with the first sample record the exact volume of EDTA solution used. Perform a blank titration, replacing the sample with de-ionised water. 

Determination of total calcium and magnesium. Pipette 25.0 mL of the mixed calcium and magnesium ion solution into a 250 mL conical flask, dilute to about 50 mL with distilled water, add 5 mL of the buffer solution, and mix by... 

The presence of calcium and magnesium ions increases the adsorption of the surfactants at the water-air interface and leads to a corresponding lowering of the surface tension at the CMC as shown by the data in Table 4. A C16 branched AOS gives a lower surface tension than a linear C16 AOS this too is in agreement with other model studies and theoretical predictions [42, and Sec. 2 on interfacial tension). 

Nicholson, J. W., Wasson, E. A. Wilson, A. D. (1988). Thermal behaviour of films of partially neutralised poly(acrylic acid). 3. Effect of calcium and magnesium ions. British Polymer Journal, 20, 97-101. 

The sum of calcium and magnesium ions in the mud determines the total hardness. These ions are analyzed with complexometric titrations using EDTA (versenate). 

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. 

Tap water in some parts of the country contains large amounts of calcium and magnesium ions. The calcium usually enters the water as it seeps through limestone and chalk, since these rocks are sparingly soluble. 

A very important ligand (or chelating agent) for titrimetric analysis is the ethylenediaminetetraacetate (EDTA) ligand. It is especially useful in reacting with calcium and magnesium ions in hard water such that water hardness can be determined. The next section is devoted to this subject. 

Fig. 10.22. Chelating PCT sensors for calcium and magnesium ions (PCT-11 and PCT-12 Grynkiewicz G. et al. (1985) J. Biol. Chem. 260, 3440. PCT-13 and PCT-14 Haugland R. P., Handbook of Fluorescent Probes and Research Chemicals, 6th edn, Molecular Probes, Inc., Eugene, OR).

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