Magnesium in water

Ion exchange zeolites are builders in washing powder, where they have gradually replaced phosphates to bind calcium. Calcium and, to a lesser extent, magnesium in water are exchanged for sodium in zeolite A. This is the largest application of zeolites today. Zeolites are essentially nontoxic, and pose no... 

It has frequently been suggested that the organisers of interlaboratory certification studies should only accept reliable laboratories as participants and one obvious selection criterion would be to use only accredited laboratories. However, an evaluation of data obtained from several studies organised by LGC over the past 7 years indicates that accredited laboratories are not necessarily more reliable than nonaccredited laboratories. For example, Fig. 1 shows that in an interlaboratory study to determine magnesium in water, accredited laboratories (marked with an asterisk) were just as likely to produce results with a large deviations as nonaccredited laboratories. 

The technique for the determination of calcium and magnesium in waters and effluents is described below and is based on that reported in HMSO [16,17]. 

Capillary electrophoresis Capillary electrophoresis (CE) is used to analyze sodium, potassium, calcium, and magnesium in water samples. The detection is conducted by reverse absorbance measurements. Sufficient separation of the four cations is established with an electrolyte solution of 5 mM imidazole/6.5 mM a-hydroxyisobutyric acid/2 mM 18-crown-6 ether of pEI 4.1 [42]. CE with a contactless conductometric detector is used to determine small anions and cations in water samples from different sources. 2-(N-Morpholino)ethanesulfonic acid/histidine-based (Mes/Elis) electrolytes are used for direct conductivity detection of anions and cations, while ammonium acetate is used for indirect conductivity determination of alkylammonium salts. Eor the simultaneous separation procedure, involving dual-opposite end injection, an electrolyte consisting of 20 mM Mes/EIis, 1.5 mM 18-crown-6 and 20 mM cetyltri-methylammonium bromide provides baseline separation of 13 anions and cations in less than 6 min [43]. Also CE with a capacitively coupled... 

Figure 7 shows the results in the analysis of magnesium in water, where the precision with the premix burner is slightly better. However, a different lamp was used here with each burner so some or all of this difference could be attributable to a difference in the lamps. The older three burner set was rechecked with no improvement in precision. The effect that the hollow cathode lamp can have on precision can be seen in Figure 8, where two different lamps were used with the premix burner... 

Calcium and magnesium are commonly found in water. Obviously if this assay is to be used with water samples, EDTA must be added. It must be determined using water uncontaminated with organic toxins how much EDTA must be used to compensate for the divalent cations. Often the concentration of divalent cations is determined by atomic absorption spectroscopy. However, these values do not agree with the toxicity relieved by EDTA. Soil samples witii as much as 5 gm calcium (45 mM) per kg soil have been assayed using 2.5 imoles EDTA in each sample (Hillaker, 1996). The calcium is complexed with sulfate and phosphate ions and the calcium is not available to the cell, is not seen by the mechanism that reduces the dye. Levels of soluble calcium and magnesium in water are very low. We have found that 2.5 (imoles of EDTA relieves the inhibition caused by divalent cations in all water and soil samples tested thus far (Botsford, 2000b). 

Thus, lead immersed in sulfuric acid, or magnesium in water, or iron in inhibited pickling acid, would be called passive by Def. 2 based on low corrosion rates, despite pronounced corrosion tendencies but these metals are not passive by Def. 1. Their corrosion potentials are relatively active, and polarization is not pronounced when they are made the anode of a cell. 

Fig. 5 A sample Pourbaix diagram of magnesium in water the dashed blue lines represent the potentials at which water is oxidized (top line) and reduced (bottom line). Reprinted with permission from [43]. Copyright 2012 American Chemical Society...

The ions involved in water hardness, a measure of the total concentration of calcium and magnesium in water, are readily titrated at pH 10 with a solution of EDTA, a chelating agent mentioned as a titrant for metals in Chapter 25, Section 25.6. The titration reaction is... 

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

These can be prepared by electrolytic oxidation of chlorates(V) or by neutralisation of the acid with metals. Many chlorates(VII) are very soluble in water and indeed barium and magnesium chlorates-(VII) form hydrates of such low vapour pressure that they can be used as desiccants. The chlorate(VII) ion shows the least tendency of any negative ion to behave as a ligand, i.e. to form complexes with cations, and hence solutions of chlorates (VII) are used when it is desired to avoid complex formation in solution. 

The chromates of the alkali metals and of magnesium and calcium are soluble in water the other chromates are insoluble. The chromate ion is yellow, but some insoluble chromates are red (for example silver chromate, Ag2Cr04). Chromates are often isomorph-ous with sulphates, which suggests that the chromate ion, CrO has a tetrahedral structure similar to that of the sulphate ion, SO4 Chromates may be prepared by oxidising chromium(III) salts the oxidation can be carried out by fusion with sodium peroxide, or by adding sodium peroxide to a solution of the chromium(IIl) salt. The use of sodium peroxide ensures an alkaline solution otherwise, under acid conditions, the chromate ion is converted into the orange-coloured dichromate ion ... 

Place 8 0 g. of magnesium turnings or ribbon and 80 ml. of the dry benzene in the flask. Prepare a solution of 9-0 g. of mercuric chloride in 50 ml. of the dry acetone, transfer it to the dropping-funnel, and then allow it to enter the flask slowly at first, and then more rapidly, so that the addition takes about 3-5 minutes. The reaction usually starts shortly after the initial addition of the mercuric chloride solution if it is delayed, it may then start vigorously, and the flask may have to be cooled in water to prevent escape of acetone through the condenser. 

Bcamples of metal-ion catalysed organic reactions in water where the catalyst acts exclusively as Lewis acid are the hromination of diketones" " and the decarboxylation of oxaloacetate. The latter reaction has been studied in detail. In 1941 it was demonstrated that magnesium(II) ions catalyse this reaction" Later also catalysis by other multivalent metal ions, such as Zn(II), Mn(II), Cu(II), Cd(ir), Fe(II), Pb(II), Fe(III)... 

A solution of 0.21 mol of butyllithium in about 140 ml of hexane (note 1) was cooled below -40°C and 90 ml of dry THF ivere run in. Subsequently a cold (< -20 C) solution of 0.25 nol of propyne in 20 ml of dry THF was added with cooling below -20°C and a white precipitate was formed. A solution of 0.10 mol of anhydrous (note 2) lithium bromide in 30 ml of THF was added, followed by 0.20 mol of freshly distilled cyclopentanone or cyclohexanone, all at -30°C. The precipitate had disappeared almost completely after 20 min. The cooling bath was then removed and when the temperature had reached 0°C, the mixture was hydrolyzed by addition of 100 ml of a solution of 20 g of NHi,Cl in water. After shaking and separation of the layers four extractions with diethyl ether were carried out. The extracts were dried over magnesium sulfate and the solvents removed by evaporation in a water--pump vacuum. Careful distillation of the remaining liquids afforded the following... 

Standard Magnesium Solution. Dissolve 24.647 g of magnesium sulfate heptahy-drate in water and dilute to 1 E for O.lAf solution. 

Magnesium sulfate, epsom salts, MgS04 7H2O—0.5N 62 g per liter saturated solution dissolve 600 g of the salt in water and dilute to 1 liter. 

Properties. Lithium fluoride [7789-24-4] LiF, is a white nonhygroscopic crystaUine material that does not form a hydrate. The properties of lithium fluoride are similar to the aLkaline-earth fluorides. The solubility in water is quite low and chemical reactivity is low, similar to that of calcium fluoride and magnesium fluoride. Several chemical and physical properties of lithium fluoride are listed in Table 1. At high temperatures, lithium fluoride hydroly2es to hydrogen fluoride when heated in the presence of moisture. A bifluoride [12159-92-17, LiF HF, which forms on reaction of LiF with hydrofluoric acid, is unstable to loss of HF in the solid form. 

Alagnesium Oxide. Magnesia [1309-48 ] MgO, is available in a very bulky white powder known as light magnesium oxide, or a relatively dense white powder known as heavy magnesium oxide. It absorbs moisture and carbon dioxide when exposed to air. It is practically insoluble in water, insoluble in alcohol, and soluble in dilute acids (see Magnesium compounds). 

Gum ghatti is the calcium and magnesium salt of a complex polysaccharide which contains L-arabinose, D-galactose, D-mannose, and D-xylose and D-glucuronic acid (48) and has a molecular weight of approximately 12,000. On dispersion in water, gum ghatti forms viscous solutions of viscosity intermediate between those of gum arabic and gum karaya. These dispersions have emulsification and adhesive properties equivalent to or superior to those described for gum arabic. 

Data on the solubihty of magnesium hydroxide in water are not all in agreement, but the solubihty is extremely low. The extent of Mg(OH)2 solubihty is 10 mg/L, which is about 1/100 the solubihty of Ca(OH)2. In concentrated solutions of NH Cl and NH CO, the solubihty of Mg(OH)2 is markedly increased, but in no instance does its solubihty equal that of MgCO in water heavily permeated with CO2. Dolomitic hydrates are slightly less soluble than high calcium hydrates, but much nearer the latter in value than Mg(OH)2, because the presence of MgO and Mg(OH)2 does not impede the dissolution of its Ca(OH)2 constituent. 

Metallic magnesium and water [7732-18-5] react. Under normal atmospheric conditions or in pure or chloride-free water of high pH, the reaction is suppressed by the formation of an insoluble magnesium hydroxide [1309-42-8] film. 

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