Magnesium solubility constant

Berner (1976) reviewed the problems of measuring calcite solubility in seawater, and it is these problems, in part, that have led to the use of stoichiometric solubility constants for calcite and aragonite (see Section 7.03.3). The most difficult problem is that, although the solubility of pure calcite is sought in experiments with seawater solutions, extensive magnesium co-precipitation can produce magnesian calcites. The solubility of these magnesian calcites differs from that of pure calcite. Thus, it is not possible to measure the solubility of pure calcite directly in seawater. 

Since the solubility of calcium carbonate is considerably less than that of magnesium carbonate, evaporation and concentration of salt lakes and lagoons must have produced calcium carbonate deposits initially. The brine would gradually be depleted of calcium ion and enriched with magnesium. Eventually, a condition would be reached where the brine concentration of the magnesium ion and carbonate exceeds the solubility constant of magnesite, and precipitation would proceed see Equation (2.2) ... 

Other. Insoluble alkaline-earth metal and heavy metal stannates are prepared by the metathetic reaction of a soluble salt of the metal with a soluble alkah—metal stannate. They are used as additives to ceramic dielectric bodies (32). The use of bismuth stannate [12777-45-6] Bi2(Sn02)3 5H20, with barium titanate produces a ceramic capacitor body of uniform dielectric constant over a substantial temperature range (33). Ceramic and dielectric properties of individual stannates are given in Reference 34. Other typical commercially available stannates are barium stannate [12009-18-6] BaSnO calcium stannate [12013 6-6] CaSnO magnesium stannate [12032-29-0], MgSnO and strontium stannate [12143-34-9], SrSnO. ... 

The solubility 5 of magnesium hydroxide (in units of moles per liter) can be computed from the equilibrium constant (the solubility product) for the dissolution of the salt. For 5 equal to the moles per liter of Mg(OH)2 dissolved ... 

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. 

Case III, An Excess of One Component Is Necessary.— It sometimes happens that an excess of one component is requisite for the formation of a double salt. Conversely, if the solid double salt is dissolved and the solution is evaporated, one of the components separates until the required excess of the other component has accumulated in the solution. This case is well illustrated by the mineral carnallite, KCl-MgCl2-6H20, one of the products of the Stassfurt mines. Let the point A (Fig. 20), represent a saturated solution of potassium chloride and the points, a saturated solution of magnesium chloride. An unsaturated solution of equivalent quantities of the two salts is then represented on the line OE, say at a. If the solution is evaporated at constant temperature (20°), the point a approaches the solubility curve of potassium chloride, viz., the line AC. At E, potassium chloride begins to separate and continues to do so until the representative point has moved to C, at which point carnallite makes its appearance. Since the separation of carnallite withdraws the two salts in equimolecular ratio from the solution, and since the solution now contains much more magnesium chloride than potassium chloride, the deposits of crystals of carnallite leave the solution unsaturated with respect to potassium chloride, and the latter salt steadily passes into solution again, while the deposit of carnallite increases. If, when the point C is reached, the crystals of potassium chloride are... 

In principle, it would be logical to combine plots of the buffer index curves of each of the buffer components of milk and thus obtain a plot which could be compared with that actually found for milk. It is not difficult, of course, to conclude that the principal buffer components are phosphate, citrate, bicarbonate, and proteins, but quantitative assignment of the buffer capacity to these components proves to be rather difficult. This problem arises primarily from the presence of calcium and magnesium in the system. These alkaline earths are present as free ions as soluble, undissociated complexes with phosphates, citrate, and casein and as colloidal phosphates associated with casein. Thus precise definition of the ionic equilibria in milk becomes rather complicated. It is difficult to obtain ratios for the various physical states of some of the components, even in simple systems. Some concentrations must be calculated from the dissociation constants, whose... 

Three approaches have been used in attempting to account for the buffer behavior of milk in terms of the properties of its components. These are calculation, fractionation, and titration of artificial mixtures. Whittier (1933A.B) derived equations for dB/dpH in calcium phosphate and calcium citrate solutions, taking into account available data on dissociation constants and solubility products. Presumably this approach could be extended to calculate the entire buffer curve. It demands precise knowledge of the dissociation constants of the several buffers, the dissociation of the calcium and magnesium complexes, and the solubility products of the calcium and magnesium phosphates under the conditions of a titration of milk. 

Soluble Salts Boil 10 g of sample with 150 mL of water for 15 min. Cool to room temperature, and add water to restore the original volume. Allow the mixture to stand for 15 min, and filter until clear. Reserve 20 mL of the filtrate for the test for Free Alkali (above). Add 25 mL of water to 75 mL of the clear filtrate. Evaporate 50 mL of this solution, representing 2.5 g of magnesium silicate, in a tared platinum dish on a steam bath to dryness, and ignite gently to constant weight. The weight of the residue does not exceed 75 mg. 

PROBLEM Magnesium hydroxide has a solubility product constant of 1.8 x 10-11 at 298 K. Write the equilibrium constant expression for this salt. What is the concentration of magnesium and hydroxide ions in a saturated... 

PbS04 is more soluble because it has a greater solubility product constant than that of magnesium hydroxide. 

Tin tribenzyl chloride. — The first preparation of this compound was made by adding stannic chloride (1 moL) to ice-cold magnesium benzyl chloride (3 mols.) in dry ether, but the yield was poor. In Kipping s method the stannic chloride and magnesium are mixed in dry ether, prior to the addition of the benzyl chloride, this method giving a 60 per cent, yield- The crude product is recrystallised from acetone, and then from glacial acetic acid, until the melting-point is constant. It forms well-defined prisms, M.pt. 143 to 145 C., readily soluble in acetone, benzene, or chloroform, less so in ether or alcohol, and insoluble in water. With 1 mol. of iodine it reacts as follows —... 

Nature, however, has provided us with a long-term solubility experiment. The well waters of Florida show a constant ratio of magnesium to calcium ([Mg ]/[Ca ] = 0.8 0.1). The tendency for subsurface waters to have such a nearly constant magnesium-calcium ratio suggests that waters in porous dolomitic limestones might have equilibrated with both the calcite and dolomite phases [For a general treatment on dolomites in groundwaters, see, for example, Plummer et al. (1990).]... 

Though slightly soluble hydroxides are not salts, they have solubility product constants. Magnesium hydroxide is an example. 

Properties Dark, reddish-brown liquid irritating fumes.Bp 58.8C, fp-7.3C, d 3.11 (20/4C), vap d vs. air (at 15C) 5.51, wt/gal 25.7 lb, specific heat 0.107 cal/g, refr index 1.647, dielectric constant 3.2. Soluble in common organic solvents very slightly soluble in water. Attacks most metals, including platinum and palladium aluminum reacts vigorously and potassium explosively. Dry bromine does not attack lead, nickel, magnesium, tantalum, iron, zinc, or (below 300C) sodium. 

Gelbach and King [42GEL/K1N] prepared their specimen of Ag2Se04(s) by slow precipitation from 10% silver nitrate and magnesium selenate solutions. The solubility in six solutions of selenic acid in the concentration range from 0.00 to 0.12 M was determined. Equilibrium was approached from under- as well as supersaturation. The solubility in water was found to be 2.42 x 10 M. No solubility product was calculated from the data. This has been done here with log K° = 1.75 for the protonation constant... 

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