Calcium ions, dissolution

CaC03(s) Calcium carbonate (limestone) - Precipitation- Ca2+ Calcium ion dissolution reactions + CO - Carbonate ion -8.3b 11.6... 

The Ca(Il) coaceatratioa ia blood is closely coatroUed aormal values He betweea 2.1 and 2.6 mmol/L (8.5—10.4 mg/dL) of semm (21). The free calcium ion concentration is near 1.2 mmol/L the rest is chelated with blood proteias or, to a lesser extent, with citrate. It is the free Ca(Il) ia the semm that determines the calcium balance with the tissues. The mineral phase of bone is essentially ia chemical equiUbrium with calcium and phosphate ions present ia blood semm, and bone cells can easily promote either the deposition or dissolution of the mineral phase by localized changes ia pH or chelating... 

Soaps are composed of sodium salts of various fatty acids. These acids include those with the general structure CH3-(CH2) -COOH where n = 6 (caprylic acid), 8 (capric acid), 10 (lauric acid), 12 (myristic acid), 14 (palmitic acid), and 16 (stearic acid). Oleic acid (CH3-(CH2)7-CH=CH-(CH2)7-COOH) and linoleic acid (CH3-(CH2)4-CH=CH- H2-CH=CH-(CH2)7-COOH) are also common soap ingredients. These sodium salts readily dissolve in water, but other metal ions such as Ca2+ and Mg2+ form precipitates with the fatty acid anions. For example, the dissolution of the sodium salt of lauric acid and the subsequent formation of a precipitate of the lauric acid anion with calcium ion is given by... 

A common form of EDTA used as a preservative is calcium disodium EDTA (CaNa2EDTA). What metals will this form of the sequestrant scavenge effectively The dissolution of the solid will yield calcium ions, sodium ions, and the EDTA anion. Any metal more effectively complexed than calcium will be readily scavenged, including all ions listed in Table 9.1 except silver (Ag+) and magnesium (Mg2+). (In the absence of the calcium counterion, as in the case of the acid form of EDTA, chelation of calcium in the body can occur. In fact, EDTA administered orally is an FDA-approved treatment for calcium deposits in the bloodstream that lead to cardiovascular disease.) Citric acid (Fig. 9.3.3) is another sequestrant of metal ions in foodstuffs. 

Chapter 8 describes a similar one-dimensional chain of identical reservoirs, but one that contains several interacting species. The example illustrated here is the composition of the pore waters in carbonate sediments in which dissolution is occurring as a result of the oxidation of organic matter. I calculate the concentrations of total dissolved carbon and calcium ions and the isotope ratio as functions of depth in the sediments. I present... 

Like the climate system described in Chapter 7, this diagenetic system consists of a chain of identical reservoirs that are coupled only to adjacent reservoirs. Elements of the sleq array are nonzero close to the diagonal only. Unnecessary work can be avoided and computational speed increased by limiting the calculation to the nonzero elements. The climate system, however, has only one dependent variable, temperature, to be calculated in each reservoir. The band of nonzero elements in the sleq array is only three elements wide, corresponding to the connection between temperatures in the reservoir being calculated and in the two adjacent reservoirs. The diagenetic system here contains two dependent variables, total dissolved carbon and calcium ions, in each reservoir. The species are coupled to one another in each reservoir by carbonate dissolution and its dependence on the saturation state. They also are coupled by diffusion to their own concentrations in adjacent reservoirs. The method of solution that I shall develop in this section can be applied to any number of interacting species in a one-dimensional chain of identical reservoirs. 

The reaction rate of sodium acid pyrophosphate can be controlled by adding calcium ions. While this process happens anyway in the presence of skim milk solids, manufacturers deliberately add calcium ions to sodium acid pyrophosphate to give grades with slower dissolution. 

In the presence of fluoride, calcium ions have been found to be more firmly anchored than in pure hydroxyapatite [67]. This enhances the overall resistance to dissolution. Thus, the presence of a thin stable film of fluorapatite on the surface of hydroxyapatite crystals has two effects, namely (i) resistance to diffusion and dissolution of the anion and (ii) firmer binding of calcium ions into the surface. Both of these make the resulting apatite structure more resistant to dissolution, regardless of the pH of the external medium, and they thereby increase the resistance of the mineral phase to the onset of caries. 

Other target organs for the action of 1,25-dihydroxyvitamin D include the kidneys, bone, muscle,vwand skin. The hormone promotes reabsorption of both Ca2+ and inorganic phosphate by kidney tubules. In bone it binds to a specific receptor where it promotes the mobilization of calcium ions. This effect may result in part from stimulation of calcium-activated ATPase of the outer membrane of bone cells. Dissolution of bone also requires the presence of parathyroid hormone (PTH), the 83-residue hormone secreted by the parathyroid gland. In women past the age of menopause and in elderly men the production of 1,25-dihydroxyvitamin D decreases.w This may be a cause of the serious bone loss (osteoporosis) frequently observed. Treatment with 1,25-dihydroxyvitamin D3 or a synthetic analog seems to be helpful to such individuals. /Xy See also Chapter 30, Section A,5. 

Rock salt as well as salt recovered by evaporation of the electrolyte is dissolved at 60 °C, in the mother liquor from the previous operation. Iron tanks provided with stirrers and steam coils arc used for dissolution. Soda is added to the solution to precipitate calcium ions. Otherwise, the calcium ions would... 

Although dissolution in ammonium sulphate may not be complete, calcium ions can be detected in the filtrate with oxalate, after neutralization with ammonia. 

This relationship is true whenever calcium ions and fluoride ions are in equilibrium with calcium fluoride, not just when the salt dissolves. For example, if you mix solutions of calcium nitrate and sodium fluoride, calcium fluoride precipitates. The net ionic equation for this precipitation is the reverse of the dissolution. 

Hydrofluoric acid finds occasional use in conjunction with other acids in attacking steels that dissolve with difficulty in other solvents. Because hydrofluoric acid is extremely toxic, dissolution of samples and evaporation to remove excess reagent should always be carried out in a well-ventilated hood. Hydrofluoric acid causes serious damage and painful injury when brought into contact with the skin. Its effects may not become evident until hours after expo.sure. If the acid comes into contact with the skin, the affected area should be immediately washed with copious quantities of water. Treatment with a dilute solution of calcium ion, which precipitates fluoride ion, may also be of help. 

Fig. 16.6 Hydroxyapatite and fluoroapatite formation and dissolution, (a) Hydroxyapatite is transformed to fluoroapatite by isomorphous replacement. Fluoride ions diffuse into a hydroxyapatite crystal where they replace the hydroxide ions, (b) Fluoroapatite cannot dissolve as easily as hydroxyapatite. Right to left shows the solid-state rearrangement of hydroxyapatite to calcium monohydrogen phosphate, free calcium ions, and monohydrogen phosphate. The latter becomes mostly dihydrogen phosphate above pH 6.2. Arrows between (b) and (a) indicate enhanced apatite formation or slower changes to the amorphous solid if fluoride is present. Left to right shows the precipitation of calcium monohydrogen phosphate and its change to hydroxyapatite if an acid solution is made alkaline.

Soap scum is an insoluble precipitate that forms between the cations of minerals typically present in hard water and the anions of soaps and detergents. Divalent cations of calcium (Ca2+) and magnesium (Mg2+) from calcium carbonate and magnesium carbonate minerals are the primary components of hard water. Divalent cations of iron (Fe2+), manganese (Mn2+), and strontium (Sr2+) are also often present. An example of the dissolution (dissolving) process that releases calcium ions from calcium-containing minerals in contact with water with high acid levels is... 

PHEMA into an SBF solution. At the higher released citric acid concentrations, the formation of calcium citrate crystals can bring about a depletion of the calcium ion concentration in the SBF solution, so less calcium phosphate will precipitate onto the polymer. At lower citric acid concentrations, the inhibition effect of citrate anions on formation of calcium phosphates has been attributed to the complex equilibria between calcium, citrate and phosphate ions (27-29). Precipitated calcium phosphates may undergo dissolution via surface exchange between phosphate and citrate ions (calcium citrate is much more soluble than calcium phosphate). 

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