Magnesium indications

Notes. (1) The usefulness of the HHSNNA indicator for the titration of calcium depends upon the fact that the pH of the solution is sufficiently high to ensure the quantitative precipitation of the magnesium as hydroxide and that calcium forms a more stable complex with EDTA than does magnesium. The EDTA does not react with magnesium [present as Mg(OH)2] until all the free calcium and the calcium-indicator complex have been complexed by the EDTA. If the indicator is added before the potassium hydroxide, a satisfactory end-point is not obtained because magnesium salts form a lake with the indicator as the pH increases and the magnesium indicator-lake is co-precipitated with the magnesium hydroxide. 

Detailed analysis of the perimeter residue often yields useful information, for example, whether the bullet is unjacketed or jacketed and the nature of the jacket material. Primer type may occasionally be inferred and the presence of strontium or magnesium indicates a tracer or incendiary bullet, respectively. 

The magnesium-indicator complex is more stable than the calcium-indicator complex but less stable than Magnesium-EDTA complex. 

Consequently, during titration of solution containing magnesium and calcium ions with EDTA in presence of Eriochrome Black T the EDTA first reacts with the free calcium ions, then with the free magnesium ions, and finally with the magnesium-indicator complex. Since magnesium-indicator complex is wine red in colour and the free indicator is blue between pH = 7-11, the colour of the solution changes from wine red to blue at the end-point. 

Fig. 13.11 The concentrations of nickel and copper in the Vanda hypersthene sill vary stratigraphically in the opposite sense. The mafic zone of this sill is strongly enriched in nickel and depleted in copper, whereas the felsic zone is enriched in copper and depleted in nickel. The lowest concentrations of nickel and the highest concentrations of copper occur in the layer of pegmatoid at 270 m above the base of the sill. Nickel is closely correlated to magnesium indicating that it resides in pyroxenes, whereas copper and zinc probably occur as sulfides in these rocks (Data from Gunn 1966)...

Both adsorbing colloid and precipitate flotation have been studied in laiger columns. Results for lead, copper, chromium, and magnesium indicate drinking level residuals are possible after treatment at optimum conditions. The operating conditions and results for several studies are provided in Table 17.5-1. 

Biological Applications Copper indicator calcium indicator cadmium indicator iron (II) indicator iron (III) indicator fluoride indicator lanthanides indicator magnesium indicator silver indicator sulfate indicator zinc indicator treating atherosclerosis, restenosis, hypertension ... 

Biological Applications Magnesium indicator calcium indicator zinc indicator ... 

The values of AH indicate that it is extremely unlikely that MgCljIs) can be prepared under any conditions, but both MgCl(s) and MgCl2(s) appear to be energetically stable with respect to magnesium and chlorine. 

Ether solution (E,). This will contain any neutral compounds present. Dry with anhydrous magnesium sulphate, and distil ofi the ether. A residue indicates the presence of a neutral component. Determine the solubility of a portion in cone. HjS04. Apply any other suitable tests. 

BackTitrations. In the performance of aback titration, a known, but excess quantity of EDTA or other chelon is added, the pH is now properly adjusted, and the excess of the chelon is titrated with a suitable standard metal salt solution. Back titration procedures are especially useful when the metal ion to be determined cannot be kept in solution under the titration conditions or where the reaction of the metal ion with the chelon occurs too slowly to permit a direct titration, as in the titration of chromium(III) with EDTA. Back titration procedures sometimes permit a metal ion to be determined by the use of a metal indicator that is blocked by that ion in a direct titration. Eor example, nickel, cobalt, or aluminum form such stable complexes with Eriochrome Black T that the direct titration would fail. However, if an excess of EDTA is added before the indicator, no blocking occurs in the back titration with a magnesium or zinc salt solution. These metal ion titrants are chosen because they form EDTA complexes of relatively low stability, thereby avoiding the possible titration of EDTA bound by the sample metal ion. 

Table 8 indicates the compatibiUty of magnesium with a variety of chemicals and common substances. Because the presence of even small amounts of impurities in a chemical substance may result in significantly altered performance, a positive response in the table only means that tests under the actual service conditions are warranted (132). Other factors which may significantly alter magnesium compatibiUty include the presence of galvanic couples, variations in operating temperatures, alloy composition, or humidity levels. 

Some tests indicate that magnesium alloys are resistant to loam sod. However, in the presence of chlorides, corrosive attack may be serious particularly if galvanic couples are present as a result of coupling to iron stmctures. 

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