Magnesium oxalate

Glyoxylic acid solution (protein detection) cover 10 g of magnesium powder with water and slowly add 250 mL of a saturated oxalic solution, keeping the mixture cool filter off the magnesium oxalate, acidify the filtrate with acetic acid and make up to a liter with water. 

Appreciable errors may also be introduced by post-precipitation. This is the precipitation which occurs on the surface of the first precipitate after its formation. It occurs with sparingly soluble substances which form supersaturated solutions they usually have an ion in common with the primary precipitate. Thus in the precipitation of calcium as oxalate in the presence of magnesium, magnesium oxalate separates out gradually upon the calcium oxalate the longer the precipitate is allowed to stand in contact with the solution, the greater is the error due to this cause. A similar effect is observed in the precipitation of copper or mercury(II) sulphide in 0.3M hydrochloric acid in the presence of zinc ions zinc sulphide is slowly post-precipitated. 

The rate equation [eqn. (26)], given above for the reaction of magnesium oxalate, is also obeyed [1012] by the decomposition of zinc oxalate (620—646 K), although here the catalytic (second) term is dominant, so that behaviour approximated to the Prout—Tompkins equation [eqn. (9)]. The value of E (201 8 kJ mole 1) was the same as that found... 

Post-precipitation involves the deposition of a sparingly soluble impurity of similar properties to the precipitate on the surface of that precipitate after it has been formed. It is particularly a problem where similar materials are being separated on the basis of their different rates of precipitation, e.g. calcium and magnesium oxalates or zinc and mercury sulphides. Copreci-... 

BIOCHEMICAL THERMODYNAMICS Magnesium oxalate dihydrate (MgC204-2H20),... 

Magnesium Oxalate. MgCsOq - 2HiO, white solid, insoluble. K r 8.6 x It) formed by reaction of soluble magnesium salt solution and ammonium oxalate solution. 

Water is hard if it contains high concentrations of calcium and magnesium ions, Ca2+ and Mg2+. If these ions are present in lower concentrations, the water is considered to be soft. Distilled water has few ions of any kind, and no Ca2+ or Mg2+. Sodium oxalate, Na2C204, is a compound that causes Ca2+ to precipitate as calcium oxalate, CaC204, and Mg2+ to precipitate as magnesium oxalate, MgC204. 

Some precipitates are deposited slowly and the solution is in the state of supersaturation for a considerable time. Thus, when calcium oxalate is precipitated in the presence of larger amounts of magnesium ions, the precipitate is practically pure at first, but if it is allowed to remain in contact with the solution, magnesium oxalate forms slowly (and the presence of calcium oxalate precipitate tends to accelerate this process). Thus, the calcium oxalate precipitate becomes contaminated owing to post-precipitation of magnesium oxalate. Post-precipitation often occurs with sparingly soluble substances which tend to form supersaturated solutions, they usually have an ion in common with the primary precipitate. Another typical example is the precipitation of copper or mercury(II) sulphide in dilute acid solution, which become contaminated, if zinc ions are present, by post-precipitation of zinc sulphide. Zinc ions alone may not be precipitated with sulphide ions under identical circumstances. 

Mikhail et al. (1971) obtained a series of porous products by the thermal decomposition of magnesium oxalate dihydrate in vacuo at temperatures in the range 400-600°C. The BET areas derived from the adsorption isotherms of nitrogen and cyclohexane are given in Table 10.14. The values of ct(N2) and ct(C4H4) have been taken as 0.162 nm2 and 0.39 nm2, respectively. 

Postprecipitation Postprecipitation involves the formation of a second insoluble substance on a precipitate already formed, as a result of differences in rates of precipitation. For example, in the separation of calcium from magnesium by oxalate precipitation of calcium, the solubility of magnesium oxalate may be exceeded. But, since magnesium oxalate has a pronounced tendency to remain in supersaturated solution, it slowly precipitates on the caldiun oxalate over a period of many hours. 

Oxalic acid and its soluble salts are poisonous to humans and animals, whereas insoluble salts of calcium and magnesium oxalate are not. Oxalates ingested by humans may be precipitated by calcium as an insoluble complex, which then is excreted in feces [21, 22, 23]. In both cases reported by Chien et al [21], patients ingested sour carambola juice on an empty stomach so that the protective effect of calcium and magnesium in food was not present. The dehydration state may have contributed to the development of carambola- associated acute nephropathy. The authors do not report any concomitant neurological signs or symptoms [21]. 

Similarities were found between the patterns of behaviour reported for the zinc and magnesium oxalates. The stoichiometry of decomposition of magnesium oxalate (claimed to be accurate to 1%) (623 to 773 K) is [76] ... 

The initial acceleratory stage a < 0.3) was attributed primarily to the growth of nuclei formed during removal of water from the dihydrate, and it was suggested that similar elementary processes operate during the decay period. Kinetic observations [75] for the isothermal decomposition of magnesium oxalate (603 to 633 K) were represented by the two term rate equation ... 

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