12-Molybdosilicic acid

Molybdenyl acetylacetonate, 6 147 12-Molybdosilicic acid, 1 127 analysis of, 1 128 Monazite, extraction of, 2 38 separation of rare earths from, 2 56... 

Similar insoluble salts form with many cationic chelates of heavy metal atoms. Thus, 12-molybdosilicic acid precipitates Cu+2, Ag+, Cd+2, Zn+2, Sn+2, Cr+3, Ni+2, and Co+2 in the presence of ethylenediamine, thiourea, hexamethylenetetramine, dithiooxamide, or similar chelating agents 106 ... 

The solubility of 12-molybdophosphoric and 12-molybdosilicic acids and several transition metal salts has been determined5 in various solvents and is given in Table 8. 

Most free acids of 12-heteropoly anions of Series A form isomorphous 30-hydrates. These melt in their own water of hydration at 40 to 100 °C. They begin to lose water in dry air and give up almost all 30 molecules in vacuum over sulfuric acid. The transition metal salts of the 12-molybdophosphoric and 12-molybdosilicic acids lose water up to 300 °C5 The hydrated free acids may be converted to the anhydrous H3[PMoi204o] and H4[SiMo1204o] by heating at 180 °C, the products thus obtained can be rehydrated at room temperature5. The hydrated acids... 

Meaningful thermal stability studies on heteropoly compounds must be accompanied by solubility studies of the heated materials to ascertain actual decomposition. In addition, the length of heating must also be specified since such decomposition may be rate dependent in view of the fact that both 12-molybdophosphoric and 12-molybdosilicic acids decompose slowly with time even at room temperature5. ... 

The 12-molybdosilicic acid and the corresponding titanium and zirconium 12-acids may be neutralized intact by 4 KOH. Degradation begins only on further treatment with KOH at about pH 4.5 for the Ti and Zr complexes and even then... 

The thermal decomposition of alpha-12-molybdosilicic acid, H SiMo O ] and its two and four electron reduction products, H6[SiMo12040] and H8[SiMoi204o] has been studied in detail173-177). The reduced products decompose at higher temperatures than the oxidized species, the oxides of molybdenum that result from such decomposition have surface areas 10 m2/g. The reduced product yield Mo4Ou upon decomposition. 

Molybdosilicic Acid, Hg[Si(Mo20,)j].28H,0, is prepared by decomposing the sodium salt vith dilute sulj huric acid and e.xtraeting wdth ether. It yields transparent octahedral which melt at 47° to 55° C. to a uniform liquid. Crystallised from hot nitric acid it yields a lower hydrate with I4H2O. 

H4SiMoi2O40-a H2O Silicomolybdic acid H4Si04l2Mo0r- rHjO 12-Molybdosilicic acid... 

After converting silica to alpha-12 molybdosilicic acid, the latter can be titrated with ferrous sulfate in the presence of EDTA, tartaric acid, and chloroacetic acid buffer at pH 2.5, The end point is determined amperometrically with two platinum electrodes (332). 

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