Tungstic tungstate

Tungstic Tungstate, or the blue oxide of tungsten, is described on p. 200. 

Ammonium tungstate [11140-77-5] (NH 2 0cannot be obtained from an aqueous solution because it decomposes when such a solution is concentrated. It is prepared by the addition of hydrated tungstic acid to Hquid ammonia. 

Polytungsta.tes, An important and characteristic feature of the tungstate ion is its abiUty to form condensed complex ions of isopolytungstates in acid solution (38). As the acidity increases, the molecular weight of the isopolyanions increases until tungstic acid precipitates. However, the extensive investigations on these systems have been hampered by lack of weU-defined soHd derivatives. 

Ammonium tungstate (VI) [11120-25-5] M 283.9, pK] 2.20, pK2 3.70 (for tungstic acid, H2WO4). Crystd from warm water by adding EtOH and cooling. 

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

The series of deviation from a strictly octahedral crystal field follows the sequence ammonium tungstate > tungstic acid > WO3 [14]. The s->d transition becomes allowed as distortion of the octahedral environment increases. Viewed as a fingerprint technique. Figure 6 shows that the bulk of W present in both WZ (calcined) and PtWZ(acac, reduced) behaves as WO3, as also shown by our XRD data [10], sugesting that only a small extent of W reduction is expected to have taken place during catalyst conditioning prior to reaction. 

Tungstic acid Sodium tungstate 10 g 1 , sulphuric acid 0.05 mol 1 1... 

When this dissolved form of WO3 is acidified, tungstate ion is converted to the metastable tungstic acid, which slowly reverts back to WO3 and water ... 

Sodium tungstate is crystallized, separated from any impurities in the solution, and digested again with hydrochloric acid to form tungstic acid in purified form. The pure acid is dried, ignited and reduced with carbon to form tungsten powder from which most non-ferrous alloys are made. 

Tungstic acid is obtained as an intermediate in the recovery of tungsten from its minerals, scheebte and wolframite (See Tungsten). Also, the tungstic acid may be prepared by heating sodium tungstate with sulfuric acid or hydrochloric acid ... 

Proteins from tissue homogenates are precipitated by tungstic acid. Mix homogenates, which contain about 1% protein, with 1/10 of volume of 10% sodium tungstate (Na2W04 H2O) (w/v), and acidify with the same volume of 0.67 N sulfuric acid. Collect the precipitate after 10 min at RT by centrifugation. Nucleic acids are precipitated by tungstic acid to a minor extent. 

Sodium tungstate dihydrate Tungstic acid, disodium salt, dihydrate (10213-10-2), 65, 166... 

Molybdic and Tungstic Anhydrides. Place several ammonium molybdate crystals onto the lid of a crucible and first heat them carefully, and then roast them strongly. What occurs Perform a similar experiment with ammonium tungstate or tungstic acid. Write the equations of the reactions. At what temperature do molybdic and tungstic anhydrides sublime ... 

Salts of Molybdic and Tungstic Acids. What types of salts of molybdic and tungstic acids exist Give examples of isopoly- and heteropoly molybdenum and tungsten compounds. What is the composition of para- and metamolybdates and of para- and metatungstates Which molybdates and tungstates dissolve poorly in water ... 

Preparation of Normal Ammonium Tungstate. Weigh 0.5 g of tungstic acid in a test tube, put the latter into a cooling mixture (solid carbon dioxide with acetone), and pour in 1-2 ml of liquid ammonia. Stir the contents of the test tube with a cooled glass rod and let the ammonia evaporate. Examine the precipitated crystals under a microscope. What is the composition of the product ... 

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