Determination of Tungsten Trioxide Contained in Sodium Tungstate

The method for the determination of tungsten trioxide in tungstic acid is mainly based on the weight method of cinchonine. The principle is that the tungstic acid is separated from the impurities by using cinchonine hydrochloride in a hydrothermal solution with pH value of 3.00-4.4, And then burning it to get the product of tungsten trioxide, the final weighing, colorimetric to determine the content of tungsten trioxide.

Sodium tungstate content of tungsten trioxide used in the determination of reagents used are: methyl violet indicator 0.1%, hydrochloric acid (1 +1), 10% of cinchonine hydrochloride solution (prepared with 1 +1 hydrochloric acid), 0.2 of cinchonine hydrochloride 0.2 %, solid NaOH and extensive test strips.

The determination of the content of tungsten trioxide in tungstic acid is as follows:

 1. Weigh 0.5 g of the sample in a 250 ml beaker and dissolve with a little water. Add 100ml of hot water at 60 ~ 80 ℃, 2 drops of 0.1% methyl orange finger (if the indicator brown added) with hydrochloric acid (1 + 1) to red.
2. Add 10% cinchonine 10ml with constant stirring, continue stirring to precipitate coagulation, the supernatant clearer than the rest. After sedimentation sink, with fast quantitative filter paper, the filtrate to take in 250ml volumetric flask. Sediment washed with 0.2% simplistic lotion more than five times, after washing the precipitate with the filter paper into porcelain crucible. On the electric oven drying charring, and then charcoal furnace at 750 ~ 800 ℃ burning 30 to 45 minutes, cooled and weighed. The filtrate was tannin methyl violet colorimetric method.

Analysis of the results of the calculation: WO₃ (%) = (W / G) × 100 + C. Where: W - tungsten trioxide weight (g), G - weighed sample weight (g), C - measured WO₃ content in the filtrate.

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