Quantitative Chemical Analysis (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ...at 130 to constant weight, and calculate the chloride as hydrogen chloride. EXERCISE XIV. Determination ofPko_centshoric Acid. (a) By Precipitation as Phosphomolybdate.--Prepare a concentrated solution of ammonium nitrate. Prepare also a molybdate solution as follows: Dissolve 37.5 gms. of ammonium molybdate in 250 cc. of water to which a little ammonia is added. Filter if turbid. Make a mixture of 12 5 cc. each of concentrated nitric acid and water, and while constantly stirring, pour the solution of ammonium molybdate into it. Set the solution aside in a warm place for a few days and then filter before use. Heat the phosphate solution given you nearly to boiling and, while constantly stirring, add 50 cc. of molybdate solution. Stir for a while, maintaining the temperature on a water bath for about ten minutes. Allow the mixture to stand for an hour; then, filter through a Gooch crucible. Test the filtrate for the presence of phosphoric acid by the addition of molybdate solution; if present, return the precipitate to the crucible. Wash the precipitate thoroughly with a solution containing 50 gms. of potassium nitrate and 40 cc. of concentrated nitric acid per liter. Place the Gooch crucible inside of a larger crucible. and heat gently until there is no further evolution of ammonia; then ignite, cool, and weigh as phosphomolybdic anhydride. Report the amount of P, O5 in the portion of solution given you. " (b) Precipitation as Ammonium-Magnesium Phosphate.--The phosphate may be at once precipitated by magnesia mixture (see determination of magnesium), or, the phosphomolybdic precipitate may be redissolved and precipitated by magnesia mixture. If the latter method is employed, after washing _the molybdate precipitate a beaker is placed under the funnel