Acid Hydrochloric Molybdic

The acids used in the methods are nitric, sulfuric acid, hydrochloric acid, and perchloric acid. If the acid concentration is very low, other precipitation may predominate, and if the concentration is too high, the color will be faint or ultimately obsolete. A maximum is reported to be at approximately pH 1.5. Even though the vanadate/molybdate concentration may vary a lot, vanadate should always be in excess to the analyt. In older publications vanadate and molybdate are added separately and in this case they should be added in the order add, vanadate, and molybdate. Changing this apparently can lead to other precipitations or complexes. 

Procedure. Spot test paper (Mackeray, Nagel Co. No. 640 W) is used. One drop of 0.1% alcoholic solution of o-hydrox5q>henylfluorone is applied and dried at room temperature. The orange fleck is spotted with one drop of the 2 N hydrochloric acid test solution and then with a drop of 20 % potassium fluoride solution followed by 2 or 3 drops of 0.5 N sulfuric acid. If molybdate is present a carmine fleck results. When dealing with slight amounts of molybdate it is best to conduct a blank. 

The method may be standardised, if desired, with pure potassium dihydrogen-orthophosphate (see below) sufficient 1 1 hydrochloric acid must be present to prevent precipitation of quinoline molybdate the molybdophosphate complex is readily formed at a concentration of 20 mL of concentrated hydrochloric acid per 100 mL of solution especially when warm, and precipitation of the quinoline salt should take place slowly from boiling solution. A blank determination should always be made it is mostly due to silica. 

Discussion. Molybdates [Mo(VI)] are quantitatively reduced in 2M hydrochloric acid solution at 60-80 °C by the silver reductor to Mo(V). The reduced molybdenum solution is sufficiently stable over short periods of time in air to be titrated with standard cerium(IV) sulphate solution using ferroin or /V-phenylanthranilic acid as indicator. Nitric acid must be completely absent the presence of a little phosphoric(V) acid during the reduction of the molybdenum(VI) is not harmful and, indeed, appears to increase the rapidity of the subsequent oxidation with cerium(IV) sulphate. Elements such as iron, copper, and vanadium interfere nitrate interferes, since its reduction is catalysed by the presence of molybdates. 

In the preparation of a dyestuff from aniline, nitrobenzene (as oxidant), hydrochloric acid and sodium hydroxide, ferric chloride is often used as catalyst, but sodium molybdate was substituted as a more effective catalyst. The materials were charged into a 4.5 m3 reactor and heating was started after addition of nitrobenzene, but the temperature controller was mis-set, and overheating at a high rate ensued. The exotherm was much higher than normal because of the more effective catalyst, and partial failure of the cooling water led to an uncontrollable exotherm. 

The pigments are obtained by preparing an aqueous solution of disodium hydrogenphosphate and adding a sodium molybdate solution (containing molybdenum trioxide and aqueous sodium hydroxide). Acidified with hydrochloric acid or with sulfuric acid, the reaction mixture is then added to an aqueous solution of the... 

The chromatographic separation of technetium from molybdenum is based on the different extent to which molybdate and pertechnetate are adsorbed from alkaline and acid solutions. The distribution coefficient of molybdate between the anion exchanger Dowex 1-X8 and 3 M NaOH is 12, while it is 10 for pertechnetate under the same conditions. Molybdate is also adsorbed to a much lesser extent from hydrochloric acid solutions than pertechnetate. Thus, molybdemun can be eluted by hydroxide or HCl solutions while nitric acid, perchlorate or thiocyanate are used for the elution of technetium . 

Pour 2-3 ml of a 10 % nitric acid solution into 2-3 ml of a 20 % ammonium molybdate solution. What substance precipitates What is its colour Wash the precipitate with water by decantation and divide it into two parts. React one part of the precipitate with an excess of concentrated hydrochloric acid and the other with a 20% sodium hydroxide solution. Explain the results. Write the equations of the reactions. Under what conditions does molybde-num(Vl) oxide dihydrate form ... 

Reduction of MoIybdenum(VI) and Tungsten VI) Compounds. Pour 3 ml of an ammonium molybdate solution into each of four test tubes, acidify with a 2 N hydrochloric acid solution, and heat up to boiling. Add solutions of sulphuric acid, hydrogen sulphide, and tin(Il) chloride to three of the tubes, respectively, and throw one or two small pieces of zinc into the last tube. Perform similar experiments using sodium tungstate as the initial reactant. Write the equations of the reactions. 

Preparation of Potassium Hexachloromolybdate(III). Perform the experiment in a fume cupboard ) Dissolve 50 g of molybdic anhydride in 250 ml of concentrated hydrochloric acid. Spill the molyb-denum(Vl) oxide into the beaker in small portions as it dissolves during 6 hours. If the solution is turbid, filter it through a glass filter (prepare the solution beforehand). 

Phosphates Ammonium molybdate solution made from 3 g of ammonium molybdate in 20 m/ of perchloric acid (40%) and 5 ml of concentrated hydrochloric acid in 200 m/ of water ( 10 min 100°C) subsequently saturated hydrazine sulphate solution (20 min 110°C)... 

Fifty grams t of sodium molybdate is dissolved in 200 ml. of water, and the solution heated to 60°C. To this solution is added 20 ml. of concentrated hydrochloric acid (density 1.18). The mixture is stirred vigorously with a... 

In the preparation of a dyestuff from aniline, nitrobenzene (as oxidant), hydrochloric acid and sodium hydroxide, ferric chloride is often used as catalyst, but sodium molybdate was substituted as a more effective catalyst. The materials were charged... 

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