A N A L Y T I C A L CHEMISTRY
410 alternative procedures. The character and reasons for the specificity of this precipitation have been examined. ACKNOWLEDGMENT
The authors are indebted to Wilfred Byrd and Goji Kodama for the microanalyses. LITERATURE CITED
(1) Berg, R., and Wurm, O., Ber., 60, 1664 (1927); 98,287 (1934). (2) Flagg, J. F., “Organic Reagents,” Kew York, Interscience Publishers, 1948. (3) Furman, N. €I., “Scott’s Standard Methods of Chemical Analysis,” New York, D. Van Iiostrand Co., 1939. (4) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganir .4nalysis,” New York. John Wiley & Sons, 1929.
(5) Kolthoff, I. AI,, arid Lingane, J. J . , “Polarography,” 1-01. I.
New Tork, Interscience Publishers, 1952. (6) Mahr, C . , Z. anorg. u . allgem. Chem., 225, 386 (1935). (7) Mahr, C.. and Ohle, H., Z. anal. Chen., 109, 1 (1937). (8) hlahr, C., and Ohle, H., 2. anorg. u . allgem. Chem., 234, 224 (1937). (9) Prodinger, W., “Organic Reagents Used in Quantitative In-
organic Analysis,” Sew York, Elsevier Publishing Co., 1940. (10) Redlich, O., et al., J . .4m.Chenf.Soc., 72, 4153, 4161 (1950). (11) Rulfs, C. L., Anal. Chim. A c t n , 5,46 (1951). (12) Schiessler, R. W., and E‘litter. D., J . dm. Chem. Soc., 74, 1720 (13) (14) (15) (16)
(1952). Ytrebinger, R., and Ortner. G., Z. a m l . Chem., 107, 14 (1936). Thompson, T. L., I m . E x ; . CHEM., A x . 4 ~ED., . 13, 164 (1941). ~ ~ ~24,~984 . (1952). Walter, J. L., and Freiser, H., A 4 CHEM., Welcher, F. J., “Organic Analytical Reagents,” Iiew Y o r k , D. Van Sostrand Co., 1947.
RECEITED for review September 25, 1952.
Accepted September 19, 1953.
Reduction by Aluminum Powder in Aqueous Solution Titrimetric Determination of Molybdenum E. RAYMOND RIEGEL’ and ROBERT D. SCHWARTZ’ University o f Buffdfalo, BuffaTo, N. Y.
S
EVERAL reducing agents have been proposed for use in the titrimetric determination of molybdenum (1,S, 7,9, 10). Although Willard and Furman (10) list the action of aluminum on molybdenum(V1) in acid solution, no journal reference t o this reaction was located. Boulanger’s ( 2 ) work, in alkaline solution, was the only reference to the reduction of molybdenum(V1) by aluminum. PRELIMINARY STUDIES
A sample of
C.P. ammonium molybdate was used as the source
of molybdenum(V1) for this work. This material was assayed by the method of Birnbaum and Walden (1). The Moo3 contcnt was 81.0%. The first reductions were performed in 2111 hydrochloric acid solution. Alcoa (99.4%) aluminum foil was used as the reducing agent. As the mixtures were heated, the colorless molybdcnum(VI) solutions became orange and then green. The green solutions became orange if they were exposed to air. From the information given by Hiskey (4), it was possible to decside that the orange solutions contained molybdenum(V), and that the green solutions were molybdenum(IT1) materials. These results confirmed the data given by Willard and Furman (IO). I n order to determine whether the reduction could be carried past the (111) state, samples were reduced in an atmosphere of nitrogen by a large excess of aluminum. N o color change after the green (111) state was observed. The reaction between aluminum foil and molybdenum(V1) in hydrochloric acid solution leads to the formation of molybdenum(II1). Molybdenum(\‘) was the only intermediate in the reduction and in the air oxidation of molybdenum(II1). The nonexistence of molybdenum(1V) was confirmed by POtentiometric studies of the reaction. Time-potential curves were plotted during the reduction using platinum-calomel electrodes and a Beckman Model G pH meter. Additional confirmation was obtained by potentiometric measurements made during the oxidation of molybdenum(III), in 2J1 hydrochloric acid, by ceric sulfate. Sidgwick (8) indicates that molybdenum(1V) exists only as certain complexes. Other molybdenum(1V) compounds are unstable in aqueous solution by virtue of reaction to givc a mixture of molybdenum(II1) and molybdenum(V). REDUCTION USING FINE ALUMIh-U>.I POWDER
A fine aluminum powder (Reynolds No. 400) was found advantageous by the authors (6) for iron determinations. Samples of molybdenum(V1) in 1.25-21 sulfuric acid were Present address, R . D. 91, Deep River, Conn. Present address, Exploration and Production Research Laboratory, Shell Development Co., Houston, Tex. 1
2
heated with No. 400 aluminum powder in an atmosphere of nitrogen. As in the reduction of iron(II1) ( 6 ) , the powder yielded more rapid reaction and hetter efficiency of reduction than foil. -Uter reduction the samples werp allowed to coel in the nitrogen atmosphere. Titration with potassium permanganate yielded molybdenum(F‘1). However, st room temperature the oxidation of molybdenum( V) by permanganate waa slow. Potential measurements] taken during the titration, revealed that upon each addition of permanganate the potential rose sharply, and then dropped slowly as the oxidant reacted with molybdenum-
(V). Other samples were reduced with S o . 400 powder and were titrated with potassium permanganate while warm. A t the elevated temperatures the reaction was rapid and good end points were obtained. Several samples of molybdenuni(V1) in 1.25‘51 sulfuric acid were reduced with an exrcss of S o . 400 powder and titrated with permanganate. The results obtained were compared with those yielded by the procedure of Birnbaum and Walden ( 1 ) . Molybdenum
Sulfuric Acid, Moles p?r Liter 1 .2A I .25 1.26 1. 2 5 Silvrr Silver Silver Silvrr
(VI)
Taken, hleq. 0 . zoo 0.750 1.010 1.500 0 . zoo 0.760 1.000 2.150
Aluminum,
Molybdemini ( V I ) Found, hleq.
Meq.
?.??
0.490 0.740 1.012 1.448 0.499 0.752 1,003 2.144
0 ,O D
11.1 11.1 Reductor Reductor Reductor Reductor
The agreement with results obtained by the silver reductor procedure ( 1 ) was satisfactory. XIETHOD OF DETERWINING MOLYBDENUM
Samples of C.P. ammonium molybdate were analyzed for molybdenum by the silver reductor procedure, the Jones reductor procedure, and by the use of Reynolds No. 400 aluminum powder as the reducing agent. The results obtained are listed below.
Sample
Silver reductor
1
81.0
2
80.7
81.03 81.09 80.74 80.71
hIOOl, % Jones reduetor 81.1 80.8
81.12 81 .OS 80.83 80.78
Aluminum 81.1 80.7
81.16 81.11 80.73 80.67
V O L U M E 26, NO. 2, F E B R U A R Y 1 9 5 4
411
The method of analysis using aluminum powder was more rapid and required fewer reagents and less equipment than the reductor procedures.
interfere with reduction by aluminum. They would have to be removed prior to reduction or corrected for by a determination using some other method.
PROCEDURE FOR A S S A Y O F AMMONIUM MOLYBDATE
4(:h?OWLEUC:hlENT
A weight of sample chosen to yield from 1 to 2 meq. of molybdenum was transferred to a 125-ml. Erlenmeyer flask and dissolved in 25 ml. of water. Then 14 meq. of No. 400 aluminum povder were added. The sides of the flask were washed down with 25 ml. of 2.50M sulfuric acid. A supply of nitrogen was passed into the flask through a tapered glass tube. The sample was then heated on a small electric hot plate turned to low heat. After the aluminum had dissolved, the sample was heated for 5 more minutes with nitrogen bubbling through the mixture. Then the sample was removed from the hot plate and was immediately titrated with standardized potassium permanganate solution. The nitrogen stream was kept on during the titration and provided the necessary stirring. DISCUSSION
The silver reductor procedure ( 1 ) for the determination of niolvbdenum is somewhat inconvenient, since i t is necessary to preheat the sample, the reductor, and the wash solutions. The Jones reductor procedure (3) is more convenient, but requires the use of iron(II1) alum solution. Rahm (5) haq rcwntly mrntioned some of the disadvantag6q inherent in t h r use of the Jones reductor. The use of finelv divided aluminum powder as the reducing agent requires the use of an inrrt atmosphere to prevent oxidation of molybdenum(II1) by air. This was acromplished by passing nitrogen gas from a cylinder into the Erlenmeyer flask used for the reduction and titration. T h r nitrogen also provided thr necessary stirring. .4ny substances that arc reducible with the Jones ieductor
The authors wish to thank the ,%luminum Co. of America for providing samples of foil, and thc Reynolds Metals Co. for providing samples of powder. LITERATURE CITED
( I ) Rirnbaum, N., and Walden, G. H., Jr., J. Am. Chem. Soc., 60, 64 (1938). (2) Boulanger, C., Compt. rend., 191, 56 (1930). (3) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 249, New York, John Wiley & Sons, 1929. (4) Hiskey, C. F., J . A m . Chem. Sac., 61, 3125 (1939). (5) Rahm, J. A , , ANAL.CHEM.,24, 1832 (1952). (6) Riepel, E. R . , and Schwarta, R. D., Ibid., 24, 1803 (1952). (7) Furman, li. €I., “Scott’s Standard Methods of Chemical Analysis,” 5th ed., Vol. I, p. 593, New York, D. Van S o s trand Co., 1939. ( 8 ) Sidgwick, N. V., “The Chemical Elements and Their Compounds,” Vol. I, p. 1055, London, Oxford University Press, 1950. (9) Willard, H. H., and Diehl, €I., “Advanced Quantitative Analysis,’’p. 227, Kew Tork, D. Yan Nostrand Co., 1943. (10) Willard, H. H., and Furman. S . H., “Elementary Quantitative Aiialysis,” 3rd rd., 1). 203, Yew York, D. Van Nostrand Co., 1940. RECEIVED for review May 2 , l958.
Accei>ted September 29, 1QZ3. PEwnted before the Division of Analyticul Cheinistry a t the 123rd Meeting of the AYEHICANCHEMICAL SocxE,rY, Lo.? Angdes, Calif., 1953. Taken in part from a thesis submitted by I?. D . Schwarta t o the Graduate School of the University of Buffalo in partial inlfill~nrntof the requirements for the df-grre of doctor of philosophy.
Spectrophotometric Determination of Sodium Hypophosphite as a Molybdenum Blue Complex ANTHONY P. SCANZILLO Thomson Laboratory, General Electric Co., Lynn, Mass.
T
HEIU are only a few quaiititative chemical mcthods for drtermining sodium hypophosphitc or hypophosphorous acid. In the gravimetric methods, hypophosphorous acid is converted into phosphoric acid by adding nitric acid to an aqueous solution, evaporating to a small volume, and completing the oxidation according to Treadwell and Hall (9) or according to the Xnierican Society for Testing Materials method ( 1 ) . The phosphoric acid or phosphate may then be deterininrd hy conventional methods ( 4 , 11). In the volumetric detrrmiiiation, hypophosphorus acid and hypophosphites are oxidized with potassium permanganate (5) or bromide-bromate solution (4).anti thr rscess is determined iodometrically. Treadwell and Hall (IO) include a procedure for dctcrmining phosphorous and hypophosphorous acids in mistures by an indirect analysis. One portion of the samplc is osidized to phosphoric acid, and the phosphate is drtermined as magnesium pyrophosphate. A second portion is treated with mercuric chloride. and the mercurous chloride formed is neighed. From these data the amount of each acid present may be determined by use of simultaneous equations. In this laboratory, however, the results wrre very low when the mercuric chloride method was used on solutions containing known amounts of sodium hypophosphite. It is possible that some of the mercuric chloride is reduced to metallic mercury (8). The method developed is simple and applicable in the presence of sodium phosphitp. According t o Millard (6, 7), hypophos-
phorous acid or hypophosphites give a blue coloratiori 151th ammonium molybdate and sulfurous acid. Ebaugh and Smith (3, 6) claimed that molybdic ncid is reduced t o the pentoside and that the method is not reliable for quantitative mark. However, it KRS found that thc color produced obeys Beer’s I:rn METHOD
Reagents. Ammonium lirpta molybdate, loyo. Dissolve 100 grams of C.P. ammonium molyldate in 600 ml. of hot water Digest on 3, steam bath, cool, and dilute to 1 liter with distilled water. Sulfurous Acid, assay 6% sulfur dioxide by volume. Merck’s reagent grade gave the lowest blank and most consistent result*. Apparatus. Transmittancy measurements were made with a Coleman Model 14 Universal spectrophotometer, using matc~hed round cuvettes, 19 mm. in diameter. Procedure. For solutions of high concentration, take an a-ml. aliquot containing not more than 0.5 gram of sodium hypophosphite (NaH2P02.H20) and dilute to 1000 ml. in a volumetric flask and mix well. Transfer a b-ml. aliquot containing not more than 2.5 mg. of sodium hypophosphite to a 100-ml. volumetric flask and add water t o bring the volume t o 10 ml. Add 10 ml. of ammonium molybdate solution and 10 ml. of sulfurous acid and heat in a boiling water bath for 3 minutes. Let stand a t room temperature for 1 minute, then cool immediatelv in running water. Prepare a blank by taking 10 ml. of distilled water through the same steps as the sample, including the addition of the reagents. Read the percentage transmittancy of the sample a t 470 mp against the prepared blank. Then read the
