The Catalytic Effect of Osmium Tetroxide on the Oxidation of Hydrazine by Potassium Chlorate Citation Stone, Donald Stuart (1927) The Catalytic Effect of Osmium Tetroxide on the Oxidation of Hydrazine by Potassium Chlorate. Bachelor's thesis, California Institute of Technology. doi:10.7907/0HWT-WM67. https://resolver.caltech.edu/CaltechETD:etd-12062004-140817 Abstract No abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: Chemical Engineering Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: None, None Defense Date: 1 January 1927 Record Number: CaltechETD:etd-12062004-140817 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-12062004-140817 DOI: 10.7907/0HWT-WM67 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 4810 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 08 Dec 2004 Last Modified: 03 Oct 2019 23:38 Thesis Files Preview PDF (Stone_ds_1927.pdf) - Final Version See Usage Policy. 507kB Repository Staff Only: item control page

THE CATALYTIC EFFECT OF OSMIUM TETROXIDE ON THE OXIDATION OF HYDRAZING BY POTASSIUM CHLORATE Thesis by Donald §. Stone In partial fulfillment of the requirements for the degree of Bachelor of Science in Chemical Engineering. CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 1927 THE CATALYTIC =FFECT OF OSMIUM TETROXIDE on the OXIDATION OF HYDRAZINE BY POTASSIUE CHLORATE Introduction It is well known that neutral or weakly acid solutions of alkali chlorates show no appreciable oxidizing power. How- ever, it has been observed by K. A. Hofmann (Ber. 45,3329, 1913; 46,1567,1913) that, in the presence of very minute smounts of osmium tetroxide, the oxygen becomes readily available. Chlorate solutions activated in this way will, for example, oxidize hydrazine to free nitrogen, potassium iodide to iodine, and ersenic to arsenious acid. Hofmann found that, in the oxidation of hydrazine sul- fate, nitrogen is liberated quantitatively according to the equation SNHa NHg Hp SO, + 2KC10z = 3N5+ 3Hp SO, + 8KC1+ 6H20 The investigation of the mechanism of this reaction has been taken as the subject of this thesis. Experimental Work Hydrazine sulfate was prepared by the method of Conant (Organic Syntheses, V¥.8, P.31). The resctions involved are; 2Na0H + Cl, = NaOCl + Nacl + Hd NaOCl + NE, = NHoCl + Naok NHj0l+ NeOQH+ NH, = WNHp' NH, Tae sodium hypochlorite solution was prepared by passing + Nadl + HO Chlorine into a 61. flask containing 480 gm. of sodium hyroxide, 2400 gm. of water, and .8400 em. of cracked ice until the flask had gained 340 gm. in weight. During the addition, the flask was kept thoroughly cooled in order to savoid the formation of chlorates. To each of four 1200 cc. batches of the sodium hypochlorite solution was added 1500 cc. of concentrated ammonia water, 900cc. of water, and 375 cc. of a 10% gelatine solution. These mix- tures were evaporated as rapidly as possible to about one-third the original volume. The residual solutions were cooled with ice and filtered; then cooled again with ice and salt. When the temperature reached 0°, an excess of concentrated sulfuric acid was slowly added with constant stirring. When the hydra- zine sulfate had completely precipitated it was filtered off and washed with cold alcohol. Avout 220 grams of hydrazine sulfate were obtained, cor— responding to a yield of 35% on the basis of ammonia used. One re-crystallization yielded a product which was almost entirely free from chloride. The first experimental work done wes an attempt to follow the rate of the reaction by measuring the liberated nitrogen. For this purpose the apparatus sketched on p. 3 was constructed. It consists essentially of a reaction flask (A) equipped with a mercury seal stirrer (B), a dropping funnel (¢), connected at the top to the delivery tube (D), which, in turn, is connect- ed to the gas burette (H#), through the two-way stop-cock (PF). A water reservoir (G), is connected at the bottom of the burette to equalize pressures when making readings. APPARATUS __—formeasuring. rave of METRIC GASO of Nitrogen. . trolution In operating this asvaratus, the reaction flask, contain-— ing the potassium chlorate and osmium tetroxide solution, was immersed in a thermostat. The hydrozine sulfate solution was put in the dropping funnel, and all connections were thoroughly coated with paraffin. Then the stirrer was started and the water level in the burette brought to the zero point, pressures in both the burette and the reaction flask being adjusted to atmospheric by opening the air vent (EH). The stop-cock (F) was then turned to shut off the air vent and /é8nnect the burette with the delivery tube. Then the stop-cock (H) on the dropping funnel was opened and the hydrazine sulfate solution was sllow ed to enter the reaction flask. The volume of nitrosen evolved at. successive tine intervals was read from the burette, pressures being equalized by bringing the water in the reservoir to the level of that in the burette. A great many trials were made in an effort to gét consis- tent results with this apparatus. One of the chief difficulties was the impossibility of maintaining a uniform rate of stirring, because of continual voltage fluctuations in the power supply. Since the relative heights of the mercury coluwns in the stirrer are dependent on the velocity of revolution, variations in speed caused marked discrepancies in the burette readings. Further- more, it was found that, in order to avoid large errors due to supersaturation of the solution with nitrogen, a very high stirring velocity (1000 to 1500 r.p.m.) wes necessary. Repeated atteapts to construct a stirrer that would run at this rate for a sufficient length of tine were unsuccessful. These ditficul- ties finally made it necessary to abandon the gasometric method. Various methods of analyzing the solution for chloride and hydrozine were tried. The oxidizing action of the chlorate and ossmium tetroxide prevented the use of the ordinary iodimetric methods for hydrozine; and the silver-chromate determination of chloride was useless because of the reducing action of the hy- drozine. It was found, however, that silver chloride could we precipitated without appreciable reduction, provided the solu- tion was one-tenth normel or stronger in nitric acid. On this basis the following procedure was adopted: Stock solutions of hydrozine sulfate, .15 molal; potassium chlorate, .20 molal; and Osmium tetroxide, 1 mg. per cc., were made Ups These were kept in the thermostat and portions pipetted into reaction flasks to give solutions of the concen~ trations noted below for the rate experiments. For each anal- ysis 25 cc. was pipetted from the reaction flask to a beaker contsining 10 cc. of tenth normal silver nitrate solution, 3 cc. of 6N nitric acid, and 100 cc. of water. After a minute or two of stirring, the precipitate coagulated/i# wes filtered through a weighed Gooch crucible, washed, dried and weighed. The results of experiments performed are given below: Run No. 1 ‘ . - oy, . oe me) ra Concentrations: K01l0,, .08 molal; NoH4H9804, 108 molal; QOsO,, .04 mg. per cc. Time in Hours Grems of Agol i 0017 2 | .0037 Time in Hours Grams of Agcl 3 0054 4 0070 s) 0088 6 .O101 7 .O115 8 0130 10 .O154 34 -0335 Run No. If Concentrations: KG10,, -08 molal; NgH4H2504> 108 molal; Os0,, .08 mg. per cc. Time in Hours Grems of Agel 1 0043 2 .0078 3 01138 4 -01438 5 0168 7 0226 3 0287 11 0347 23 0695 28 . 0967 335 - 1330 464 1335 o>) Run No. III Concentrations: K010g, .08 molal; Ng4kgS0, | (015 molel « 2 Os04> -OS me. per cc. Time in Hours Grams Agol 4 0337 8 0339 13.2 -0338 al 0344 Run No. IV Concentrations: KC10., .02 molal; Nghghgs0 4 | -O6 molal; Os04, .O8 mg. per cc. Sime in Hours Grams AgOl 4 0031 B 0048 13 0054 23 -0080 Run jo. Concentrations: KO10., -O8 molal; Notghy SO, , .035 molal; Os04, .OS mg. per ce. Time in Hours Grans Agel 1 0083 2 0168 8 0643 4,25 0685 Time in Hours Grams Agol 5 .0668 6.2 0667 8 0683 18 0684 Run No. VI Concentrations: KC10,, .04 molal; NgHgHeso,, -06 molal Os04, -O8 Mg. per cc. Time in Hours Grams Agcl 1 0023 2 0041 3 .0048 5 0061 8 - 0084 18 0114 The above data are plotted on Page 9. Discussion of Results A comparison of curves IV and VI shows that each ordinate on VI is approximately twice the corresponding ordinate on IV, indicating that the rate of formation of KCl is directly pro- portional to the chlorate concentration. (Curve II shows this same relation for the first 3 or 4 hours, but later, as the hydrozine concentration decreases, it becomes proportionately faster.) Similarly, curves I and II indicate that the rate is directly proportional to the Os04 concentration. But a com- i yy 0.02 © 08 | i t i 0.08 | 0.04M. 108 | w .08 nig fcc __s” Hours 16 ao a2 24 26 28 30 10 perison of curves II, III, and V shows that the rate is much greater with a lower hydrozine concentration. This effect is also indicated by the shape of curves I, II and V. The effect of catalysts in promoting oxidation~reduction reaction generally consists in the catalyst being alternate- ly oxidized and reduced. It is highly probable that the first reaction which takes place in our case is the reduction of the osmium tetroxide to a lower oxide. In view of the effect of hydrozine on the reaction rate, it seems probable that more than one lower oxide of osmium is formed. We shall assume for the moment that the reduction takes place according to the following equations: (1) Os04+NoH, = 080g + Ng + BH0 (2) Os0g+ ANoM, = O80, + 3NQ + BQO The corresponding oxidation equations are: (3) BKC10., t 30805 = ®8KCl +t 3080, (4) KC10z + 3080, = Kel + 30804 The ratio of the rates, Vy and V5, of reations (1) and (2) respectively is: V ky (NoH,) (08024) 1 L \83"4 4 = = = K VNoH, Vv = 2 Kg YNgHa . (os04) | . it is evident, then, that increasing the hydrogine concen- tration increases the rate of reaction (1) more than that of reaction (2), thereby increasing the Os0s concentration and diminishing the OsO, concentration. Now, if reaction (3) is slow as compared to reaction (4), the net result of increasing ii the hydrogine concentration is to slow up the reaction as a whole. | The presence of osmium ‘dioxide may be recognized by the fact that it appears as a dark colored colloidal solution. In the foregoing experiments it was noticeable that the solutions with the higher concentrations of hydrozine were distincly darker in color. This investigation was carried out at the suggestion and under the direction of Dr. Don M. Yost. Summary The rate of reaction of potassium chlorate with hydrozine sulfate in the presence of osmium tetroxide has been determined for various concentrations of the reacting substances. It was found that the rate varies directly with the concentration of chlorate and of osmium tetroxide, but inversely as a function of the hydrozgine concentration. A reaction mechanism which is in accordance with these observations has been proposed.