Scholars' Mine Masters Theses Student Theses and Dissertations 1926 A study of electrometric methods for determining selenium and tellurium Bertie Lee Browning Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Chemical Engineering Commons Department: Recommended Citation Browning, Bertie Lee, "A study of electrometric methods for determining selenium and tellurium" (1926). Masters Theses. 4707. https://scholarsmine.mst.edu/masters_theses/4707 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. A STUDY OF ELECTROMETRIC METHODS FOR DETEmlINING SELENIUM AND TELLURIUM. BY B. L. Browning A TJIESIS submitted to the faculty of the SCHOOL OF MINES AND METALLURGY OF THE UNIVERSITY OF MISSouRI in partial fulfillment of the work required for the Degree of MASTER OF SCIENCE IN CH~~ICAL ENGINEERING Rolla,![o. 1926 Approved by 7.~ t . Associate ~rofessor of Chemistry The2ia~ A study of ~lect~o~8tric methods f~Jr detel.'mir... ing sel'3:::::_~l>:'e t ..lid teJl~)J:·iu!L. :2.rowniE~~. J.926. The anthor- wish.es: t· expres.s: apprecia.tion t,o Dr.· W. T. ScllrenIc fo~' the su.ggestion of tlli.s: research.,. and far TC;1~l.uab:le advice- and sugge·stions gi.ven whi~e the work was in progress. Table of Contents Part 1. The electrometric determination of tellurium in the presence of ferric iron, selenium and copper. Introduction••••.••••••••.••••••••••••••••••page 1. Tables and disoussion.•••.•••••••••••.••••••page 3. IJlethod and materials•••••......•...••...••..page 7. Summary••••••••••••••••••••••••••••••••••••• page B. J:Jart 2. The electrometric determination of selenium and tellurium by means of potassium permanganate. Introduction•••••••.••••••••••.•••••.•.•••••page 1. Methods of analysis•••••••••••••••••••••••••page 4. Titration ourve .••••••.•••••••••••••••••.•••page 5. Tables and discussion.~•••••.•••.•••.•••••••page 8. Summary •••••••••••••••••••••••••••••••••••••page 24. Bibliography•••••••••••••••••.••••••••••••••page 25. Ch~nlic.l fReprint from the Journal of the American Society, 4a t 1:.39 (1926).] The Electrometric Determination of Tellurium in the Presence of Ferric Iron, Selenium and Copper By 'w. T. Schrenk and B. L. Browning [Reprint from the Journal of the American Chemical Society, 48, 139 (1926).J [CONTRIBUTION FROM THE CHEMICAL LABORATORY, MISSOURI SCHOOL OF MINES AND MSTALLURGY] THE ELECTROMETRIC DETERMINATION OF TELLURIUM IN THE PRESENCE OF FERRIC IRON, SELENIUM AND COPPER By W. T. SCHR.ENK AND B. L. BROWNING REcsrVllD SSPTEMBER 8, 1925 PUB~ISHED JANUARY 8, 1926 The quantitative oxidation of tellurous acid to telluric acid by excess of potassium dichromate has been shown by Lenher and Wakefield! to be applicable to the volumetric determination of tellurium. 'The purpose of this investigation was to study the applicability of the electrometric method to this titration. In converting Lenher and Wakefield's method, with slight modifications, to an electrometric titra-tion, to avoid the use of a spot plate. indicator, their results as a whole have been verified. The method is based on the following reaction: 3Te02 + K 2Cr207 + 4H2S04 ~ 3H2Te04 + ~S04 + Cr2(S04)3 + H 20, the excess of dichromate being titrated against ferrous sulfate. It was found that selenium dioxide is not affected by potassium dichromate under similar conditions. Method and Materials.-Samples of pure tellurium-dioxide or aliquot portions of a stock solution of the same material were used. The tellurium dioxide was dissolved in a very small amount of sodium hydroxide solu­ tion, and sufficient dilute acid added to bring the final acidity to the TABLE I TITRATION OF TELLURIUM DIOXIDS 10-20 ce. of H2S04 (d. 1.84) CuS04.5H20 SeOt TeOt No. of Error of Av. deviation taken. g. taken, g. taken, g. analyses average, mg. from avo mg. Part 1 0 0 0.2527 5 -0.14 0.18 0 0.1390 .2527 5 - .06 .10 Part 2 0 .0556 .1015- .4023 7 .06 .20 Part 3 0 0 .2520 3 + .13 .13 0.062-0.500 0 .2520 4 .10 .10 .125 .0556 .2068 2 .15 .15 1 Lenher and Wakefield, THIs JOURNAL, 45, 1423 (1923). 140 w. T. SCHRENK AND B. L. BROWNING Vol. 48 proper value. Water was added so that in each case the volume was 200 cc. A small excess of 0.1 N potassium dichromate solution was added and the solution allowed to stand for 45-60 minutes. The excess of dichromate was titrated against a standard solution of ferrous iron (ferrous ammonium sulfate), using an Eppley titration apparatus. A ratio between the potassium dichromate and ferrous irQn solutions was determined at the close of each day's work. The dichromate solution was standardized against specially purified tellurium dioxide. Part 1 of the table shows that tellurium dioxide is quantitatively oxi­ dized to, the telluric state by potassium dichromate, and that selenium dioxide has no effect upon the determination. Selenium. dioxide in quan­ tities up to .2780 g. does not affect the titration of potassium dichromate by .ferrous sulfate. Part 2 indicates the accuracy of the method for various amounts of tellurium dioxide in the presence of selenium dioxide. Part 3 indicates that tellurium dioxide may be accurately determined in the presence of both selenium and copper. Summary 1. Tellurium in large or small amounts may be rapidly and accurately determined by oxidizing with an excess of potassium dichromate and titrating the latter electrometrically with ferrous sulfate. 2. Small amounts of selenium and copper do not interfere with the determination. RO~~AJ MISSOURI • 1'l-Ij£ :3L2~CTI~OIviETRIC DETERI\'~INATION O:B' TELLURImr Il~ THE PRESENCE 0]' FERRIC IRON, SELENIUM, AND COPPER. Introduction. The quantitative oxidation of tellurious aoid to telluric acid by potassium dichromate has been shown by Lanher and Wakefield* to be applicable to the volumetric determination of tellurium. The purpose of this investigation was to study the applicability of the electrometric method to this titration. Hildebrana** and many others have discussed in recent literature the applicability of oxidation potentials to the electrometric method of titration. G. S. Forbes and E. P. Bartlett*** demonstrated the possibility of using the electrometric method for ti­ trating potassium dichromate with ferrous sulfate. Eppley and Vosburgh**** showed that this titration could be carried on successfully in hydrochloric and sulfuric aci,d solutions. and that, the concentrations of these acids could vary within wide limits. * J. Am. Chern. Soo •• 45, ~423 (1923) ** J. Am. Chern. Soc •• 35,' 847 (1913) *** J. Am. Chem. Soc •• 35, 1527 f 1913) **** J. Am • Cham • Soo •• ' 44, 2148 (.1922) In converting Lenhar and 'Wakefield's method, with slight modifications, to an electrometric titra­ tion, to avoid the use of a spot plate indicator, their results as a whole have been verified. In addi­ tion, it was discovered that selenium dioxide or se­ lenious acid is not oxidized in sulfuric acid solution by potassium dichromate. rhe method is based on the following reaction: 3Te02+K2Cr207+4H2S04~3H2Te04+K2S04+CrZ{S04)3+H20 Selenium dioxide is not affected by potassium dichromate under similar conditions. page 3 T'ab-le I Titration of Te02 1.7 ae H2:S04 sp. gr. 1.84. 200 cc volume Te02 taken 8e02 taken K2Crz0 7 used TeOa found Error gm gm 00 gm gil .2527 0 31.42 .2526 -.0001 .2527 0 31.40 .. 2,525 -.0002 .25'27 0 31.44 .25'28 +.0001 .2527 0 31.• 40 .2525 --.0002 ~2,52.7 0 31.~8 .2524 -.0003 .2.52,7 .1390 31.45 .2529 +.0002 .252.7 .1390 31.45 .2529 +.0002 .25'2.7 .1390 31.43 .25'27 .0000 .2,52,7 .1390 31.43 .252,7 .0000 .2,52,7 .139·0 31.42 .2526 --.0001 Tab1e I shows that tellurium dioxide. is quan~ titativelY oxidized to the telluric state by potassium dichromate in sulfurie acid solution and that the presence of quantities of selenium dioxide up to .1Z~O gm has no effeot upon the determination. page 4 Table II Varying amounts of 8802 10 cc R2S04 sp. gr. 1.84~ 200 co volume. 8e02 taken, FeS04 required gm oc ce .0 20.00; 24.38 .0278 20.00 24.~O .0555 20.00 24.37 .0836 20.00 24.39 .111,2 20.00' 24.32 .13,90 20.00' 24.44 .27'80 20.00 24.34 Table II shows that selenium dioxide is not oxidized b~ potassium diahromate in sulfurio said of the above coneentration. The amount of selenium diox~ ide pres,ant; up to .2780 gm. has no effeot upon the tl~ tration. Table III Varying amounts of Ta02 15 cc H2S04 sp. gr. 1.84, 200 co volume 1}.1 eO 2 taken SeOZ taken 'TeOZ found. Error gm gm gm gm .1015 .0556 .1013 -.0002 .1521 .0556 .1521 .0000 .2018 .0556 .2020 +.0002 .2517 .0556 .2517 .0000 .3026 .0556 .3026 .0000 .3531 .0556 .3530 -.0001 .4023 .0556 .4013 -.0010 Very pure 1'602 was prepared. Varying amounts were weighed out and determined in the presence of 8e02- The results tabulated in Table III give evidence of the accuracy of the method for varying amounts of Te02 in the presence of small amounts of Se02. {a} 20 ec: H~04 sp. gr'. 1 ..84" 200 ee vol'llme TeO 2 t:a.ken TeO' 2', f Ol~U1d Error gm gm gm .2.520 o .2:.52l +.QOO'1 .2520 o .2523· +.0003 .2520. o ..2.,52-0 .0000 .2520, .062:, .. 2'52:'0 .0000 .2520 .125' .2520 .0000 .2.520 .250 .Z5·~9 -.0.001 .2,520 .500 .2,517 -.00:03' {be} 1.5~ ee: RZS04 sp. U. 1 ..84~, 200 cc voltune 5H2~ '~Q;r' Te.02' taken SeOZ taken CUS04.• taken Te02 -round grrl gm.