Scholars' Mine Scholars' Mine

Masters Theses Student Theses and Dissertations

1926

A study of electrometric methods for determining selenium and A study of electrometric methods for determining selenium and

tellurium tellurium

Bertie Lee Browning

Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses

Part of the Chemical Engineering Commons

Department: Department:

Recommended Citation 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 scholarsmine@mst.edu.

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 methodsf~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.

fReprint from the Journal of the American Ch~nlic.l Society, 4at 1:.39 (1926).]

The Electrometric Determination of Telluriumin 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 INTHE 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 excessof potassium dichromate has been shown by Lenher and Wakefield! tobe applicable to the volumetric determination of tellurium. 'The purposeof this investigation was to study the applicability of the electrometricmethod 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 thefollowing reaction: 3Te02 + K2Cr207 + 4H2S04~ 3H2Te04 + ~S04+Cr2(S04)3 + H 20, the excess of dichromate being titrated against ferroussulfate. It was found that selenium dioxide is not affected by potassiumdichromate under similar conditions.

Method and Materials.-Samples of pure tellurium-dioxide or aliquotportions of a stock solution of the same material were used. The telluriumdioxide was dissolved in a very small amount of sodium hydroxide solu­tion, 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 10 0 0.2527 5 -0.14 0.180 0.1390 .2527 5 - .06 .10Part 20 .0556 .1015-

.4023 7 .06 .20Part 30 0 .2520 3 + .13 .130.062-0.500 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 200cc. A small excess of 0.1 N potassium dichromate solution was added andthe solution allowed to stand for 45-60 minutes. The excess of dichromatewas titrated against a standard solution of ferrous iron (ferrous ammoniumsulfate), using an Eppley titration apparatus.

A ratio between the potassium dichromate and ferrous irQn solutionswas determined at the close of each day's work. The dichromate solutionwas standardized against specially purified tellurium dioxide.

Part 1 of the table shows that tellurium dioxide is quantitatively oxi­dized to, the telluric state by potassium dichromate, and that seleniumdioxide has no effect upon the determination. Selenium. dioxide in quan­tities up to .2780 g. does not affect the titration of potassium dichromateby .ferrous sulfate.

Part 2 indicates the accuracy of the method for various amounts oftellurium dioxide in the presence of selenium dioxide.

Part 3 indicates that tellurium dioxide may be accurately determinedin the presence of both selenium and copper.

Summary1. Tellurium in large or small amounts may be rapidly and accurately

determined by oxidizing with an excess of potassium dichromate andtitrating the latter electrometrically with ferrous sulfate.

2. Small amounts of selenium and copper do not interfere with thedetermination.

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 ITitration 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,

gm

.0

.0278

.0555

.0836

.111,2

.13,90

.27'80

oc

20.00;20.0020.0020.0020.00'20.00'20.00

FeS04 required

ce

24.3824.~O

24.3724.3924.3224.4424.34

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

.2.520

.2520

.2520.

.2520,

.2520

.2.520

.2,520

gm

ooo

.062:,

.125'

.250

.500

TeO' 2', f Ol~U1d

gm

.2:.52l

.2523·

..2.,52-0

..2'52:'0

.2520

.Z5·~9

.2,517

Error

gm

+.QOO'1+.0003

.0000

.0000

.0000-.0.001-.00:03'

{be} 1.5~ ee: RZS04 sp. U. 1 ..84~, 200 cc voltune

Te.02' taken SeOZ taken CUS04.•5H2~ taken Te02 -round '~Q;r'

...2.047

.2089

grrl

.0555

..0550".·125,"..125

gm.

.:a044~

.2089

gm

~.O-OQ3

.OO·OQ·

.01.58 gm to .1270 gIn' llave n.o e'f'fec·t upon. the determina-

tiO'Il Q'£ tell.tlrium' by t~.is metho-d. Table IV (b') indic:a.tes

tha.t telluri.um Ina¥ b·e determined ver~r aecu.ra.t.e:~y in tile

pres:e·nce Qf' small amount.s o·f bet!! s:e'lenium and copper ..

page 7

~~THOD AND MATERIALS:-

Samples of pure ~e02 or aliquot portions of

a stock solution of the same material were .used.

The ~e02 was dissolved in a very small amount of

sodium hyd.roxide solution, and sufficient dilute

acid added to bring the final acidity to the proper

value. Water was added so that in each case the

volume was 200 cc. A sma.ll excess of NllO .K2Cr207

solution was added and the solution allowed to stana

45 minutes to one hour. The excess dichromate was

titrated with a standard solution of ferrous iron,

(ferrous BJPJIlonium sUlfate) t using an Eppley titrat10n

appara.tus.

A ratio between the potassium dichromate and

ferrous iron solutions was determined at the close

of each day'S work. The dichromate solution was stan­

dardized on specially purified Te02•

page 8

SUMMARY:-

1. Tellurium may be determined rapidly and

aocurately electrometrically.

2. The method is accurate for both large

and small amounts of tellurium.

3. Small amounts of selenium and copper do

not interfere with the determination.

THE ELECTROThtETRIC DETER]:!INATION OF SELE~rIUM

AND TELLURIU~~ BY IVIEMTS OF POTASSIUl[ PER~WTGL~.A.TE.

INTRODUCTION

Previous investigators have discovered that

selenious and tellurious acids may be quantitatively oxi­

dized by potassirum permanganate in aoid solution.

Brauner* reported that in the reaotion with tellurious

aoid permanganate is not rednaed to its lowest state of

valenoe. but to higher hydrated oxidase He also showed

that the reaotion is not quantitative in fairly aonoen­

trated sulfurio acid solation, due to loss of oxygen,

Gooah and Danner ** reduced the error to a negligible

figure by carefully limiting the oonoentration of Bnl-

furio aoid. Goooh and alemons*** suocessfully determ1n~

ed selenious acid by oxidation with potassium permangan-

ate.

The present investigation was to study the

electrometrio determination of both selenium and tellnr-

ium by the use of potassium permanganate.

* Qhem.Soc. 59 .238 (1891)**jm. lel. 44, 301 (189a)***tm. Sci. 50,51,.(1895)

The chemioal

the manganese dioxide whioh precipitated was reduaed very

slowly by the ferrous sulfate. In many oases it was

doubtful whether the manganese dioxide was all reduoed at

the apparent endpoint, since a small amount remained as a

stain on the glass.

The results obtained in the first determinations

varied greatly, and the odor of chlorine was observed

during the titration. Since no hydrochloric aoid or

ohlorides were added. the question ar'ose as to the souroe

of the ahlorine. Systematic examination of the chemicals

used revealed that the sodium hydroxide which was used to

dissolve the tellurium dioxide oontained a considerable

amount of ohlorides. On adopting the procedure of dis­

solving' the tellurium dioxide directly in sulfuric acid,

the presenae of chlorides was avoided and no more d1~fi­

cnlty was experienoed from this souroe. Manganese sul.­

fate and phosphoria acid in varying amounts, both sepa­

rately and together, were added in an attempt to prevent

the aetion of the permanganate on the chlorides present.

This prooedure was unsuooessful, chlorine being liberated

as before. ~he addition of 41sodlum phosphate, and of

suffiolen~ 804ium sulfate to oonvert all of the sulfuric

aoid present to sodium acid su1fate. faile4 to prevent th

liberation of ohlorine. The conolusion was, therefore,

that the titration cO'll1d be carried out suceessfully only

in the absence of ahlorides.

It was found that the addition of phosphoric

aald or disodium phosphate prevents the precipitation of

manganese dioxide·. »isodium phosphate was used since

ita addition does not inorease the acid concentration.

On adding potassium permanganate to a selenium or tell~

urium solution oontaining disodium phosphate, the sol~

nt10n beoomes deep brown in oolor until an exoess of per­

manganate 1s present when it beoomes purple oolored.

The data obtained shows oonclusively that the

method is very accurate for the determination of either

selenium or tellurium. If both are present in the same

sample, they may be accurately determined by a combination

of the permanganate and dichromate methods.

l.m'TH ODS OF ANALYS IS -

The fo11owing prooedure for the determination

of either selenium or tel1urinm was used and is recommend­

ed. A sample containing from .14 to .20 sa. of the'Gx1de

1s weighed and dissolved in 25 00 of 4~ sulfurio aoid.

In the case of tel:Lur1UJD dl xii. t the sample must be .arm­

• ~tl1 solatiQD 1s complete. The solution is iil-tel

'reactions involved are as follows:

KgMn208~5Se02+3R2S04+2H20~K2S0,+2MnS04+5E2Se04

KZMn208+5Te02+3H2S04+2R20~ K2S04+2MnS04+5K2!e04

The reactions are oomplete in a short time, and

manganese dioxide preoipitates. The precipitation of

manganese dioxide necessitates the addition of an excess

of potassium permanganata, the excess being destroyed by

a reducing agent. Gooch and @lemons added an exoess of

standard oxalic aaid solution and then titrated the 8X-

cess with standard permanganate solution.

In the electrometric method, the exoess of po~

tassium permanganate was titrated with ferrous salfate

solution. The ohange in potential is moat marked when

passing from oxidation to reduction potential. A ti-

tration Ollrvs between po,tass1um permang'snate and ferrous

sulfate was determined. The setting of the potentio~

meter at the steepest port~on of the ourve indicates the

greatest ohange of potential with the addition of ferrous

sulfate, and was taken as the endpoint of the titration

in subsequent determinations.

!he investigation showed that two difficultie8

must be overoom.e. !he permanganate reaated with hydro-

chloric aoid or ohlorides present during titration, and

--2-

to 150 CC 9 and 12 gm of disodium phosphate added. A

standara solution of potassium permanganate is added to

about 10 co in ex.cess. and the solution allowed to sta.nd

10-30 minutes. The excess of permanganate is then

titrated eleotrometrically with ferrous sulfate solution.

If selenium and tellurium are to be determined

in the same sample, two methods are available.

(1). The tellurium m~v be determined by oxidizing

with an excess of potassium dichromate, the excess of

diohromate being titrated eleatrometrioally with ferrous

Bulphate by the method of Sohrenk and Browning*. An

excess of potassium permanganate is then added, and the

selenium determined.

(2). The selenium and tellurium may be determined

together by oxidation with potassium permanganate. ~he

tellurium is then determined on a separate portion by

the use of potassium dichromate, and the selenium found

by differenoe.

*Am. Ohem. So. 48, 139 (1926).

rba3n3

Placed Image

Figure I.

This curve shows the change in potential

obtained on titrating potassium pennanganate with

ferrous sulfate in sulfuric acid solution.

-,-

TABLE" I

Titration ourve o:f FeS04

a.nd KMn04

00 FeS04

o5

1015202530354041424343.243.343.444454648

Potentiometer reading

148.4148.3148.3148.3148.3148.0148.1148.5148.0147.4146.8146.21~6.8

11'7.6112.4108.0102.4

99.09'7.8

Table I shows the titra.tion of 30 co of perman..

ganate solution by ferrous Bulfate solution.

~ABLE II

Gravimetrio analysis of 8902 and fe02

average purity

8e02

takengm

1. .2rt752. .2'1753 ••2'175

TeO2

TeO takengm 2

'I•• 24902. .24733 ••25024 ••2489

5e foundgm

.1959

.1959

.1961

Te foundgm

.1993

.1973

.1996

.1982

SeO foundgm 2(oalo)

.2750

.2150·

.2753

TeO foundgm 2( oalc}

.2493

.2468

.249'1

.24'78

SeQ found~ 2

99.1099.1099.21

99.14%

ieo2 found

100.1299.'1999.8099.66

average pur i ty 99.8~

!he S8Q2 and Te02 used were analysed gravimet­

rioally by the method of Lenherand Kao* with the

~esult. shown in Table II.

* • Chem. oa. 47. ?69, (1925)

Table III.

Time reaction of Se02 and Te02

J?a.rt (a)-

Se02 taken KMn04 usedgm cc

Timemin ..

l. 52. 103. 154. 205. 25

Part (b)-

.1372

.1372

.~~72

.~372

.13?2

23 ..6~23.6023.6423.6523.66

Se02 foundgm

.J.368

.1:367

.13'70

.].370

.1371

erl"orgm

--.0004-.0005-.0002-.0002-.0001

Time Te02 tal'Cen KMn04 used Te,02 found av. dey.lnila. cc cc gm from avg.

1.. 52. 103. 154.. 205.. 25

757575757'5

2.8.oa28.0'1

. 28.0928.1028.~2

.2329

.2328

.2330·

.2331

.2332

-.0001-.0002..OOOC+.0001+.0002

Tab1e III shows that the oxidati.on is cOIrij?~ete

within five minutes.

Table IV

Influence of Na~04

1~a·2HP04 Se02 precip- KMn°4 Se02 errortaken itate used found

gm gIn co gin. gIn

l. 1 .~400 yes 25.52 .~~97 --.00032. 2· .~4.00 yes· 25.56 .~3·99 -.00013. 4. .1.400· yes 25.6~ .1402 ~.OOO2

4. 8 .1400 none 25.64. .1404 +.00045. ~2 .].400 nOlle 25.66 .1405 +-.0005

The inf~uence of the amount of disodium phos-·

phate present is shown in table IV. In genera~~ it may

be s.tated that 12 gm. of l~a2HP04 in 200 ce of solution will

prevent the precipitation of manganes.e dioxide formed by

the reduction of 25 ee, of N/l.O permanganate for at period

of one hour. The amount necessary to prevent precipi-

tatiQn increases viith the time of standing and wi th the

amount of permanganate reduced •

....1.1..

Tab~e V

L'1.f~uenc.e of K2SO'4

SeQ H2S0 KMnO',4 SeQ error2 a.dde~ 2taken used :foundgm cc cc gm gIn

~. .l4.Ql 1 25.60. .~40~ .00002. .1.401 3 25.6~ .1402 ~.OOO~

3'. .1.401 8. 25.64. .1404 +.00034.• .~401 ~4 25.67 .1405 '+.00045. .J..401 20 25.74. ..1409 +.0008

The ~imits wi thin which the co'ncentration of the

sulfuric acid may vary without impairing the accuracy

of the determination are indicated in tab1e V: Thia

sho~vs that the ti tration may be successful~y carried

out in, concentrations of sulfuric acid of from .9% to

1.3% by we·ight (.5% to· 7% by vo~ume).

Tab:le· VI

Ratio of Na~04 and H2SO4

SeQ2 Na2HPO'4 H2SO4 KYn<J4 se02 error'taken used found

gm. gm cc· ce gm gm

1. .1.378. 6 1.0 25.35 .1315 -.00032. ..~37a 6 15 25.34. .1.374 .... 00043. .l378 6 20 25.45 ..1~80 +-.00024. .~378 6 25 25.46 .~38:l +.00035. .~378 ~1. ~O 25.29 .1372 -.00066. .1.378 l~ l5 25.33 .l374 --.00047. .~3~7.8 11 2.0 25.42 .1379 +-.000l.8.• . 3'78. l~ 25 25.49 .1382 +.00049. .1378 ~6 lO 25.33 .J.3'14 -.0004

10" .13'18 l6 l5 25.36 .J.375 -.0003ll. .~378 l6 20 25.39 .137rz ... 000112. ..~378 ~6 25 25.44 .1380 +.00021.3~ .1.378 2l. lO 25.30 .1.372 -.0006·~4. ..~378 2l l~) 25.35 .13'75 ... 000315. .~378 21 20· 25.45 .1.380 +.000216. .~378 2l. 25 25.54 .~385 +-.0007

Table VI shows tha,t the ratio of disodium phosphate

to sulfuric acid was found to be without effect. within

the limits of acid concentration described above.

Table VII

Influence of excess of YJm04

Se02 ' KMnO& EMn04 seOZ errortaken adcte used

gm co co gm gIn

1. .1371 Z4.94 25.20 .1367 - •. 00042 • •1371 34.94 25.22 .1368 - .00033. .1371 34.94 25.18 .1366 - .00054. .1371 34.94 25.18 .1366 -.00055. .1371 39.93 25.25 .1369 -.00026. .1371 40.93 25.19 .1366· -.00057. ~1371 39.93 25.20 .1367 -.00048. .1371 39.93 25.22 .1368 -.OOO~

9. .1371 49.91 25.27 .1370 -.000110. .1371 49.91 25.29 .1371 .000011. .1371 49.91 25.27' .1370 -.000112. .1371 49.91 25.32 .1373 +.0002

Table VII shows the influence of the amount

of excess of potassium per~Bnganate added. The amount

of excess present can vary from 40 to lOO~ of tha a­

rrtount used. without influencing the results of the ti-

tration.

-14-

Titra:tion. of SeOa.

S'e()2 taken. IQ1n04 uaeclgnl ce

Par"t fa}

Se02 foundgm

Err~r'

gm

1.. .J~3?6

2. ..l~76··

S. ..1376'4.. ...1.376

Far··t, (b)

5. 0-13756.. .1.3'75''1.. ..·~374

8., ..I375S. .lS75

F'art {el

10••1375'11.••.1.3'7512••13"75,

25~~..26:2,5 ..2,52.5 ...2-525 ..25

2.5.3425.32..25 ...3,~25 ..3l25~.~4.

Z5'.32,2~5.2,9

2,5.2'1

..1.377

...1-3.';6;.

..1.376

.IZ~rz6'

.l~?4

...13,73

...1.~7~~1.::;~:3~

..1.3'74.

~1.374

..1372

..l3?1.

+..,0001­...0000.0'000.'.000..0·

-.ooo·!-- ..0.00'2~.QQO'2,

-.0001

~.ooo·~

.....0.00.;;:

....O·004~

Tab.le VIrr re~o:r·d.s:, a. t J"1'ical. dat.a.. sheet. Qf" a

seriea o·f' d..e"terrr.Linatio.na b~"- tIli.S: me',tl1o,d. and. in.dicat.••

..15-

Titr&i.,i.an of TeOZ

Kllh04 us'ed Te.OZ :round..cc gm

1..2-..3.4.5.6.?8.9 ..10 •1, •12....13.14-:.

TeOz. takengm

~:L9'al.,

..197rz:

.1983•.1.9·7.4­..~9!'l~

'..19:75.1.986..I9~'13..1.99:7• 1.984.• 2.0,02.1.9.90..19,82,.1-98&

26.(1(1:25'.9"Z2.,5: ..9:'1.25~65

2.5..SO·25~ ..6Z25.6,825 ..6~2.5 ..'1'6:,2:5" ..542,5.?92.5 ..6-32.5.5425 ..6"6:

.2QSS

.2028

.2026'

..2000:

.1994

.2004

.2008

.2003

.2.0I~4,

~1997

~2~O,17'

.200,4:

..2Q06:

..2JQQ'l

Errorgm

~..OQ'52"'-.005,1....{),04$-f-.OOS2.T.OOZl+.002.9+...002.2,+.oo~o

-r:.0017+..aC.13+.OO;~5·

+..0014+.0024+.002:5

Tah1e lX records a. series' of' deternlinat,io·ns of

~e()~ in which chlorides: I'er·e known t,o b,e present and the

Q:dar o-f escap'i.n.g' free ef'.ll.orine was no,ticed. The 'Varianee

in re-sults obta.ined. YlaJ3 therefore t.o be EaI1ec"tec..

Table X

Ti.trati.o.n of Te0 2

TeO:2 taken KMn°4 used Te02 fecund erl"orgm C.C gm gm

Pa,rt ('a}

~. ..19.87 25.60 .l992 +.00052. .1988 25 .. 62 .1.994 +.00063. .1987 25.59 .1992 +.000·54. .1990 25.62 .199~. +-.0004..5~. .~990 25.64 .~996 +-.0006'6. .1987 25.57 .1.990 +.OOO~

'1. .1.993 2.5.59 .i992 .... OOO~8. .1989 25.53 .1987 ~.OOO2

9. .1983 25.42 .1978 ... 000510. .1998 25.69 .~999 +.OOO~

11. .1989 25.58 ..199~ +-.000212. .1989 25.55 .1989 .00001:5. .1984 25.51. .1986 +.,00021.4. .1984 25.50 .1985 .....0001

PaJ!t (b )

1.5. .1984. 25.36 .1983 .... OOO~16:. .1984 25.36 .1983 -.0001,1'7. .1984- 25.S5 .1.982 -.000218. .1984 25.35 .1982 --.0002

The resul ta· l.isted in table X sho,w the accuracy

of tlle method for tel~urium in ti trati,o.ns in which.

chlorides are known to be absent.

Tab1e XI

Titratio·n of varying amounts of TeO'2

Te02 talc.en KMn° 4 used Te02 found errorgm cc gin gm

1. .0052 .69 .0054 +-.00022. ..O~96 2.56 .O~99 +.00033. .050'4 6.58 .0512 +.00084. .1006: ~2.95 .1007 +.OOO~

5. .2,000 25.76 • 2004 +'.0004.6. .2997 38.52 .2997 .00007. .3994. 51,.3~. .3994 .0000

Tab~.e XI shows the· ac·c.uracy of the method :Cor

varying amounts of Te.02t. from .0050 gm to .4000 gm..

Tabl.e X.II

Titration D·f SeO'2 and TeO'2

Part (a )

Te.02 Se02 KMnO'4 Te.02 errortaken taken used found

g.m gm cc gm gm

1. .O~OO .1.375 26.70 .O~O5 +.00052. .0696 .~375 34.38 .0702 +.00063. .1.501. .1375 44.55 .~494. -.000'14. .2.002 .~.S75 51.02 .~997 -.00055. .2509 .~:575 57.04. .2l1.9 -.0300

Part (b: )

Te02 Se.02 KMh04 SeO'2 erro.rtaken taken used found

gm gm cc gIn gIn

6. .1997 .0055 26.90 .0064 .... 00097'. .. 2002 .0269 30.66 .0265 -.00048. .2007 .0545 35.83 .0542- -.00039. .1991 .0814. 40.60 .0910 -.0004

~O. .l983 .1,091 45.59 ..108? -.0004

~1.9..

In ord.er to determine whether the method could

be applie.d to the determination of varying amounts of

se~enium and te~lurium together, the data shown in

tab~e XII \vas determined.. The results were calcu1a­

ted as fol~ows: In part (al a constant amount of se­

~cnium was added, the amount of perr.aanganate required

for i t calculated from the standa,rdization. and the re ..

mainder of the potassium permanganate used to calculate

the tel~urium found. In part (b} a constan t amount of

tel~urium was added, the amount of permanganate re­

quired for it calculated from the standardization. and

the remainder of the potassium permanganate used to

calculate the selenium found. Tl1e a.ccuracy of this

procedure is sho~vn by the results recorded.

-21-

In order to find whether selenium and tellur­

ium could be determined in the same sample, the data

of table XIII was taken. ~he selenium and tellurium

were oxidized together by potassium permanganata. the

tellurium determined in a separate sample by potassium

dichromate, and the amount of permanganate required by

the tellurium in the first case calculated. The amount

of permanganate remaining was used to oalculate the se­

lenium found. This procedure is shown to be qUite ac­

curate for the determination of selenium, and the a­

mount of tellurium may be readily determined from the

dichromate titration.

-22-

Tabl.e XIV

!itratioD. o~ Te02. and SeOa: with K2~ra97'"then wi t.h KMn07.

T'e(l2 takengm

Se02.' -t·aken. DJ104 used. Se02,: :round hro-r

grll ec gm wn1.. ..0701.2:.. ..O:?·O~

~.. .0701

.13'74.

..~;3·'l4

.1374

~·.50'

23 ..'7823.'13

.I3'l9

.};5·77

.13?fi

".0005~,..0003+..0001

In a mixtur'e' whi,ch c~ont,ai.ns both s'ele,nium and.

t.el.ltlr:ium~ the t.eI.luritml madi be oxi.dized. t-o the tellur'ie

sta.te by pota.s:s.i:l..1m di..c·bromate and. the· excess. of the la.t.ter

de:s.troyed, by el,eetrome·tri.e titrat,ion with f'erroua B'tb1fa..t.e.

Tl-re s-e'l.eni-um. mq- b'e then determined by oxidat,ion with

pQ,tassium permanganate in the usual mann~er;. rypieel.

re·mtl'ts"; are shown in tabIe XIV.

-2Z-

SUMlvlARY: -

(1). Selenious and tellurious acids may be

very accurately determined by oxidation with potassium

permanganate and titration of the excess of the latter

electrometrically with ferrous sulfate solution.

\2). Chlorides must be absent.

(3). 1he addition of disodium phosphate pre­

vents the precipitation of manganese dioxide.

(4). Selen.ions and tellurious acids in the

same samples may be determined by using a combination

of the dichroma~e and permanganate methods.

-24-

Bibliography

1. Potentiometric Titrations. Kolthoff and Furman.

Wiley. (1926).

2. The volumetric determination of tellurium by

the dichromate method. Lenher and rrfakefield. J. Am.

Chern. Soo. 45,1423, (1923).

3. The electrometric titration of dichromate with

ferrous sulfate. Eppley and Vosburgh. J. Am. Chem.

Soc. 44~ 2148, (1922).

4. Some applications of the hydrogen electrode in

. analysis, research and teaching. Hildebrand. J. Am.

Chem. Soc. 35, 847, (1913).

5. The increase in oxidizing potential of the di­

chromate ion on platinum caused by certain reducing

agents. An improved method for the electrometria ti­

tration of ferrous salts. Forbes and Bartlett. J.

Am. Chem. Soc. 35, 1527, (1913).

6. Volumetric estimation of telluriu~. Brauner. J.

Am. Cham. Soc. 59, 2~8, (1891).

-25-

7. On certain points in the interaction of po~

tassium permanganate and sulfuric acid. Goo-ch

a.rld Danner. .An1 .. J. Sci. 44~ 301. .. (1.892.).

8 ~ The separation. of seleni um and tellurium.

Lenher and Kao. J. Am. Chem. Soc. 47, 769 a (~925).

9. The determination of selenious acid by potassium

permanganate.. Gooch and C·~emons. .Am •. J" .. Sci 50,

5~. (1895).

~o. The electrometric determination of tellurium

in the presence of ferri.c iron. se~enium and copper ..

Schrenk and Browning .. J. Am. Chem. Soc .. 48. 139,

(192.6 ).

-25-