I. The Permanganate Titration of Thallous Salts Ii. The Determination of bismuth by Caffeine Tetraiodobismuthate(Iii)

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DOCTORAL DISSERTATION SERIES

i

TITLE

Q

AUTHOR

UNIVERSITY

r.

DATE

ImMIJM

0

1

'

2

jj UNIVERSITy MICROFILMS *

ANN ARBOR ■ MICHIGAN

ACKNOWLEDGMENTS The author wishes to express M s sincere appreciation for the aid and counsel given him by Dr, A, Witt. Hutchison in Part I and for the advice and many helpful suggestions given him by Dr. G. C. Chandilee throughout the work.

TABLE OF CONTENTS ACKNOWLEDGMENTS THE PERMANGANATE TITRATION OF THALLOUS SALTS INTRODUCTION............. .............. EXPERIMENTAL.............. ............. RECOMMENDED PROCEDURE................ . ACKNOWLEDGMENTS..................... . SUMMARY

.......................

THE DETERMINATION OF BISMUTH BY CAFFEINE TETRAIODOBISMUTHATE (III) INTRODUCTION............................ SUBSTANCES AND SOLUTIONS................ PROCEDURE

..........................

SEPARATION AND DETERMINATION OF BISMUTH IN THE PRESENCE OF OTHER IONS............. INTERFERING IONS........................ SUMMARY................................. BIBLIOGRAPHY

/

THE PERMANGANATE TITRATION OF THAT.r.nng SALTS Since Willm (1) first noted the necessity for chloride ion in titrations of monovalent thallium with potassium per­ manganate solutions, other investigators (2, 3, 4, 5, 6, 7, 8, and 9) have made the same observation under various con­ ditions . They, however, obtained high results, the diver­ gence being greater with small concentrations of thallium. The work of three of these Investigators is of partic­ ular interest.

Hawley (3) reported his results in terms of

a factor, gm. Tl/cc. KMn04 ,

He found that hot solutions,

containing in a total volume of 60 cc. 4 cc. of HC1 (sp. gr, 1.2) and about 0.1 gm. of thallium equivalent to 35 cc. of his permanganate solution, gave nearly constant factors but that solutions containing smaller amounts of thallium gave lower factors. lutions.

He also obtained similar results in cold so­

Berry (5), following the method of Hawley, made a

few titrations using an electrometric apparatus to determine the end point and obtained results 3$ high for a solution containing 0.0563 gm. of thallium in 60 cc.

He reported

satisfactory results for a solution containing 0.253 gm. of thallium in this volume.

Swift and Garner (8) varied the

concentration of HC1 from 0.5 H to 1.0 M and the temperature from 55°C. to 90°C. but the end point was uncertain and the results were from 0.6$ to 0.7$ high.

They also observed

little or no improvement upon addition of phosphoric acid alone or with manganous sulphate, addition of potassium

chloride, or use of the iodine monochlorlde end point. It seems to be generally believed that the high results obtained in the permanganate titration to a visual end point are due to oxidation of chloride ion.

Since very little in­

vestigation of the electrometric end point has been reported, it seemed worth while to determine whether satisfactory re­ sults could be obtained by this method.

Also, since no in­

vestigations of permanganate titrations in solutions con­ taining fluoride ibn have been reported, the results of such

i

a study are presented in this paper. EXPERIMENTAL Substances and Solutions.-

The thallium solution was pre­

pared by dissolving approximately 6.68 gms. of thallous ni­ trate (C.P. Elmer & Amend) in two liters of distilled water to give an approximately 0.025 N solution.

It was standard­

ized by two different methods and concordant results were obtained. In one method (10), 30.00 cc. of the solution in a beak­ er were heated to 90°C., 1.0 cc. of HC1 (sp. gr. 1.2) was added and the thallium precipitated immediately by the addi­ tion of 1.0 cc. of a 10# platinum chloride solution.

The

mixture was digested at 90®C. for one hour, cooled to room temperature, and filtered on a G-4 Jena sintered glass fil­ tering crucible.

The precipitate was washed with cold water,

dried in an electrlo oven at 90°C. to 100°C., cooled in a desiccator and weighed.

From the weight of thallium chloro-

platinate, the normality of the solution was calculated. In the second method (11 and 12), 3.0 cc. of HC1 (sp. gr. 1.2) were added to 50.00 cc. of the thallium solution previously heated to 90°C. and containing two drops of a saturated solution of methyl orange and the mixture was ti­ trated rapidly with 0.1 N potassium bromate solution until the indicator was decolorized. The following table shows the agreement between the re­ sults from these two methodsrMethod PtCl4 KBr03

Solution 1 0.02584 N 0.02583 N

Solution 2 0.02525 N 0.02530 N

A stock solution of approximately 0,1 N potassium per­ manganate was prepared and allowed to stand in the dark in a brown glass bottle for six weeks.

From time to time as nec­

essary, 500 cc. of this stock solution were filtered by suc­ tion through an alundum orucible and diluted to two liters to give a solution approximately 0.005 M.

To standardize the

solution, sodium oxalate (C.P. U. S. Bureau of Standards), dried at 130°C. for one hour, was used in 0.14-gm. portions each dissolved in 150 cc. of water acidified with 4.0 cc. of sulphuric acid (sp. gr. 1.84)j titrating at 60°C. to 85°C. All other materials were of C.P. or equivalent grade. In all of the titrations which follow, the total volume of each solution at the start was 60 cc. and when there was appreciable evaporation during a titration, the volume was returned to 60 cc. by the addition of water.

A microburette

4. was used for volumes below 10.00 cc.

other conditions are

set forth in the various experiments. 9

Titration of Thallous Salts with Permanganate. Visual End Point.—

Titrations at 65^C« to 70^C. were carried out on

solutions 0.8 M in HC1 and varying in thallium content from 0.01541 gm. to 0.1233 gm.

The results are given in Table I

along with the times, of duration of the pink color at the end of the titrations.

The rapid disappearance of this color

resulted in overtitration in each case and was apparently diie to the reduction of permanganate by hot HC1.

This would ex­

plain the curve obtained by Hawley (3) since, with increas­ ing concentrations of thallium in solutions containing the same concentration of chloride ion, the overtitration effect becomes relatively less important and a nearly constant fac­ tor would be expected.

Also, while it was possible to obtain

satisfactory results in a few cases, the short duration of the end point makes the method undesirable.

i

Titrations at room temperature (23°C.) were carried out on solutions 0.8 M in HC1 and varying in thallium content from 0.00804 gm. to 0,1206 gm.

The results (Table II) were

all high ranging from 1.7$ to 12.0$ and are further verifi­ cation of Hawley*s work (3).

The thallium precipitated as

the monochloride in the more concentrated solutions but rei dissolved as the titration progressed. A brown color ap­ peared and finally a brown precipitate shown qualitatively to contain manganese settled out.

This indicated the incom-

Table I Visual Titration in Hot 0.8 M HC1 Solution Gm. T1 Taken 0.01541 0.03082 0.04622 0.06163 0.07704 0,09246 0.1079 0.1233

Gm. T1 Pound 0.01607 0.03104 0.04628 0.06191 0.07716 0.09284 0.1081 0.1237

Duration of End Point 50 sec. 30 " 25 " 25 M 20

5 5 5

"

■ " *

io Error 4.4 0.7

0.1 0.5 0.2 0.4 0.2 0.3

Table II Visual Titration In Cold 0,8 M HC1 Solution Gm. T1 Taken 0.00804 0.01608 0.02413 0.03217 0.04825 0.07237 0.09651 0.1206

Gm. T1 Found 0.00900 0.01748 0.02524 0.03290 0.04955 0.07425 0.09852 0.1226

& Error

12.0 8.8 4.7 2.0 2.7 2.6 2.1 1.7

7. plete reduction of permanganate in the cold solution and ac­ counted for the overtitration in this method. Titration of Thallous Salts with Permanganate. Electromatrlo End Point«~

Titrations at 85 C, to 90^C. were attempted on

solutions containing 0.02609 gm. of thallium and varying in . HC1 concentration from 2 M to 5 M.

These could not be car­

ried out because the galvanometer would not indicate a steady voltage.

For concentrations of HC1 from 0.7 M to 0.1 M, the

rate of oxidation of thallium deoreased successively as was shown by the slower rates at which the voltage reached a con­ stant quantity.

A series of titrations at 65°C. to 70°C. was

carried out on solutions 0.8 M in HC1 and varying in thallium content from 0.00770 gm. to 0.1233 gm.

Table III gives the

results of this last series. It will be noted that the errors are predominantly in the same direction, the results being low, and that in one extreme case the error is 20$.

To determine whether this ef­

fect was due to air oxidation, solutions containing definite weights of thallium and 0.8 M in HC1 were heated on a hot plate at 65°C. to 70°C. for one hour, the maximum time re­ quired for electrometric titrations.

The thallous thallium

was then precipitated and determined by the platinum chloride method (10),

The results (Table IV) show air oxidation of

0.7$ to 4.8$ of the original thallium content.

Hence, al­

though the electrometric titrations were carried out in such a way that only a small fraction of the monovalent thallium

8..

Table III Eleetrometrlc Titration in Hot 0,8 H HC1 Solution Gm. T1 Taken 0.00770 0.01541 0.02311 0.03082 0.03852 0.04622 0.05393 0.06163 0.06934 0.07704 0.08474 0.09245 0.1002 0.1079 0.1156 0.1233

Gm. T1 Found 0.00755 0.01538 0.02301 0.03078 0.03855 0.04619 0.05415 0.06154 0.06926 0.07738 0.08458 0.09216 0.09949 0.1073 0.1149 0.1223

# Error -20.0 -0.2 -0.4 -0.1 0.1 -0.1 0.4 -0 *1 —0.1 0.4 -0.2 -0.3 -0.7 -0.6 -0.6 -0.8

Table IV Air Oxidation In Hot 0.8 M HC1 Solution Gm. T1 Takftw 0.03082 0.06163 0,09245 0.1233

Gm. T1 Pound 0.02938 0.05911 0.08969 0.1224

$, Oxidized

4.8 4.1 3.0 0.7

10. was present for any considerable time, the permanganate being added rapidly until within 1.0 cc. of the end point, an ap­ paratus was assembled for titrations in a nitrogen atmosphere to prevent air oxidation.

At first, nitrogen was bubbled

through the solution, but, when it was seen to cause an un­ steady voltage when used in that manner, it was blown over the surface of the liquid in the titration beaker during the entire titration.

The HC1 was not added until the nitrogen

had blown over the surface of the hot mechanically stirred solution in the beaker at least five minutes, thus assuring removal of dissolved oxygen. A series of titrations at 65°C, to 70°0, was carried out in a nitrogen atmosphere on solutions 0,8 M in HC1 and varying in thallium content from 0,00783 gm. to 0.1252 gm. The results (Table V) show a precision of 0.4# in solutions containing a minimum of 0.03131 gm. of thallium.

The pre­

cision varied from 0.6# to 1.0# in the more dilute solutions of thallium. The practicability of electrometric titrations in a ni­ trogen atmosphere at room temperature (23°C. to 24°0.) of so­ lutions varying in thallium content from 0*00783 gm, to 0.02381 gm. and in HC1 from 0.2 M to 0.8 M was studied.

i

The

rate of reaching equilibrium as evidenced by the drifting in voltage was slower in the lower molar concentrations of EC1. The solutions turned brown and a brown precipitate, shown qualitatively to contain manganese, began to settle out in

Table V Electrometric Titration in Hot 0.8 M HC1 Solution Nitrogen Atmosphere Gm. T1 Taken 0.00783 0.01565 0.02348 0.03131 0.04696 0.06262 0.07827 0.00392 0.1096 0.1252

Gm. T1 Found 0.00787 0.01579 0.02362 0.03134 0.04706 0.06238 0.07805 0.09375 0.1096 0.1251

% Error

0.5 0.9 0.6 0.1 0.2 -0.4 -0.3 -0.2 0.0 . -0.1

Gm. T1 Found 0.00792 0.01573 0.02357 0.03132 0.04717 0.06235 0.07811 0.09367 «.1095 0.1250

Error 1.0 0.7 0.4 0.0 0.4 —0.4 -0.2 -0.3 -0.1 -0.2

12. each case when the titration was within 1.0 cc. of the theo­ retical end point.

The voltage fell slowly after sharp in­

creases upon each addition of permanganate before the end point was reached and drifted slowly upward for over 30 min­ utes after the addition of 0.02 cc. of titer in excess of that calculated to be equivalent to the monovalent thallium. Summary of Visual and Electrometric Titrations.-

The results

of these titrations are represented in Figure 1 which shows by means of the factor, gm. Tl/cc. 0.005 M KMn04 , the locations of points with reference to a theory line drawn on the plot.

Thus, overtitrations give points below while underti­

trations give points above the line.

The summary follows

(a) Titrations to visual end point on hot solutions gave nearly constant factors for a minimum thallium content of about 0.041 gm. (Hawley's minimum (3) was about 0.1 gm.) but all of the factors were low because of oxidation of HC1, (b) Titrations to visual end point on cold solutions gave nearly constant factors for a minimum thallium content of about 0.033 gm. but each involved a large overtitration due to incomplete reduction of permanganate as evidenced by the formation of a brown precipitate containing manganese. (c) Electrometric titrations of hot solutions with con­ centrations of HC1 from 0.1 M to 5 M indicated that the most satisfactory concentration was 0,8 M since higher concentra­ tions tended to give unsteady potentials and lower concen­ trations reduced the rate of reaching equilibrium.

However,

Figure 1 Permanganate Titrations of Thallous Solutions Mg. Tl/Gc. KMh04 2.625 03

2.575

O

Theory

O

O (9 ri n

©

9

© 40

©

-

3 ©

O

.4 3

o. s O (1 (3

n

O u U/ ®

3

'

a W

(*P)

3

3

2.525

C ©

€ €

€

20

30

2.475

31 < 2.4£5 10

40

Cc. 0.005 M KMn04 1. Hot solution with visual end point 2. Cold solution with visual end point 3. Hot solution with electrometric end point 4. Hot solution in nitrogen atmosphere with electrometric end point 5. Cold solution in presenoe of fluoride with visual end point

50

14, such titrations gave predominantly high factors subsequently found to be due to air oxidation.

Other titrations in a ni­

trogen atmosphere gave nearly constant factors for a minimum thallium content of about 0.031 gm. with error less than 0.4# in any case.

Smaller concentrations of thallium showed

larger errors with a maximum of 1.0# for 0.0078 gm. (d)

Titrations to electrometric end point on cold solu­

tions were found not to be feasible because of the slow rate at which equilibrium was reached. Titration of Thallous Salts with Permanganate in the Presence of Fluoride Ion.-

In this series of experiments, the effect

of fluoride ion upon the permanganate titration of thallous salts was studied.

It was necessary to consider the fact

that in an acid solution containing a large excess of fluowIde ion the heptavalent manganese is reduced to the trivalent state and unites with fluoride ion to form the complex ion, MnPg*.

Hence, for a 4-vclent change, the permanganate re­

quired in the fluoride ion solution was 1.25 times that re­ quired for a 5-valent change in the solution containing no fluoride Ion.

Fluoride ion in the following experiments was

introduced by means of powdered NaF placed directly in the titration beaker.

A series of titrations using equivalent

quantities of KF.SHgO gave results in agreement with those obtained using NaF,

The NaF has the slight disadvantage of

producing a cloudy mixture in some titrations because of its low solubility.

This effect, however, did not obscure the

15 •

end point. Titrations to visual end point were carried out at room temperature (27°C. to 28°C.) on solutions 0.8 M in HC1, 0.8 14 in NaF, and varying in thallium content from 0.00641 gm. to 0.00483 gm.

A faintly brown coloration appeared as the titra­

tion progressed but the permanganate end point was visible and all of the titrations gave satisfactory results as shown in Table VI.

The agreement with theory is further illus­

trated in Figure 1 in which the averages of these data, rep­ resented by closed circles, have been calculated to an equivalent basis. Table VII and Table VIII show the results of experiments designed to study the effect of varying the concentrations of EC1 and NaF in solutions containing in the first case 0.03914 gm. and in the second case 0.03842 gm. of thallium.

Table

VII shows that the solution must contain a large excess of fluoride ion above that required for the formation of theo­ retical complex ions both of manganese and thallium, and that chloride ion is a necessary catalyst for the oxidation of thallium in fluoride ion solutions.

Table VIII shows the

maximum permissible molarities of HC1 for various molarities of NaF in addition to the effects of these molarities upon the titrations as a whole. Titrations to visual end point were carried out at room temperature (23°C.)

on solutions 1.2 M in HClj 1.2 M in NaF,

and varying in thallium content from 0,02569 gm. to 0.07707

16

Table VI Visual Titration In Cold Solution Containing Fluoride Ion Gm. T1 Taken 0.00641 0.01288 0.01922 0.02563 0.04870 0.07177 0.09483

Gm. T1 B'ound 0.00648 0.01287 0.01928 0.02558 0.04856 0.07165 0.09481

& Error

1.1 0.4 0.3 -0.2 -0.3 -0.2 -0.0

Gm. T1 Found 0.00644 0.01280 0.01924 0.02554 0.04856 0.07173 0.09471

$ Error 0.5 -0.2 0.1 -0.4 -0.3 -0.1 -0.1

Table VII Effect of Varying Normality of NaF and HC1; Constant Acidity T1 taken = 0.03914' gm. Hz S04 N a p \ H01 0.8 N 0.6 N 0.4 N 0.2 N 0.12 N 0.04 N

0.1 N 0.7 N

0.3 N 00.5 H

0.5 N 0.3 N

0.03919 0.03921 0.03914 0.03914 0.03885 0.03806

0.03921 0.03014 0.03914 0.03909 0.03913 0.03780

0.03905* 0.03907* 0.03896* 0.03871* 0.03869* 0.03867*

0 .7 N 0 .1 N TOO Too Too Too Too Too

slow slow slow slowslow slow

*The rate of oxidation of the thallium is very slow and the end point is therefore uncertain.

18.

Table VIII Effect of Varying Molarity of NaF and HC1 T1 taken = 0.03842 gm. ^HCl NaF 0.8 1.0 1.2 1.4 1.6 1.8 2.0

M M M M M M M

0.8 M

1.2 M

1.6 M

Satisfactory 0.03852 0.03852 0.03831 0.03848 0.03852 0.03844 0.03844’ 0.03848 0.03852 0.03837 0.03852 0.03848 0.03850 0.03856 0.03856 0.03852 0.03856 0.03854 0.03848 0.03852 0.03852 Cloudy Clear throughout.

2.0 M 0.03795 0.03823 0.03811 0.03837 0.03837 0.03854 0.03852

2.4 M 2.8 M Low results. 0.03686 0.03483 0.03797 0.03513 0.03773 0.03570 1 0.03756 0.03745 0.03839 0.03767 0.03839 0.03797 0.03842 0.03845

at end point.

10. gm.

The results were satisfactory as shown in Table IX,

Further Investigation of Electrometrlo Titrations,-

Three e-

lectrometric titrations in nitrogen atmosphere at 65°C. to 70°C. were carried out on 0.8 M HC1 solutions containing 0.02641 gm. of thallium in addition to 3.0 cc. of phosphoric acid solution (85$) in one case, 0.8 mole of NaF in the sec­ ond, and both 3.0 cc. of phosphoric acid solution (85$) and 0.8 mole of NaF in the third.

Phosphoric acid alone greatly

reduced the rate of reaching equilibrium, and therefore the method is impracticable.

When phosphoric acid was used with

NaF, a pink color appeared at about halfway during the titra­ tion and persisted thenceforth, the results being much too low.

The results from the titration using NaF alone agreed

with those obtained from a fourth titration of the same amount of thallium in 0.8 M HG1 solution containing no fluoride ion. As indicated on pages 10-12, electrometric titrations in cold solutions 0.8 M in EC1 were found to be impracticable due to formation of a brown precipitate.

It seemed advisable

to Investigate further electrometric titrations in cold solu­ tions but with higher concentrations of HC1.

It was found

that when the solution was 1.2 M in HC1 there was no precip­ itate of manganese but the results were low and, as before, a long time was required to reach equilibrium.

Electrometric

titrations were also carried out in solutions 1.2 M with re­ spect to EC1 and 1.2 M in NaF.

The rate at which Bqullibrium

Table IX Visual Titration in Cold Solution Containing Fluoride Ion Gm .T1 Taken 0.02560 0.03853 0.05138 0.06422 0.07707

Gm. T1 Found % Error 0.2 0.02574' 0.1 0.03857 0.1 0.05141 0.06400 -0.2 -0.0 0.07705

Gm. T1 Found & Error 0.02572 0.1 0.1 0.03855 0.0 0.05130 0.06410 -0.0 0.1 0.07711

was reached was again slow and the results were slightly low. Figure*2. shows the curves for these electrometric titrations at ropm temperature (27.5°C.).

j

It is Interesting to compare the values of the poten­ tials for these solutions when half oxidized with the stand­ ard oxidation potential, -1.25 v. (13), for the system T1*-T1*** based on studies made in other mineral acid solu­ tions.

The value, referred to the normal hydrogen electrode,

of about -0.729 v. obtained in the case of the solution free from fluoride indicates clearly the strong tendency of trivalent thallium to form complex chloride ions.

This phenom­

enon causes also a very real dependence of the oxidation po­ tential on the chloride ion concentration of the solutions as was shown some time ago by Spencer and Abegg (14).

These au­

thors reported a value of -0.859 v. for a solution 0.105 M in HC1 and -0.828 v. for one 0.190 M in HC1. By analogy to ferric ion, the existence of a stable fluorothalllate complex ion might be expected.

Although such an

ion may be formed, the value of -0.815 v. obtained when thal­ lium is half oxidized in the presence of fluorides indicates that its stability, if greater, is evidently not much more so than the corresponding chlorothalliate ion.

It is not imme­

diately evident why the potentials obtained with fluoride present are larger than those found in their absence.

In

view of the profound influence of the chloride ion concen­ tration on the T14~T1*** potential, it is perhaps worth

22. Figure 2

Against

Saturated

Calomel

Cell

Potentiometric Titrations of Thallous Solutions

0.9

0.8

0.7

tic 0 , 6

Qt

P H !> 0.5 0

10

20

30

40

50

Cc. 0.004770 M KMn04 The solutions had the same thallium content. The curve to the right was obtained in the presence of fluoride.

23. noting that the mean ion activity coefficient of HC1 in gen­ eral is greater than that of NaCl in moderately strong solu­ tions.

Thus| for 1 M solutions at 25°G., the value for HC1

is 0*823 and for NaCI is 0*650 (15).

If the complex ion is

assumed to be TIClg* and with the rough approximation of fur­ ther assuming all of the sodium fluoride converted into so­ dium chloride and neglecting other factors, the above activ­ ity coefficient data lead to a potential difference of 12 mv» between the two solutions.

The experimental difference shown

by the curves is about 16 mv. for solutions somewhat less concentrated in HC1. Beyond the end point the potentials are lower when flu­ orides are present* minished acidity.

This is probably due in part to the di­ However, the break is great enough to

yield a satisfactory potentiometric end point.

24. RECOMMENDED PROCEDURE

j

Of the two satisfactory methods evolved in this work for the determination of thallous salts, namely, the electromet» ric titration in nitrogen atmosphere in hot 0.8 M HC1 solu­ tion and the visual titration in cold fluoride ion solution, the latter obviously is to he preferred because of its great­ er convenience. To a total volume of approximately 60 cc. containing 6,0 cc. of HC1 (sp. gr. 1.2) and thallous ion between 0.006 gm. and 0.1 gm., add three grams of powdered NaF.

(Instead of

powdered NaF, a filtered solution containing 7.0 gms. KF.2HgO may be used).

Titrate with 0.005 M KMnO^ solution to a faint

pink color which should persist for several minutes.

A

faintly brown coloration may appear as the titration pro­ gresses but the permanganate end point is clearly visible. It is to be noted in making the calculations that the normality of the permanganate solution, when used with fluor­ ide ion, is four times the molarity.

Thus, if the permanga­

nate has been standardized by sodium oxalate, the normality so obtained should be multiplied by 0,8 to obtain the normal­ ity for titration in the presence of fluoride ion. (cc. X N) KMnB4 x 204.4 T1 = ---- — -----------------

2000

25. ACKNOWLEDGMENTS Grateful acknowledgment Is madie to Prof. H, H. Geist, ^tr* • J. R. Hayes, and to several senior students; of Prof'. T. ■m

«v. Mason for making titrations to check the redomisiended pro­ cedure • SUMMARY The work of previous investigators has been confirmed end the high results generally obtained, have been explained! a s being due to oxidation of HC1 in hot solutions, and incom­ plete reduction of permanganate in cold solutions. Electrometric titrations have been extensively studied »rnj found to be satisfactory in hot 0.8 M HC1 solutions under a nitrogen atmosphere and containing as little as 0.03 gm. of 'thallium..

The nitrogen atmosphere is necessary to prevent

air oxidation of thallium in hot HC1 solutions. A new method has been developed for the satisfactory ti­ tration of thallou3 salts with permanganate.

The method in-

■gpolves the use of excess of fluoride ion in cold solutions. The fluoride ion nullifies the error normally encountered in c e o Id

solutions by stopping the reduction of all the perman­

ganate at the trivalent state.

THE DETERMINATION OP BISMUTH BY CAFFEINE TETRAIODOBISMUTHATE (III) Many organic bases have been used as precipitaats in analytical chemistry,

A few of these are known to form in­

soluble complex iodo metallic compounds from which the metal may be determined by titration of the iodine from the com­ plex ion.

Several determinations of bismuth have been made

by this ntethod,

Hexamethyl dliododiamino isopropyl alcohol

(16 )t n^phtkoquimolime (17 and 18), 8-hydroxyquinoline (17, 19, 20, and 21), 8-nitroquinoline (22), quinine (23), quin­ oline (2-4;), quirtaldine (25), dithiocyanato diethylemediamim® cobalti thiocyamate (26), trietftarlenediamlne cobalti chlo­ ride (2?), and antipyrine methyleneamine (28) form complex compounds with bismuth and iodine and methods using the3e bases hatve been reported for the determination of bismuth, Preliminary^ tests with caffeine showed that it may be satisfactorily used to determine bismuth.

An insoluble com­

pound of caffeine, bismuth, and iodine is formed containing the atoms of bismuth and iodine in the ratio of 1:4,

It was

also evident that mercury formed no insoluble compound and. hen©e it was possible to devise a method for the determina­ tion of Tadsmuth in. the presence of mercury.

So far as it

has beem possible to determine, similar methods for bismuth previously reported have all required the absence of mercury.

27. SUBSTANCES AND SOLUTIONS Caffeine sulphate solution was prepared from 133 guts, of caffeine (Eastman Kodak Company) dissolved in 570 cc. of 6 N sulphuric acid, then diluted to one liter.

Bismuth ni­

trate solution, containing 2.79 gjns. of the C. P. salt per liter of 1% nitric acid solution, was standardized with con­ cordant results by the phosphate and carbonate methods.

The

same 25-cc. pipette was used in measuring bismuth solutions for both standardization and separation.

Table I shows a

typical set of bismuth nitrate standardizations.

Potassium

iddate solution was made to contain 2.0480 gms. of the C. P. salt per literj 1.00 cc. of this solution being equivalent to 0.0010 gm. of bismuth.

The potassium iodate solution was oc­

casionally standardized against dry U. S. P. potassium iodide and found in each case to have been stable (29).

All other

reagents used were of C. P. grade. PROCEDURE Dissolve the sample (containing about 0.03 gm. of bis­ muth) in a mjrtinram of sulphuric acid, dilute to 150 cc. in a 4'00-cc. beaker, and adjust the acidity to about 1 N.

(De­

terminations were carried out in solutions containing up to 6 .5^ acid by volume). tion.

Add 30 cc. of caffeine sulphate solu­

Stir vigorously during the dropwise addition of 2.0

gms. of pure potassium iodide dissolved in 25 cc. of water. Let stand about ten minutes, then filter by suction through

28.

Table I

A Typieal Standardization of Bisraoth Nitrate Solution

Carbonate Method

Sample 1 2 3

Gnu Bismuth/25 ca. 0.0300 0.0299 0.0301 Phosphate Method!

Sample 1 2 3

Gm. Bismuth/25 ccc. 0.0298 0.0298 0.0298

89. asbestos in. a Gooch crucible •

It is not necessary to remove

the precipitate which adheres to the beaker since the same beaker is to be used for the subsequent decomposition of the precipitate and titration.

Wash five times with 15-oe, por­

tions of an aqueous wash solution prepared as follows:- dissolve 1.8 gms. of caffeine in 6 cc. of 6 N sulphuric acid, dilute to about 900 cc., add 1.0 gm. of potassium iodide, then dilute to one liter.

Next, wash four times with 15-cc.

portions of dibutyl ether from which peroxides have been re­ moved by distillation from sodium sulphite followed by re­ distillation from mossy zinc. Place the Gooch crucible containing the washed precipi­ tate in the beaker in which the precipitation was made.

Add

100 cc. of b% sodium hydroxide solution and heat to boiling to decompose the precipitate. HC1.

Cool and add 23 cc. of 12 N

Cool again, then add 8 cc. of KCN solution and titrate

with potassium iodate solution to the iodine cyanide end point according to Lang's method (30). The results of six determinations on solutions contain­ ing 0.0300 gm. of bismuth are given in Table II. For very small amounts of bismuth, smaller amounts of reagents were used.

Thus, for 0.00117 gm. of bismuth, 3 cc.

of caffeine sulphate solution and 0.060 gm. of KI were added for the precipitation.

The precipitate was washed with di­

butyl ether only and was subsequently decomposed by 100 cc. of 0.5fo NaOH solution and titrated by potassium iodate

Table II Determinations on 0.0300 Grant of Bismutli Gnu Bismuth Found 0.0300 0.0302 0.0300 0.0299 0.0299 0.0300

31. solution (1.00 ec. being equivalent to 0.0001 gm. of bis­ muth) ,

The results of a series of determinations on solu­

tions containing 0.00117 gm, of bismuth are givens in Table III. SEPARATION AND DETERMINATION OF BISMUTH IN THE PRESENCE OF OTHER IONS In the majority of eases, the presence of other ions did not interfere with the determination of bismuth by the regular procedure. a few instances.

Slight modifications were necessary in Following are the results of experiments

in the presence of non-interfering ions grouped for con­ venience . Mercury. Bivalent mercury does not interfere with the de­ termination of bismuth by this method provided sufficient KI is added to convert the insoluble mercuric iodide first formed to the tetraiodomercurate (II) ion.

3.0 gms. of KI

instead of the usual 2.0 gms. will be adequate for the sep­ aration of 0.03 gm. of bismuth from as much as 0.20 gm. of mercury as shown in Table IV.

In Table V are listed the re­

sults of five determinations on solutions containing 0.0300 gm. of bismuth in the presence of 0.10 gm, of mercury as nitrate.

Univalent mercury should be oxidized to the biva­

lent before proceeding with the determination since the former is precipitated by KI as unstable mercurous iodide which decomposes to mercury and mercuric iodide.

Table III Detemiaat^Lons on 0.00117 Gt'am of Bismuth Gm. Bismuth Found 0.00116 0.00118 0.00116 0.00120 0.00118 0.00119 0.00120 0.00119

Table IV

Determinations on 0,0293 Gram of Bismnthi with Varying Amounts of Mercury and Potassium Iodide Gm, Hg None

0.10

0,20

0.30

0.40

0.50

KI ' 3.0

0,0289 0.0292 0.0291 0.0294# % I 2 gum Hglg gum 0,0290 0.0293 0.0291 Hgl2 Hglg gum Hgl2 gum

2.0

0.0294 0.0290 0.0295 0.0291

#A small amount of mercuric iodide was noticeable.

Table V Determinations on 0.0300 Gram of Bismuth in the Presence of’ 0.10 Gram of Mercuric Ion Gm. Bismuth Pound 0.0298 0.0299 0.0301 0.0299 0.0301

35. galclurn, Strontium, Sodium f Potassium. and Magna slum. The determination of 0,0300 gm, of bismutli in the presence of a mixture of 0,02 gm. of each of these ions as nitrates was carried out by the regular procedure.

The results of Jfour

determinations were 0.0299, 0.0300, 0.0300, and 0.0302 gm. Beryllium and Uranyl. Pour determinations on solutions con­ taining 0,0300 gm. of bismuth in the presence of a mixture of 0.02 gm. of each of these ions as nitrates were carried out by the regular procedure and gave 0.0302, 0.0303, 0.0304:, and 0.0303 gm. Aluminum^ Iron, Nickel. Cobalt. Manganese. Chromium, and Zinc.

Four determinations on solutions containing 0.0300

gm. of bismuth in the presence of a mixture of 0.02 gm. of each of these ions as nitrates were carried out by the regu­ lar procedure.

The results were 0.0296, 0.0300, 0.0300, and

0.0299 gm. Molvbdate. Pour determinations on solutions containing 0.0300 gm. of bismuth in the presence of 0.03 gm. of molyb­ denum as molybdate ion were carried out by the regular pro­ cedure and gave 0.0303, 0.0304, 0.0301, and 0.0303 gm. Arsenious.

Four determinations on solutions containing

0.0293 gm. of Msmuth in the presence of 0.1 gm. of arsenic as arsenious chloride were carried out by the regular pro­ cedure and gave 0.0295, 0.0292, 0.0292, and 0,0294 gm. Lead and Cadmium. Since lead formed insoluble lead iodide, it was found expedient to precipitate all of the lead by

36. addition of art excess of sodium sulphate before proceeding with the determination.

After the lead sulphate was fil­

tered off , the bismuth was determined by the regular pro­ cedure.

Cadmium did not interfere.

Pour determinations on

solutions containing 0.0300 gm. of bismuth in the presence of a mixture of 0.05 gm, of each of these ions as nitrates gave 0.0298, 0.0297, 0.0303, and 0.0297 gm. Barium.

Since barium sulphate drags down bismuth ion, it

was necessary to modify the procedure.

Caffeine nitrate

solution was made containing 133 gms. of caffeine and 203 cc. of 16 N nitric acid per liter and used instead of caf­ feine sulphate solution. was followed.

Otherwise, the regular procedure

Pour determinations on solutions containing

0.0300 gm, of bismuth in the presence of 0.02 gm. of barium as nitrate gave 0.0300, 0.0301, 0.0298, and 0.0300 gm. Vanadyl. Vanadate ion was reduced by the addition of 10 cc. of 10^ sodium sulphite solution to produce vanadyl ion.

Pour

determinations on solutions containing 0.0300 gm. of bismuth in the presence of 0.03 gm. of vanadium as vanadyl ion were carried out by the rggnlar procedure and gave 0.0303, 0.0299, 0.0299, and 0.0298 gm. St a m i c . It was possible to determine bismuth in the pres­ ence of stannic ion provided sufficient HC1 were added to convert the tin to hexachlorostannate (IV) ion and so pre­ vent its hydrolysis to metastannlc acid.

For 0.1 gm. of

stannic ion, 2.5 cc. of 12 N HC1 were adequate.

After the

37. stannic ion was tied up, four determinations were carried out by the regular procedure on 0.0300 gm. of bismuth and gave 0.0299, 0.0299, 0.0296, and 0.0303 gm. Antlmonous and_ Arsenate. Bismuth was determined in a mix­ ture of 0.1 gm, each of antimony and arsenic present as antimonous sulphate and arsenate ion.

The addlftlon at the

outset of 4 gms. of ammonium tartrate was made to prevent the hydrolysis of antimonous sulphate.

Four determinations

on solutions containing 0.0300 gm. of bismuth gave 0.0301, 0.0300, 0.0302, and 0.0298 gm. Stannous.

After adding 2.5 cc. of 12 N HC1 to prevent

hydrolysis of stannous chloride, four determinations on solutions containing 0,0293 gm. of bismuth in the presence of 0.1 gm. of tin were carried out by the regular procedure and gave 0.0291, 0.0294, 0.0293, and 0.0293 gm. Phosphate. The acidity of the solution before determination must be at least 1 N to prevent the precipitation of bismuth phosphate.

In the presence of phosphate introduced by 0.3

gm. of sodium; ammonium hydrogen phosphate, four determina­ tions were carried out on solutions containing 0.0293 gm. of bismuth and gave 0.0294, 0.0294, 0.0294, and 0.0295 gm. The optimum permissible concentration of HC1 was about 0.15 Nj that produced by the addition of 2.5 cc. of 12 N HC1. A 0,5 N concemtrat ion of nitric acid produced, no undesirable effects.

38. INTERFERING IONS Aa previously mentioned, bismuth could not be deter­ mined in the presence of mercurous ion because the latter is precipitated as unstable mercurous iodide which decomposes to mercury and mercuric iodide.

In addition to this, the

determination could not be carried out in the presence of copper or silver because of the insolubility of their iodides. Also, in the case of copper, am insoluble compound is formed with copper, iodine, and caffeine. SUMMARY A new method for the determination of bismuth has been developed in which the element is precipitated as caffeine tetraiodoMsmuthate (III) and subsequently determined by titration of the iodine. to one atom of bismuth.

Four atoms of iodine are equivalent The method is applicable for as

little as 0.001 gm. of bismuth. The method affords the separation of bismuth from mercu­ ry, a discovery hitherto unreported for this type of analy­ sis.

In addition to mercury, separations of bismuth, by

modified procedures in some cases, can be made from the fol­ lowing ions:- calcium, strontium, sodium, potassium, nickel, magnesium, beryllium, uranyl, aluminum, manganese, chromium, iron, cobalt, zinc, molybdate, arsenious, lead, antimomous, cadmium, barium, vanadyl, stannic, arsenate, stannous, and phosphate.

39. Silver, copper# and mercrurous ions Interfere with the determination of bismuth by this method.

40. b i bl i o g r ap h y

(1)

Wlllm, Brail, soc. chJLra., 5, 352 (1863).

(2)

Noyes, Z. phys. Chem., 9, 608 (1892),

(3)

Hawley, J. A. C. S., 29, 300 (1907).

(4)

Benrath and Espenschied, Z. anorg. allgem. Chem., 121. 361 (1922).

(5)

Berry, J. Chem. Soc., .121, 394 (1922).

(6)

Bodnar and Terenyi, Z. anal. Chem., 69, 33 (1926).

(7)

Proszt, Z. anal. Chem., 73, 401 (1928).

(8)

Swift and Gamer, J. A. C. S., §8, 113 (1936).

(9)

Marshall, J. Soa. Chem. Ind., JJ), 994 (1900).

(10)

Cushman, Am. Chem. J., &g, 222 (1900).

(11)

Kolthoff, Rea. trav. ehim., 41, 172 (1922),

(12)

Zintl and' Rien&aker, Z. anorg. allgem. Chem*, 153. 276' (1926).

(13)

Latimer, "Oxidation Potentials", Preratiae-Hall, 1938, p. 153.

(14)

Spencer and Abegg;, Z. anorg. allgem. Chem., 44, 379 (1905).

(15)

Lewis and Randall, "Thermodynamics", McGraw-Hill, 1923, p. 362.

(16)

Aurisiachio, Industria chimica, 7, 1358 (1932).

(17)

Berg and Wufcm, Ber., 60B, 1664 (1927).

(18)

Hecht and Reissner, Z. anal. Chem., i02» 88 (1935).

(19)

Farirai, Boll* chim* farm*, 75, 284 (1934).

41. (20)

KalthofT and Griffith, Mikrochimiea Acta, 3, 47 (1938).

(21)

Sazerac and Pouzergues, J. Compt. rend. soc. Mol., 109. 370 (1932).

(22)

Canned and Dino, Ann. chlm. appllcata, ££, 455 (1936).

(23)

Francois and Seguin, J. phar. chim., 8 £, 59 (1925),

(24) Gapchenko and Sheintzis, Zavadskaya Lab., £, 835 (1935).

(25) Hayes and Chandlee, Ind. Eng;. Chem., Anal. Ed., 11, 531 (1939). (26) Spacn and Spacu, Z. anal. Chem., 9£, 260 (1933). (27) Spacn and Suoiu,- Z. anal. Chem., 7£, 196 (1929). (28) Takaki and Takaae, J. Pharm. Soc. Japan., 56i 405 (1936). (29)

Jamieson, "Volumetric: Iodate Methods", Chemical Catalog Co., 1926.

(30) Lang, Z. anorg. allgem. Chem., 122, 332 (1922).

%