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

44 Pages·01.679 MB·English

by  Beale, Robert S

DOCTORAL DISSERTATION SERIES
i
TITLE
Q
r.
AUTHOR DATE
I m M I J M
0
UNIVERSITY
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. He also obtained similar results in cold so­
lutions. 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 methodsr-
Method Solution 1 Solution 2
PtCl4 0.02584 N 0.02525 N
KBr03 0.02583 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.
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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 re-
i
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 Gm. T1 Pound Duration of End Point io Error
0.01541 0.01607 50 sec. 4.4
0.03082 0.03104 30 " 0.7
0.04622 0.04628 25 " 0.1
0.06163 0.06191 25 M 0.5
0.07704 0.07716 20 " 0.2
0,09246 0.09284 5 ■ 0.4
0.1079 0.1081 5 " 0.2
0.1233 0.1237 5 * 0.3
Table II
Visual Titration In Cold 0,8 M HC1 Solution
Gm. T1 Taken Gm. T1 Found & Error
0.00804 0.00900 12.0
0.01608 0.01748 8.8
0.02413 0.02524 4.7
0.03217 0.03290 2.0
0.04825 0.04955 2.7
0.07237 0.07425 2.6
0.09651 0.09852 2.1
0.1206 0.1226 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