V O L U M E 26, N O . 12, D E C E M B E R 1 9 5 4 insoluble material a t 374 and 550 mp into the equatiom used for analyses, it was found that 1% of this sdbstance in a sample causes positive errors of 0.05 and 0.3% in the determination of benzanthrone and dibenzanthronyl, respectively. Since there appears to be some dibenzanthronyl in the residue, the actual errors are probably slightly less than these calculations indicate. The amount of toluene-insoluble material was not ordinarily determined in the routine analysis of crude samples, but these values were included in Table IS’ so that the accuracv of the method could be better evaluated With this factor taken into account, the total accountability for the three samples ranged from 97.2 to 100.275. Although no comparative method of analysis is available, the closeness of the total accountabilities to 100% and the fact that the complete spectra of crude samples are in essential agreement with those predicted from their calculated compositions indicated the absence of any major systematic wror in the proposed method of analysis.
1977
able value and the synthesis of another compound gave ample opportunity for factors other than the quality of the starting material to effect the results. I n addition, the latter method required considerable effort and time and prevented any rapid evaluation of the effect of a given variable in the dibenzanthronyl *synthesis. Use of the spectrophotometric method has eliminated these difficulties. The principal disadvantages of the method are the errors caused by the background absorption of some samples, the necessity of testing each lot of solvent prior to use, and the mechanical difficult’ies of handling concentrated sulfuric acid. On the basis of several months’ experience in this laboratory, however, it is believed that the results obtained outweigh these disadvantages and that the method will find general usefulness in the analysis of mixtures of benzanthrone and 2,2’-dibenzant8hronyl. LITERATURE CITED ( I ) .IXAL. CHEM.,25,365-80 (1953).
DISCUSSION
Prior to the development of the spectrophotometric method of analysis the quality of dibenzanthronyl was evaluated from its melting point or by using it in the synthesis of some compound for which adequate methods of testing were available. The extremely high melting point often rendered the test of question-
(2) (3) (4) (5)
Badische Anilin- & Sodafahrik, Brit. Patent 203,533 (1922). Johnson, J. Y . . and I. G. Farbenind, A.-G., Ihid.,278,047 (1926). Lutringhaus, A., and Neresheimer, H., A m . , 473, 259-89 (1929). Lutringhaus, A., Wolff, H., and Neresheimer, H., U. S. Patent
1,803,399 (1931). (6) Whetsel, K. B., ANAL.CHEY.,25, 1334-7 (195.7). R E C E I V Efor D review February 24, 1984.
Accepted July 15, 1954.
b
Complexometric Titration of Bismuth KUANG LU CHENG D e p a r t m e n t o f Chemistry, University o f Connecticut, Storrs, Conn.
This work had two principal objectives: to investigate the optimum conditions for the titration of bismuth by ethylenediaminetetraacetic acid and to find a suitable indicator for the direct titration. A simple method has been developed in w-hich bismuth can he titrated by ethylenediaminetetraacetic acid at pII 1.5 to 2.0 using potassium iodide as the indizator, with few metals causing interference. Bismuth can he titrated in the presence of large amounts of lead.
S
C€I\V.UtZESBACH ( 4 )described the titration of bismuth by ethylenediaminetetraacetic acid using potnssium iodide as the indicator. However, no detailed investigation as to the conditions of titration and the interference was found in the literature. There is need for a quick and accurate method of determining macro quantities of bismuth. This paper describes a simple and quick method for the direct titration of bismuth by disodium ethylenediaminetetraacetate (Versenate) using potassium iodide as the indicator. The titration is carried out a t pH 1.5 to 2.0 where comparatively few metals form S’ersenate complexes of sufficient strength to cause interference. The proposed proredure will be found particularly useful as no interference was found from relatively large amounts of lead which are always associated with bismuth and difficultly separated. Pfibil and Cuta ( 2 , 3 ) developed an excellent method in which bismuth can be separated conveniently as hydroxide from most metals in the presence of Versenate. When this separation is followed by a romplexometric titration: the result is a rapid and ~ i d e l yapplicable analytical method for bismuth. REAGENTS
Versenate standard solution, 0.01M. Approximately 3.72 grams of disodium dihydrogen ethylenediaminetetraacetic arid were dissolved in water and diluted to 1 liter. This solution was
then standardized against the standard zinc wlution using eriochrome black T as an indicsator ( 1 ) . Standard zinc solution, 0.01M. An accurately weighed sample of 0.6538 gram of pure zinc was dissolved i n 10 ml. of 1 to 1 hydrochloric acid and diluted to 1 liter with nater. Standard bismuth solution 0.01X. Approximately 4 85 grams of bismuth nitrate pentahydrate, were dissolved in 20 ml. of 1 to 1 nitric acid and &luted to 1 liter with water. The Sohtion was standardized against the standard Versenate solution. Potassium iodide solution, 0.570. Five grams of potassium iodide were dissolved in 1 liter of water. This solution should be freshly prepared every day. Sitric acid, 1 to 1solution. Hydroxylamine hydrochloride, C.P. grade. PROCEDURE
Back-Titration with Standard Bismuth Solution. The solution containing 10 to 50 mg. of bismuth in a 250-ml. beaker was diluted to approximately 50 ml. and using a pH meter, was adjusted to pH 1.5 to 2.0 with dilute ammonia or dilute nitric acid. An excess known amount of standard Versenate Rolution was added, then 10 ml. of 0.5% potassium iodide solution were added slowly. The solution was back-titrated with the standard bismuth solution to a distinct yellow rolor. .An indicator blank determination should be made (usually 0.02 to 0.05 ml.). Direct Titration with Standard Versenate. For titrating bismuth in the presence of copper or nickel, direct titration with Versenate is recommended. The solution containing 10 to 50 mg. of bismuth in a 250-ml. beaker was diluted to approximately 50 ml. and adjusted t o pH 1.5 to 2.0. The solution was directly titrated with Versenate after addition of 1 to 2 ml. of potassium iodide indicator. Another 8 to 9 ml. of iodide indicator were added just before reaching the end point, which was from yellow to colorless. The calculation may readily be made according to a 1 to 1 ratio of the bismuth Versenate complex. DISCUSSION
Effect of pH. As PEibil (2)first pointed out, bismuth is still stronply complexed by Versenate a t pH 1. No sharp end point was obtained when the solution was adjusted to pH 1 or below.
ANALYTICAL CHEMISTRY
.I978 It wm also impossible to titrate bismuth at a pH higher than 2.5, at which point bismuth hydroxide was precipitated out. The optimum pH range for the titration was found to be 1.5 to 2.0. When glacial acetic acid (about 10 nil.) was used to adjust the pH-rather than ammonia or nitric acid-more potassium iodide was needed to obtain the end point. Interferences. Foreign cations may interfere by forming stable Versenate complexes or by forming colored or insoluble complexes with the iodide indicator. The following metals did not interfere: sodium, potassium, lithium, calcium, magnesium, barium, strontium, aluminum, lanthanum, chromium(III), manganese(II), copper( II), nickel, copper(I), zinc, cadmium, tin(II), lead uranyl(II), and tungsten(V1) (see Table I). Copper(I1) caused an indistinct end point because i t oxidized the iodide to iodine, but the interference was removed by reducing copper( 11) to copper(I ) with hydroxylamine hydrochloride. The presence of relatively large amounts of copper or nickel resulted in a slow end point in the back-titration procedure, but the direct titration with F-ersenate gave a sharp end point. The following metals interfered: thallium(I), ceriuni(III), iron(III), titanium(III), zirconium, silver( I), mercury(II), molybdenum(T’I), and vanadiuni(V). No interference waa found from the following anions: rhloride, nitrate, sulfate, phosphate, bromide, acetate, and fluoride. A relatively large amount of lead could be tolerated, but 1 gram of lead showed interference due to the precipitation of lead iodide Tlie reaults for determining bismuth in the presence of lead are showi in Table 11. The interference from iron was quantituti\e because the iron h-as also titrated by Versenate. The presence of aluminum caused a slow end point when the back titration procedure was used. For determining bismuth in a mixture of bismuth and aluminum, an excess known amount of T’ersenate solution was ndded, then the mixture was back-titrated with the standard bismuth solution beyond the end point (1 to 2 nil. in excess) and titrated again with the Versenate solution to the end point from yellow to colorless. Effect of Amount of Iodide. Bismuth reacts with iodide to form bismuth iodide, either in the soluble yellow colored form or in the insoluble orange colored forni depending upon the
Table I. Titration of Bismuth in Presence of Foreign Metals Bismuth, Mg.
AhtaI, Added M g . Sone h-one Sone Ba, C a , hlg a n d Sr, 100 mg. each Zn, 100 Cr(III), 100 Co(I1). 100 c u , 10 ?u-i, 10 Cd. 100 31n(II), 100 La, 10 Sn(II), 1 Fe(III), 1 AI, 1
Taken IO.45 20.90 31.30 20.90 20.90 20.90 20.90 20.90 20.90 20.90 20.90 20.90 20.90 20.90 10.45
Found 10.48 20 I90 31.24 20.90 20.90 21 .OG 21 06 20.92 20.96 20.88 20 88 20.90 20.94 24 40 10 2.5
Difference +0.03
+o.oo -0.OG
+o 00
+o.oo
+ O . 16 + O . 16 +0.02 +0.06 -0.02 -0.02 +o, 00 4-0.04 t3.50 -0.20
Table 11. Titration of Bismuth in Presence of Lead Lesd Added, llg.
Taken
50 50 100 100 500
20.90 20.90 20.90 20.90 20.90 20.90
500
Bismuth, SIg. Found Difference 20.90 20.90 20.92 20.88 20.92 20.94
+o +o
00
00 -0.02 -0.02 +0.02 f0.04
amounts of bismuth and iodide present. The iodide did not precipitate bismuth in the presence of Versenate. If the direct titration procedure is used, the amount of iodide added should be kept in such concentration that bismuth will not be precipitated out but will form an intensively yellow color. It was found satisfactory to add 1 or 2 ml. of 0.5% potassium iodide solution to the beginning of the titrat,ion and the rest (8 to 9 ml.) of the iodide solution, before the end point was reached. LITERATURE CITED
(1) Brown, E. G., and Hayes, T. J., Anal. Chim. Acta, 9, 1-5 (1953). (2) Piibil, R., Collection Czechoslov. Chem. Communs., 18, 783 (1953). (3) PIibil, R., and Cuta, J., Ihid., 16, 391 (1951). (4) Schwarzenbach,G., “Komplexon-bIethoden,” Zofingen, Switzerland, B. Siegfried A.G., 1950. R E C E I V Efor I ) review M a r c h 3, lCl54.
Accepted June 2.7, 19.54
Titration of Bismuth with Ethylenediaminetetraacetic Acid JAMES S. FRITZ lowa State College, Ames, lowa
Existing methods for the titrimetric determination of bismuth are subject to numerous interferences. In the proposed method bismuth is titrated directly with disodium ethylenediaminetetraacetate, forming a stable, soluble complex. Excess thiourea is added to form a weak complex with bismuth and thus prevent any precipitation before or during the titration. The disappearance of the last yellow color due to this complex marks the end point. By this procedure bismuth can be accurately titrated in the presence of man) other ions, including large amounts of lead.
A
YALYTICAL methods for the determination of macro amounts of bismuth have for years been almost exclusively gravimetric. Recently, however, several titrimetric methods involving the use of disodium ethylenediamine tetraacetate (Versene) have been proposed. I n 1952 Landgren (3) determined bismuth indirectly, back-titrating the excew Versene with magnesium. I n a similar manner PPibil ( 4 ) back-titmted e x c w
T’ersene with ferric iron a t pH 3 to 5 using either a potentiometric or visual end point. Schwarzenbach (6) and Cheng ( 1 ) have devised methods using iodide as the indicator. Ter Haar and Baain ( 8 ) determined bismuth by adding excess T’erspnp and back-titrating with thorium. PPibil described n direct amperometric titration for small amounts of bismuth ( 5 ) . Gronkvist titrated bismuth directly using a high concentration of thiourea as the indicator ( 2 ) . The latter method is excellent for the determination of bismuth in pharmaceuticals but is subject to interference from numerous metallic ions. Concurrent with the present work, Underwood (9) developed a photometric titration of bismuth with Versene using either the copper ion or thiourea as the indicator. Starting with the method suggested by Gronkvist ( Z ) , a method has been developed for bismuth which retains the simplicity and accuracy of the original but is remarkably selective for bismuth. Bismuth is titrated T+ ith standard Versene forming a soluble, 1 to 1 complex. The titration is carried out a t pH 1.5 to 2.0, Using ahout 0.6 gram of thioiiren as the indic:itor. The end point
