A New Volumetric Method for the Determination of Barium
Abstract Generated abstract
A titrimetric method is described for determining macroquantities of barium in barium salts, addressing limitations of gravimetric and complexometric procedures, especially their duration, reduced accuracy in complex mixtures, and interference from related cations. The method precipitates barium as barium chromate using an excess of standardized potassium dichromate in acetate buffer at pH 4 to 5, then determines the residual dichromate iodometrically after filtration. Tests reported for solutions containing strontium show relative errors generally within about 0.2 to 0.6 percent, with no interference noted from strontium, calcium, magnesium, alkali metals, or ammonium, and an analysis time of 30 to 40 minutes.
Full Text
A NEW VOLUMETRIC METHOD FOR THE DETERMINATION OF BARIUM
Yu. L. Lelchuk, L. A. Shabrova, V. G. Kostylev
(Submitted by the scientific seminar of the Department of Analytical Chemistry)
Many methods are known for the determination of barium [1, 2]. In determining its macroquantities, the most accurate is the gravimetric method, based on precipitating it and weighing it in the form of barium sulfate [2]. However, even this method is not without shortcomings. The determination of barium by this method is interfered with by the cations of strontium, calcium, and lead. The method is lengthy. In determining barium in complex objects, the accuracy of the analysis is significantly reduced because of the phenomenon of coprecipitation [1, 3]. In connection with this, work is still continuing on the search for new, more advanced methods for its determination.
Among works on the determination of macroquantities of barium published in recent years, the greatest interest is presented by the titrimetric method based on the precipitation of barium by sodium thiosulfate in an aqueous-alcoholic medium and titration of the excess thiosulfate with iodine after separation of the precipitate [4], and by complexometric methods [5—10]. However, experimental verification of these methods has shown that all of them have low accuracy; most of them require preliminary separation of barium from strontium and other interfering cations. Complexometric methods are cumbersome.
We have developed a titrimetric method for the determination of barium, based on the precipitation of barium with an excess of a titrated potassium dichromate solution in the presence of an acetate buffer at pH 4—5 and the iodometric determination of the dichromate residue in the filtrate after removal of barium chromate by filtration.
The cations of strontium, calcium, magnesium, alkali metals, and ammonium do not interfere with the determination of barium by this method.
The duration of the analysis is 30—40 min. The relative error of the determination ranges within ±0.2—0.6%.
Experimental Part
All solutions were prepared from reagents of chemically pure or analytically pure grade. The concentration of the initial barium chloride solution was established by the gravimetric method in the form of barium sulfate; the concentration of the thiosulfate solution was established by the iodometric method; the titrated potassium dichromate solution was obtained by dissolving a definite weighed portion of the reagent, purified by recrystallization according to Yu. V. Klimenko.
[11]. An acetate buffer solution with pH 4–5 was prepared by mixing 0.1 N solutions of acetic acid and sodium acetate in equal volumes.
The concentration of the working barium chloride solution was 0.0495 M; strontium nitrate, 0.1 M; potassium dichromate, 0.6 N; sulfuric acid, 2 M; potassium iodide, 20%.
Procedure. To 10 ml of the barium chloride solution being analyzed, 20 ml of the acetate buffer mixture is added and, with vigorous stirring, 5 ml of 0.6 N potassium dichromate solution is added in small portions. The precipitate of barium chromate that forms is filtered off, and the filtrate is quantitatively collected in a titration flask. The precipitate on the filter is washed with water, and the wash waters are combined with the filtrate.
To the filtrate are added 5 ml of sulfuric acid and 5 ml of potassium iodide solution, and the mixture is allowed to stand in a dark place for 10 min. The liberated iodine is then titrated with 0.1 N sodium thiosulfate solution. Starch solution is added at the end of the titration.
The weight content of barium in g-ions/l is calculated by the formula:
\[ \mathrm{Ba}=\frac{V_1N_1 - V_2N_2}{3V_a}\ \text{g-ion/l}, \]
where
\(V_1\) — volume of potassium dichromate solution, ml,
\(N_1\) — normality of the potassium dichromate solution in iodometry,
\(V_2\) — volume of sodium thiosulfate solution used for titration, ml,
\(N_2\) — normality of the sodium thiosulfate solution,
\(V_a\) — volume of the solution analyzed, ml.
The coefficient 3 in the denominator was obtained taking into account that 1 g-mol of potassium dichromate precipitates 2 g-ions of barium and corresponds to 6 gram-oxidizing equivalents in reactions with potassium iodide and sodium thiosulfate.
The experimental data obtained in testing the influence of strontium on the accuracy of barium determination are given in the table.
Table
Influence of strontium on the accuracy of barium determination.
Barium content in all analyzed solutions: 0.0495 g-ion/l
| Added strontium, g-ion/l | \([\mathrm{Ba}^{\bullet\bullet}]:[\mathrm{Sr}^{\bullet\bullet}]\) | Barium found, g-ion/l | Error, absolute, g-ion/l | Error, relative, % |
|---|---|---|---|---|
| 0 | — | 0.0498 | +0.0003 | +0.6 |
| 0 | — | 0.0494 | −0.0001 | −0.2 |
| 0 | — | 0.0494 | −0.0001 | −0.2 |
| 0.01 | 5 : 1 | 0.0494 | −0.0001 | −0.2 |
| 0.02 | 2.5 : 1 | 0.0496 | +0.0001 | +0.2 |
| 0.05 | 1 : 1 | 0.0491 | −0.0004 | −0.8 |
| 0.10 | 1 : 2 | 0.0493 | −0.0002 | −0.4 |
| 0.25 | 1 : 5 | 0.0492 | −0.0003 | −0.6 |
| 0.50 | 1 : 10 | 0.0495 | 0 | 0 |
Conclusions
A volumetric method has been developed for determining barium in barium salts, based on precipitating it with an excess of a titrated potassium dichromate solution in the presence of acetate buffer and on iodometric determination of the remaining dichromate in the filtrate after separation of the barium chromate precipitate.
References
-
G. Charlot. Methods of Analytical Chemistry. Quantitative Analysis of Inorganic Compounds. Khimiya Publishing House, 567, 794, Moscow–Leningrad, 1966.
-
V. F. Hillebrand, G. E. Lundell, G. A. Bright, D. I. Hoffman. Practical Handbook of Inorganic Analysis. Goskhimizdat, 635, Moscow, 1957.
-
V. N. Alekseev. Quantitative Analysis. Goskhimizdat, 110–108, Moscow, 1963.
-
Bosh-Arinyo, Peris-Gomez. Determination of barium by the iodometric method. Referativnyi Zhurnal “Khimiya”, 1957, No. 5, 264, abstract 15648.
-
H. F. Combs, E. L. Grove. Titration of barium with ethylenediaminetetraacetic acid in the presence of other alkaline-earth metals. 36, No. 2, 400 (1964).
-
B. Karadakov, A. Alekseeva. Complexometric determination of barium using sodium sulfate as an indicator. Referativnyi Zhurnal “Khimiya”, No. 16, 12, 1964, abstract 16G7 (Bulg.).
-
Dregushin. Rapid methods for the complexometric determination of barium and sulfates. Rev. Chim. (RPR), 2, No. 2, 110 (1960).
-
V. Golubovic, M. Krastovcevic. Complexometric determination of barium sulfate in gypsum and barite. Referativnyi Zhurnal “Khimiya”, 1964, No. 23, abstract 23G129.
-
G. Charlot. Methods of Analytical Chemistry. Khimiya Publishing House, 568, Moscow–Leningrad, 1966.
-
A. I. Vasyutinskii, V. I. Mogilevskaya. Quantitative determination of barium in the presence of strontium, calcium, and magnesium by means of pyromellitic acid. Journal of Analytical Chemistry, 22, issue 12, 1895 (1967).
-
Yu. V. Karyakin. Pure Chemical Reagents. Goskhimizdat, 174, Moscow, 1947.