HIGH-FREQUENCY TITRATION. DETERMINATION OF FLUORENECARBOXYLIC, SULFURIC, AND NITRIC ACIDS IN A MIXTURE

V. T. SLYUSARCHUK, A. N. NOVIKOV

(Submitted by the scientific seminar of the departments and laboratories of organic synthesis)

For the quantitative determination of inorganic and organic compounds of acidic character when they are present together, the method of high-frequency titration has been used, based on recording changes in the electrical characteristics of the solution during the titration process [1–4]. This method is being increasingly developed, since it has a number of advantages over other methods of volumetric analysis. It makes it possible to titrate colored solutions, solutions contaminated with precipitating sediments, and emulsions.

Fig. 1. High-frequency direct-titration curve of an aqueous solution of nitric and sulfuric acids with \(0.1N\) KOH

Titration can be carried out in nonaqueous media, as a result of which there is no need to select a suitable indicator [5]. Its accuracy is also counted among its advantages [6].

We carried out titration of a mixture containing fluorenecarboxylic, sulfuric, and nitric acids on a TV-6L1 high-frequency titrator. The equivalence point was determined graphically. On the ordinate axis we plotted the magnitude of the change in voltage across a resistance connected in series with the sensor in the measuring circuit; on the abscissa axis, the consumed volume of titrating reagent.

Into the cell of the instrument we introduced a mixture diluted with water to 70–75 ml, consisting of 0.06 g of fluorenecarboxylic acid, 0.025 ml of nitric acid of \(d\) 1.4, and 0.01 ml of concentrated sulfuric acid. The mineral acids were titrated with 0.1 N aqueous potassium hydroxide solution. Readings on the instrument scale were taken after addition of 0.5 ml of KOH solution. The holding time for taking a reading was 5–10 seconds. On the titration curve (Fig. 1), two inflection points are obtained: the first corresponds to completion of the neutralization of sulfuric acid, the second to nitric acid. From the course of the curve it is evident that, during titration of the acids with KOH solution, the electrical conductivity in the cell decreases, which causes an increase in the resistance used for the measurement.

Fluorenecarboxylic acid was determined by back titration. For this purpose, after neutralization of the nitric and sulfuric acids, an excess of alkali was added in order to convert fluorenecarboxylic acid into the potassium salt. The mixture was left in the cell for 1.5 hours and then titrated with 0.1 N aqueous hydrochloric acid solution. The holding time was 50 seconds. On the titration curve (Fig. 2), two inflection points are obtained: the first corresponds to

Fig. 2. High-frequency back-titration curve of fluorenecarboxylic acid with 0.1 \(N\) HCl

completion of the titration of free KOH, the second to bound potassium hydroxide, which corresponds to a definite amount of fluorenecarboxylic acid. The error of the method does not exceed 1%; it is applicable within the range of electrical conductivity in the cell from \(1 \cdot 10^{-4}\) to \(5 \cdot 10^{-3}\) ohm.

Conclusions

It has been shown that high-frequency titration can be used for the separate determination of sulfuric, nitric, and fluorenecarboxylic acids present in a mixture.

LITERATURE

1. V. A. Zarinskii, I. R. Mandel’berg. Zav. lab., 22, 3, 262 (1956).
2. V. A. Zarinskii, D. I. Koshkin. ZhAKh, 10, 2 (1955).
3. A. G. Shafigullin. Application of Physical Methods in Chemical Kinetics, Tatknigoizdat, 113, 1965.
4. G. Sharlot. Methods of Analytical Chemistry, Khimiya Publishing House, 411, 1966.
5. W. F. Wagner, W. B. Kaufman. Anal. chim., 25, 538 (1953).
6. O. L. Kaptsan. ZhAKh, 8, 8, 131 (1953).