Determination of Water Hardness by the Interferometric Method
Abstract Generated abstract
The paper describes the use of interferometry for rapid determination of temporary water hardness, motivated by the method’s ability to measure solution concentrations accurately with limited time expenditure. Because the approach requires a constant relative salt composition, measurements were performed on Tom River tap water during the winter period, with hardness values obtained by titration and matched to ITR-1 interferometer readings. The authors prepared harder water by room-temperature evaporation, constructed a calibration curve relating titrimetric hardness to refractive-index-proportional interferometer readings, and propose the resulting procedure for student laboratory practice.
Full Text
DETERMINATION OF WATER HARDNESS BY THE INTERFEROMETRIC METHOD
E. G. Labykina, O. I. Evdokimova, G. A. Elagina
(Recommended by the seminar of the Department of General and Inorganic Chemistry)
The principle of the interferometric method of investigation is described in [1]. It gives accurate results in determining the concentrations of solutions with little expenditure of time. In his time Brodskii [2] pointed out the advisability of applying this method to the determination of water hardness.
Natural water contains various dissolved salts, the relative amounts of which probably change as the season of the year changes. The interferometric method can be applied only in the case of a constant relative composition. Taking this into account, we carried out measurements of water hardness in the winter period, when the relative composition of the salts is preserved.
In tap water, whose source is the Tom River, we determined the content of temporary water hardness by the titration method, simultaneously determining the readings for water samples on an interferometer. Water with an increased hardness content was obtained by evaporating it from a large surface (a thin layer of water in a crystallizer) at room temperature.
On the basis of the data obtained, a calibration curve was constructed (Fig. 1) in coordinates: titrimetrically determined water hardness in mg-eq—reading \(m\) on the ITR-1, where \(m\) is a quantity proportional to the refractive index of the solution (cell 80 mm).
Using the calibration curve, it is possible to determine the temporary hardness of water quickly and accurately.
Fig. 1. Calibration curve for determining the temporary hardness of Tomsk water from interferometer readings (cell 80 mm).
Conclusions
A method has been developed for determining the temporary hardness of water by the interferometric method for use in a laboratory practicum for students.
References
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E. T. Labykina. Application of the interferometric method in studying reaction kinetics. Izv. TPI, 128, 91 (1965).
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A. I. Brodskii. Interferometric method of analysis. Zhurn. Zavod. Labor., 8, 1282 (1936).