Dynamic Method for the Determination of Hygroscopicity of Water-Soluble Solids
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Dynamic Method for the Determination of Hygroscopicity of Water‑Soluble Solids Anatoly G. Tereshchenko1 Received: 12 November 2019 / Accepted: 20 May 2020 / Published online: 18 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This article presents an extensive examination of a variant of the dynamic method for determining hygroscopic points of pure soluble substances (relative air humidity over the substance’s saturated solution), in which equal amounts of the investigated substance and the reference substance are held in identical sample cups in a sealed chamber for the time that is long enough to change the samples’ mass by 0.05–0.15 g. Examples of the experiment procedures aimed at determining the water vapor absorption/desorption rate coefficient and hygroscopic points values are provided. The effects of the driving force behind the hygroscopic process, relative humidity, cup’s shape, fill level of cups, and chamber volume on the kinetics of samples’ mass changes in the chamber are considered. The experiment technique is organized in such a way that the influence of ambient air is offset in calculations. The method does not require any special laboratory equipment, has a simple implementation technique, and yields the determination results with the reasonable uncertainty that is sufficient for practical purposes. Keywords Determination of hygroscopic points · Dynamic method · Hygroscopicity · Deliquescence · Potassium nitrate
1 Introduction Chemists have synthesized millions of chemicals, a significant part of which are watersoluble solids. Tens of thousands of them are applied in industry and in scientific research. Data on the solubility of these substances in water are widely known and summarized in multivolume reference books [1–6]. All these solubles can deliquesce not only in liquid water, but also in water absorbed from humid air, i.e. they are characterized by a certain degree of hygroscopicity. Solubility reference books are constantly published and edited but is there at least one specialized reference book on hygroscopicity? There have been attempts to generalize literature data on water vapor sorption isotherms [7] and hygroscopic points [8–11], but they provide information for several hundred substances only.
* Anatoly G. Tereshchenko [email protected] 1
National Research Tomsk Polytechnic University (TPU), 30 Lenin Ave, Tomsk 634050, Russia
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1030
Journal of Solution Chemistry (2020) 49:1029–1051
Meanwhile, chemical reference books, encyclopedias, articles on the physicochemical properties of substances, as a rule, do not provide quantitative thermodynamic characteristics of hygroscopic properties even for those solubles for which they have long been wellknown. In the best case, we can find a qualitative evaluation like “hygroscopic”, “highly hygroscopic”, or “not hygroscopic”. Yet, quantitative information on substances’ hygroscopicity is necessary in everyday life, in cooking, in medicine, in agriculture, in chemical technol
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