In this diploma thesis we measured the density of solutions of different alkali halides and their binary mixturesto examine the volume changes that occur when the solutions are mixed. The mixing of chosen two solutions of diferent salts was carried out with solutions of the same concentration as a function both of the concentration and of the volume ratios between the both solutions. Using accurately measured densities of these volume changes we wanted to verify if the law of matching water affinities can be confirmed with accurate density measurements. Preparation of the measured solutions consisted of weighing and precise determination of solution concentrations with the use of potentiometric titration. The densities of the solutions were determined with the help of an oscillating U-tube density meter at 25 °C. From the measured oscillating times we calculated the densities of solutions; the density meter was calibrated beforehand. Using these densities we calculated the real volumes of the solutions and compared them to the volumes if the solutions were ideal. Deviations from the ideal behavior of the solutions are presented in graphs as a function of the volume ratio of mixing and concentration.
When mixing solutions of two electrolytes containing a common ion, the volume changes were so small that these changes were of the order of magnitude of the experimental errors. The largest volumetric changes were observed in mixing of NaBr and KF solutions of higher concentrations (the largest volumetric change was exactly at the highest, i.e., 4 M solution). Due to the rather similar ionic radii of sodium and potassium ions it is difficult to attribute the validity of the law of matching water affinities from the observed volume change during mixing. Morever, these observed differences may also be due to experimental errors as a result of the interaction of fluoride ions with a glass oscillating tube.
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