Reactions in aqueous solutions are an important part of chemistry education. As experience shows, they are particularly difficult for students to understand. Hydrolysis is one such reaction. It occurs in organic and inorganic compounds with either covalent and ionic structures, but salt hydrolysis is a special example. Salt hydrolysis is complex, and to understand it, students must consider the reaction equilibrium, dissociation process, and acid-base properties of reactants and products. Additionally, in the upper-secondary-school curriculum, hydrolysis is described only qualitatively, which can lead students to misinterpret hydrolysis and solution equilibrium. In this study, 235 upper-secondary-school students answered questions about the acidity of common salt solutions and tried to justify their responses by writing appropriate chemical equations. An analysis of the answers revealed the students’ alternative conceptions and misconceptions. The character of the misconceptions showed that they are school-based and largely caused by excessive simplification of the process as well as the usage of inappropriate analogies. Key words: salt hydrolysis, acids and bases, alternative and misconceptions, chemical education research.

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Solid polymorphism in five compounds of the type [Me(H20)6](BF4)2 , where Me = Mn, Fe, Co, Ni and Zn, have been studied in the temperature range 120 -330 K by DSC. For each substance at least three solid modifications have been found. In addition, for compounds with Me = Mn, Fe and Zn some new low temperature phase transitions have been observed. The transition temperatures for the [Me(H2O)6](BF4)2 compounds are distinctly lower than those for the [Me(H2O)6](ClO4)2 compounds. The entropy-and enthalpy-changes at the phase transitions of the hexaaquametal(II) tetrafluoroborates are significantly lower than those for the corresponding chlorates(VII). Linear correlations between the highest transition temperature and the crystal density are found for both series of these isomorphous compounds.

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