Use of the label of bottled mineral waters: a way to introduce the properties of electrolytic solutions

In previous contributions we showed how several subjects related to the chemistry of electrolytic solutions may be introduced in a General Chemistry course considering the analytical and physicochemical data reported on the label of bottled mineral waters. This way is particularly interesting to our students because it considers the real solutions that make possible the maintenance of life on earth. Examples such as the principle of electroneutrality of electrolytic solutions, the relationship between the ratio [HCO3-]/[CO2(aq)] and the pH of the solution, the colligative properties (osmotic pressure and depression of the freezing point) and the concept of “water hardness” were considered. We suggested that it could also be possible to investigate the relationships between the nature and concentration of the ions and the electrical conductivity of the mineral waters. In this contribution we complete our approaches showing firstly how the principle of electroneutrality of the solutions can also be used to confirm that in mineral waters solutions silica is essentially present as H4SiO4 (or as amorphous SiO2) species and secondly how the comparison between experimental and calculated electrical conductivity (at infinite diluition) of the mineral water solutions can be used at the General Chemistry level to introduce the concepts of ionic force and of non ideal behaviour of the solutions. This approach represents in our opinion both a direct way to introduce a difficult topic and a good introduction to the more advanced approaches to the study of electrolytic solutions presented at the more advanced Analytical and Physical Chemistry courses.