Ions in Solution ChemConnections（离子在溶液中ChemConnections）.pdfVIP

Adapted from Peer-led Team Learning “Begin at the beginning…and go on till you come to the end: then stop. Lewis Carroll Ions in Solution Early ideas of atoms and compounds, developed primarily through the reactions of solids and gases, did not include the concept of charge. Atoms and molecules were seen as neutral particles. However, as the study of chemistry progressed to include solutions, new models were needed because the old models could not explain electrical conductivity. Studies of the electrical conductivity of solutions, and other properties of solutions such as freezing point depression and osmotic pressure, showed an interesting dichotomy. Solutions of compounds like sugar did not increase the electrical conductivity of water, yet they had lower freezing points than pure water. Solutions of compounds such as sodium chloride greatly affected the electrical conductivity of water, and they also caused the freezing point of the solution to be reduced twice as much as was observed in sugar water solutions. A new model that explained these observations was based on the concept that charged particles, which were called ions, formed in solutions. If compounds like sodium chloride broke apart into charged particles when in solution, the ions could carry electrical current. Substances such as sugar must not break into ions in solution because they did not conduct electricity. These studies of the characteristics of solutions led to a more complete and accurate understanding of chemistry at the particulate level. Solvent and Solute When a solid dissolves in a liquid to form a solution, the solid is called the solute, and the liquid is called the solvent. This is the only case that we will consider in this workshop. Note, these few terms are insufficient to describe solutions in general. They will be expanded