Chapter 6: Chemistry of Water, Chemistry in Water

Water possesses extraordinary physical characteristics that distinguish it from other small molecules, including its unusual density relationship with temperature, exceptional heat capacity that stabilizes global climate, and remarkably high surface tension and boiling point. These distinctive properties arise primarily from hydrogen bonding, a strong type of intermolecular force that occurs between water molecules and other substances containing nitrogen, oxygen, or fluorine. The chapter explores how intermolecular forces—attractions between molecules rather than within them—govern the behavior of molecular substances through three main mechanisms: dispersion forces that increase with molecular polarizability, dipole-dipole interactions between polar molecules, and the particularly significant hydrogen bonding interactions. Water's unparalleled ability to dissolve ionic salts and polar compounds stems from ion-dipole forces that compete with lattice forces holding crystals together, ultimately producing aquated ions surrounded by water molecules. The dissolution process depends on whether substances are strong electrolytes that completely dissociate, weak electrolytes that partially ionize, or non-electrolytes that remain intact, with the general principle that polar solutes prefer polar solvents driven by entropy considerations. Four major categories of inorganic reactions occur in aqueous solutions, each representing competitions between molecular attractions: precipitation reactions where ions form insoluble lattices while spectator ions remain dissolved, redox reactions involving transfer of electrons between species, acid-base reactions where protons transfer according to Brønsted-Lowry principles and water itself undergoes self-ionization, and complexation reactions where ligands bond to metal cations. Finally, the chapter addresses quantifying solutes through molar concentration while stressing the critical distinction between the concentration of added solute and the actual concentration of individual species in solution, particularly important for substances that dissociate or ionize.