W2-Solutions I

• Solvents are attracted to surface ions, forming a solvation shell around each ion.
• Each ion is surrounded by solvent molecules, a process called solvation or hydration when the solvent is water.
• Ionic solids dissolve in water through a process involving the separation of solute and solvent particles, formation of new interactions, and enthalpy changes.
• The enthalpy change of solution (DHsoln) can be calculated as the sum of the enthalpies of the three processes.
• The enthalpy of solution can be either positive or negative, depending on the energy required to separate the particles and form new interactions.
• Solubility is an equilibrium term describing the maximum amount of a solid that can dissolve in a liquid at a given temperature in dynamic equilibrium with undissolved solid.
• The solubility of solid solutes in liquid solvents generally increases with temperature, while the solubility of gases decreases.
• The common ion effect occurs when the addition of an ion to a solution lowers the concentration of the other ion to maintain the solubility constant.
• Water dissociates into ions in a process called autoprotolysis, with the concentration of hydronium and hydroxide ions influencing the pH of the solution.
• The Lowery-Brønsted theory defines acids as substances that can donate a proton and bases as substances that can accept a proton.
• The pH of a solution is related to the concentration of hydrogen ions through the logarithmic scale of pH.
• Buffer solutions, made from a weak acid or base and its salt, can resist changes in pH upon the addition of acid or base.
• Aspirin has a pKa of 3.5 and a pH of 7.4 in the human body, with a large ratio of [A-]:[HA] indicating a solution that is predominantly the base form of aspirin.
• pH values can be calculated using the equation pH = pKa + log [A-]:[HA].
• References and further reading suggested include "Aulton's Pharmaceutics" and "Physicochemical Principles of Pharmacy."

Test your knowledge on aqueous solutions, solubility, solubility constants, common ion effect, pKw, Ka, Kb, pH, pOH, Henderson-Hasselbalch equation, weak acids and bases, and buffers.