General Chemistry: Acids, Bases, and Equilibrium
The C/P section tests general chemistry heavily in biological contexts. Acids and bases: the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]), relates pH, pKa, and the ratio of deprotonated to protonated acid. When pH = pKa, the concentrations are equal. Buffers resist pH changes when acid or base is added — the most effective buffering range is pH = pKa ± 1. Le Chatelier's principle governs equilibrium: if a stress (concentration, temperature, pressure) is applied to a system at equilibrium, the system shifts to partially counteract the stress. For the equilibrium constant Keq, if Keq >> 1, products are favored; if Keq << 1, reactants are favored. Temperature increases Keq for endothermic reactions and decreases it for exothermic reactions.