CHAPTER 6 EQUILIBRIA IN SOLUTION Bonding Structure of Water Water is the primary solvent Water has a large permanent dipole Hydrogen bonding constantly tries to organize the structure of water by constraining Salt any ionic compound that does not contain either the hydroxide ion OH or the oxide ion O If Ka is large then reaction comes to equilibrium far to the right lots of products Small Ka lots of reactants small fraction of the HA acid dissociates into H3O Ka 1 acid strong Ka 1 week acid the kinetic motion of the molecules Water can both donate and accept a proton o H2O l H2O l H3O aq OH aq Equilibrium constant Kb 1 x 10 14 Theory of Acid Base Reactions Cations positively charged ions Anions negativetly charged ions All acids release H ions in water Equilibria and Free Energy in Acidic Solutions HA H2O A H3O o HA acid o A conjugate Base o H2O base o H3O conjugate acid o Ka Strong acids are converted to weak conjugate bases Equilibrium is achieved when Q Keq Ka o Q G RT ln Ka pKa log Ka G 2 303 RT Solutions that are Basic Manipulation of pOH and pKa H2O l B aq OH aq BH o H2O acid Weak o B base o OH conjugate base strong o BH conjugate acid B aq Kb BH OH H3O OH 1 x 10 14 Kw pKa logKb Ka x Kb Kw Keq 1 Kw Strong Acid with Strong Base Strong acid dissociates complete in water and a strong base reacts complete to form OH in water Does not involve an equilibrium but rather is a simple process of counting how much H3O or OH is left over after neutralization Strong Base and Weak Acid Weak acid requires analysis of equilibrium behavior of weak acid and its conjugate base Use ICE TABLES Conjugate base will be strong Resulting solution will be basic o Initial Concentration M o Change x o Equilibrium M x Buffer Solutions Technique of building in a defense to limit pH changes by employing a reservoir of a weak acid and a reservoir of the conjugate base of that weak acid Small degree of dissociation of weak acids provides a line of defense against any added H3O by neutralization Weak acid can coexist with its conjugate base pH pKa log A HA o Henderson Hasselbalch Eqution o Provides the opportunity to design the pH of the buffered solution by selecting the acid equilibrium constant and then creating the solution from that acid and the salt of the conjugate base Titration Reactions