Buffered Solutions - A solution that can resist a change in pH when an acid, H+, or base, OH-, is added

Typical Buffers Usually acid/c.base or c.acid/base Examples: HC2H3O2/NaC2H3O2 or NH4Cl/NH3 Buffers can be made to achieve any pH.

HC2H3O2 (aq)  H+ (aq) + C2H3O2 1- (aq) Calculate the pH of a 0.50 M HC2H3O2/0.50 M NaC2H3O2 solution. Ka = 1.8 x 10 -5 Major species: HC2H3O2 (aq)  H+ (aq) + C2H3O2 1- (aq) I 0.50 M 0 0.50 M C -X +X +X E 0.50 – X X 0.50 + X Assume X’s = 0, and solve Notice when the [acid]=[base], then pH = pKa HC2H3O2, Na+, C2H3O2 1-, H2O = 1.8 x 10 -5

Buffers made easy Henderson-Hasselbalch equation Used for buffer solutions Same problem = 4.74

Now with the addition 0.010 mol NaOH to 1 L of 0.50 M HC2H3O2/NaC2H3O2 ms: HC2H3O2, Na+, OH-, C2H3O2 1-, H2O Mixing an acid, HC2H3O2, with OH- HC2H3O2 (aq) + OH-  C2H3O2 1- (aq) + H2O (l) I.C.E. must be in MOLES I. 0.50 mol 0.010 mol 0.50 mol C. -0.010 -0.010 +0.010 E. 0.49 0 0.51 = 4.74 + log(.51/.49) = 4.76