Acid Base Equilibria

Content

● Acid dissociation constants, Ka and the use of pKa

● Base dissociation constants, Kb and the use of pKb

● The ionic product of water, Kw

● pH: choice of pH indicators

● Buffer solutions

Learning Outcomes

Candidates should be able to:

(a) explain qualitatively the differences in behaviour between strong and weak acids and bases in terms of the extent of dissociation

(b) explain the terms pH; Ka ; pKa ; Kb ; pKb ; Kw and apply them in calculations, including the relationship

Kw =KaKb

(c) calculate [H+ (aq)] and pH values for strong acids, weak monobasic (monoprotic) acids, strong bases, and weak monoacidic bases [Calculations involving weak acids/bases will not require solving of quadratic equations]

(d) describe the changes in pH during acid-base titrations and explain these changes in terms of the strengths of the acids and bases

(e) explain the choice of suitable indicators for acid-base titrations, given appropriate data

(f) (i) explain how buffer solutions control pH

(ii) describe and explain their uses, including the role of H2CO3 /HCO3– in controlling pH in blood

(g) calculate the pH of buffer solutions, given appropriate data