归东理工大买 Analytical Chemistry 4.Calculation of species present As a strong base neutralizes a diprotic acid,the pH increases and the proportions of H2A,HA,and A2-in solution change.It is useful to know the composition of the solution as a function of pH,can be expressed by graphs of distribution. A good example is in complex-formation reactions, because substances that can form complexes with metal ions usually have acid-base properties. Consider,for example,a monoprotic acid,HA: HA+H,O→H,O+A 20254/6
Analytical Chemistry 2025/4/6 17 4. Calculation of species present As a strong base neutralizes a diprotic acid, the pH increases and the proportions of H2A, HA- , and A2- in solution change. It is useful to know the composition of the solution as a function of pH, can be expressed by graphs of distribution. A good example is in complex-formation reactions, because substances that can form complexes with metal ions usually have acid-base properties. Consider, for example, a monoprotic acid, HA: + − HA + H2 O H3 O + A
G 归东理2大军 Analytical Chemistry The analytical concentration of the monoprotic acid is C=[HA]+[A-] K -HA+) We use SHA to express the fraction HA in the total concentration.The fraction is defined as distribution coefficient. [H] 1+ K。4 [H]+K。 [H] 20254/6
Analytical Chemistry 2025/4/6 18 The analytical concentration of the monoprotic acid is [HA] [A ] − c = + ) [H ] [HA](1 + = + Ka c We use δHA to express the fraction HA in the total concentration. The fraction is defined as distribution coefficient. a Ka c K + = + = = + + + [H ] [H ] [H ] 1 [HA] 1 HA
归东理工大图 Analytical Chemistry The distribution coefficient of A-is [A']Ka [H]+K。 Fraction for various HA species as a function of pH is shown in figure below. δ 1.0 HAc Ac 0.5 ◆ 0.0 4◆ 10 12 pH 4.76 20254/6
Analytical Chemistry 2025/4/6 19 The distribution coefficient of Ais a a K K c + = = + [H ] [A ] - A - Fraction for various HA species as a function of pH is shown in figure below