Pharmaceutics Figure 3

Linear Plot of Species versus pH - Monoprotic acids

Monoprotic acids, such as acetic or salicylic acid, have one pKa value and thus two species at various pH values. These forms are the free acid form, HA, and the salt form, A^-. The concentration of each species can be calculated with the equations.

Equation 1 Fraction present as HA

Equation 2 Fraction present as A^-

Some Examples

Acid pKa₁

Acetic^* 4.76

Boric 9.24

Lactic 3.86

Salicylic 2.97

^*Default for Graph above.

References

Martin, A.N., Swarbrick, J. and Cammarata, A. 1970 Physical Pharmacy, 2nd Edition, Chapter 9 Ionic Equilbria, Tabel 9-1, Lea & Febiger, Philadelphia, PA

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Acid	pKa₁
Acetic^*	4.76
Boric	9.24
Lactic	3.86
Salicylic	2.97