Buffer capacity of a polybasic acid

For tribasic acids, such as citric acid, the equation is = 2.303 

The same equations apply to weak bases and their conjugate acids. Values of p are additive for mixtures of buffers. 

The pH of a solution of a 1 1 salt of a weak acid and a weak base is given by 

Curves for O.IM sodium hydrogen maleate (pK 5.94) and Tris (pK 8.14) singly and in admixture. 

The greatest value of for such a salt is reached when pATi and pK2 are equal. Values for a O.lM solution are 0.115, 0.038, 0.0045 and 0.0047 for differences between pATi and pA 2 of 2, 4 and 6 pH units respectively. 

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