Example pH Titration of Acetic Acid

The function NewtonRaphson.m is very general and can easily be adapted for any titration. The potentiometric titration of acetic acid with NaOH solution serves as an additional example of its usage. 

In aqueous solutions, whenever protonation equilibria are involved, the autoprotolysis of water needs to be incorporated into the model. Thus, for an acetic acid titration the model comprises two equilibria 

The autoprotolysis of water can be included into the algorithm in a very compact way. As already indicated in Table 1, hydroxo species are given the notation H i. According to equation (3.22) we can write  

Thus [H-i]=[OH ] and fioo-i=Kw, the ionic product of water. Refer also to the last column in the Model matrix. 

It is a titration of 10ml of 0.1M solution of acetic acid with 0.1M NaOH. Note the initial concentrations in the lines 

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The function Data EqAH2, m simulates the pH-titration of a weak diprotic acid, AH2, in acid excess, with a strong base. The computation of the equilibria is similar to the examples Eql. m and Eq2. m given in the Chapters Example General 3-Component Titration (p.56) and Example pH Titration of Acetic Acid (p.58). From the present point of view, the important aspect is that all variables are collected in one structure s. The model is now stored in s.Model, the logP values in s. log beta, etc. Importantly, all the information contained in s is returned to the invoking programs. 

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