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1. The ionic strength is maintained constant in all
experiments, since we always work with an excess of
NaCl. Thus, all the pH measures suffer similar effects.
2. Because the
pKa values we obtain are very
similar to those obtained from the literature, and only for this
reason, we wrote that "It is not necessary, therefore, to
standardize the solutions". Of course, working with
titrated NaOH will improve this agreement.
3. We think that the plot of
1/x versus 1/B helps to visualize the consistency of data, and usually a
quadratic minimization with several points linearly distributed
(r > .99) gets better results than averaging.
The determination of the neutralization equivalent
by titration is a very instructive and classical
experimental procedure, but our objective with this paper entitled
"Determination of the Dissociation Constant for a
Monoprotic Acid by Simple pH Measurements" was only to show a
very elemental method for the
pKa determination.
4. Unequal weighting of the points, due to the use
of reciprocals, is an interesting question that would
deserve careful consideration. As for the deviating points, they
can be easily detected as "out of line" in the proposed plot.
5. We think that the results obtained with the
acids tested in this work guarantee sufficiently the reliability
of the proposed method. However, if we want greater
accuracy in the pKa determination, it would be advisable to use
standardized solutions and an accurate value for the
molecular weight of acid.
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