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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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ripple ripple
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11 years ago
Derive an equation similar to equation  pH=pka + log [conjugate base]/[acid] but expressed in terms of f rather than concentrations.

A buffer solution can be prepared by starting with a weak acid,HA , and converting some of the weak acid to its salt (for example, NaA) by titration with a strong base. The fraction of the original acid that is converted to the salt is designated f.

Thank you!  BTW the I can't use HA in my answer.
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#1
11 years ago
HA +NaOH = A- + H2O

f = fraction of original acid = [A-] / [ HA ] + [A-]

Can rewrite it to f /1 = [ A- ] / [ HA ] + [A-]

so [A-] * 1 = f [HA] + f [A-]
[A-] - f [A-] = f [HA]
[A-] (1-f ) = f [HA]
[A-] (1-f ) / f = [HA]
(1-f ) / f = [HA] / [A-]
[A-] / [HA] = f / 1-f

pH = pKa + log [ A-] / [HA]
pH - pKa = log ( f /1  - f )
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