Question

Many important biochemicals are organic acids, such as pyruvic acid (pka = 2.50) and lactic acid...

Many important biochemicals are organic acids, such as pyruvic acid (pka = 2.50) and lactic acid (pka = 3.86). The conjugate base are pyruvate and lactate, respectively. Derermine for each acid, which form - the acid or the conjugate base - predominates at pH 7.4.

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Answer #1

We can determine the acid and conjugate base by the following equation

Hendersen's Hassalbalch's equation

pH = pKa + log [salt] / [acid]

a) For pyruvic acid

pH = 7.4 = 2.5 + log [salt] / [acid]

log [salt] / [acid] = 4.9

[salt] / [acid] = 7.94 X 10^4

so here the concentration of salt > acid

So the conjugate base will predominate over acid

b) lactic acid

pH = pKa + log [salt] / [acid] = 7.4 = 3.86 + log[salt / [acid]

3.54 = log [salt] / [acid]

[salt] / [acid] = 3.46 X 10^3

so concentration of salt > concentration of acid

so conjugate base will predominate

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