In an aqueous solution of pyruvic acid (CH3-CO-COOH) maintained at a constant pH of 7, what is the ratio of the concentrations of the acid and base species? Data: $ pKa $(pyruvic acid) $ = 2.5 $

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Calculate first $K_a$.

$K_a$ $=$ $10^{-2.5}$ $=$ $3.16\cdot 10^{-3}$

Isolate in $ K_a $ the ratio of the concentrations of acid and base species!

$\frac{[CH_3CO-COO^-][H_3O^+]}{[CH_3CO-COOH]}=K_a$ $\frac{[CH_3CO-COO^-]}{[CH_3CO-COOH]}=\frac{K_a}{[H_3O^+]}$

Calculate this ratio now !

$\frac{[CH_3CO-COO^-]}{[CH_3CO-COOH]}$ $=$ $\frac{3.16\cdot 10^{-3}}{10^{-7}}$ $=$ $3.16\cdot 10^4$