Respuesta :
The dissociation of formic acid is:
[tex] HCOOH \rightleftharpoons HCOO^{-} + H^{+} [/tex]
The acid dissociation constant of formic acid, [tex] k_a [/tex] is:
[tex] k_a = \frac{[HCOO^{-}] [H^{+}]}{HCOOH} [/tex]
Rearranging the equation:
[tex] \frac{[HCOO^{-}]}{[HCOOH]} = \frac{k_a}{[H_+]} [/tex]
pH = 2.75
[tex] pH = -log[H^{+}] [/tex]
[tex] [H^{+}]= 10^{-2.75} = 1.78 \times 10^{-3} [/tex]
[tex] pk_a = 3.75 [/tex]
[tex] k_a = 10^{-3.75} = 1.78\times 10^{-4} [/tex]
Substituting the values in the equation:
[tex] \frac{[HCOO^{-}]}{[HCOOH]} = \frac{k_a}{[H_+]} [/tex]
[tex] \frac{[HCOO^{-}]}{[HCOOH]} = \frac{1.78\times 10^{-4}}{1.78\times 10^{-3}} [/tex]
Hence, the ratio is [tex] \frac{1}{10} [/tex].
