What is the ratio of the molar concentrations of acetic acid to sodium acetate ([acetic acid]/ [sodium acetate]) required to prepare a buffer solution with a pH value equal to 4.5.

Solution:

pH = pKa + log ([sodium acetate]/ [acetic acid])

pKa = -log Ka

Assuming that the acid dissociation (Ka) value for acetic acid is 1.75 × 10^-5 at 25 ºC.

pKa = - log (1.75 × 10^-5) = 4.76

4.5 = 4.76 + log ([sodium acetate]/ [acetic acid])

log ([sodium acetate]/ [acetic acid]) = 4.5 - 4.76 = -0.26

[sodium acetate]/ [acetic acid] = 10^-0.26 = 0.55

[acetic acid]/ [sodium acetate] = 1/ 0.55 = 1.82

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