Calculate the ph of a buffer solution that contains 0.25 M benzoic acid (c6h5co2h) and 0.15M sodium benzoate (c6h5coona) . Ka=6.5×10-5

4.0

Explanation:

we have a buffer system formed by a weak acid (benzoic acid C₆H₅O₂H) and its conjugate base (benzoate ion C₆H₅O₂⁻, coming from sodium benzoate C₆H₅O₂Na). Given the acid dissociation constant (Ka) for benzoic acid is 6.5 × 10⁻⁵, we can calculate the pH of the buffer solution using the Henderson-Hasselbach equation.

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

pH =-log Ka + log [C₆H₅O₂⁻]/[C₆H₅O₂H]

pH =-log 6.5 × 10⁻⁵ + log (0.15 M/0.25 M) = 4.0