First step is to write the reaction:
C7H5O2H(aq) + H2O (l) → C7H5O2- (aq)+ H3O+ (aq)
Benzoic acid (C7H6O2) is a weak acid whose Ka is 6.5 x 10-5. If 0.490 g of benzoic acid are dissolved in 250 ml of water what mass of sodium benzoate (NaC7H5O2) would need to be added to adjust the pH of of the solution to 5.20? (You may assume that the added sodium benzoate doesn't significantly change the solution volume).
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