Problem: The Ka for benzoic acid is 6.5 x 10 -5. Calculate the pH of a 0.10 M benzoic acid solution

FREE Expert Solution

We’re being asked to calculate the pH of a 0.10 M aqueous solution of benzoic acid (C7H6O2).


Since C7H6O2 has a low Ka value, it’s a weak acid. Remember that weak acids partially dissociate in water and that acids donate H+ to the base (water in this case). The dissociation of C7H6O2 is as follows:


C7H6O2(aq) + H2O(l)  H3O+(aq) + C7H5O2 (aq); Ka = 6.5 × 10–5


From this, we can construct an ICE table. Remember that liquids are ignored in the ICE table.



The Ka expression for C7H6O2 is:


Ka=productsreactants=[H3O+][C7H5O2-][C7H6O2 ]


Note that each concentration is raised by the stoichiometric coefficient: [C7H6O2 ], [H3O+] and [C7H5O2 ] are raised to 1.


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Problem Details

The Ka for benzoic acid is 6.5 x 10 -5. Calculate the pH of a 0.10 M benzoic acid solution

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