We are being asked to determine the [H3O+] and pH of a 0.200 M solution of benzoic acid.
The equilibrium reaction is (the Ka of benzoic acid can be found in books or online):
C6H5COOH(aq) + H2O(l) ⇌ C6H5COO–(aq) + H3O+(aq) Ka = 6.3 × 10–5
Since C6H5COOH has a small Ka value, it is a weak acid. We need to construct an ICE chart.
What is the [H3O+] and pH of 0.200 M solution of benzoic acid, C7H6O2? The Ka value for benzoic acid is 6.3 x 10–5.
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