In a #0.70 M# solution of benzoic acid, what percentage of the molecules are ionized (CHEMISTRY 1B problem)?

Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in foods, medications, and personal hygiene products. Benzoic acid dissociates in water:
#C_6H_5COOH⇌C_6H_5COO^−+H^+#
The #pKa# of this reaction is #4.2#. In a #0.70 M# solution of benzoic acid, what percentage of the molecules are ionized?
Express the percentage numerically using two significant figures.


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