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

Question

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.

Work

It's incomplete, but I fulfilled the formula, and got (below)...

Answer result

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Answer 1 · 2017-03-14T20:54:03

#pH=10.23#

( explanation under construction by question owner )

#8.5\times10^(-2)# M NaOCl

#K_a(HClO)=2.9\times10^(-8)#
#K_b(ClO^-)=(1.0\times10^(-14))/(2.9\times10^(-8))#