Your choice (acidic) is 

• Note that there are extra protons (H⁺) in the solution.
• Note also that sodium chloride, (NaCl), a bi-product of the reaction, is dissolved in the aqueous solution while the 4-methoxybenzoic acid* has precipitated* out of the solution.

Now you need to collect the benzoic acid. What technique will you use?

Organic Web Chem University of Alberta