For the reaction o-toluidine hydrochloride salt + 10M NaOH --> o-toluidine + NaC

Question

For the reaction o-toluidine hydrochloride salt + 10M NaOH --> o-toluidine + NaCl + H2O, how do you calculate the pH value required to obtain 99% amine form? I believe the questions refers to the o-toluidine form (-NH2), as I am supposed to do this calculation to find the pH required to recover 99% of o-toluidine when adding NaOH to o-toluidine hydrochloride. Formula I will use is pH = pKa + [A-/HA]. Would like to verify the value of 6.44 I am getting. Should it not be higher? update: thanks for the comments so far, looks I need to get more info on my end to clarify the question.

Explanation / Answer

pH calculation,

with 99% toluidine formed,

we would have 1% amine.HCl salt still left in solution

So using,

pH = pKa + log(base/acid)

pKa = 4.44

So,

pH = 4.44 + log(99/1)

     = 6.44

Thus, we would need a pH of 6.44 to recover 99% of amine from the solution.

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