Please, I couldnt answer this question :

What is the concentration of benzoic acid in an aqueous solution of 0.015 M sodium benzoate? What is the pH of the solution? Ka for benzoic acid is 6.3 x 10-5 M. Answer = [8.19]

Question

Please, I couldnt answer this question :

What is the concentration of benzoic acid in an aqueous solution of 0.015 M sodium benzoate? What is the pH of the solution? Ka for benzoic acid is 6.3 x 10-5 M.			Answer = [8.19]

anonymous · Answer

Henderson-Hasselbalch equation pH=pka+log[salt]/[acid]

anonymous · Answer

So you should know the pH in order to find the conc

anonymous · Answer

Thank you, @Brair  but can you show me how to find the concentration of benzoic acid? 
Thanks a lot

anonymous · Answer

According to the mentioned equation you are not able to find that unless the pH of the buffer is known

anonymous · Answer

Ok2, I'll try. I got pH=8.68 . perhaps I did wrong calculation :) 
TQ

vincent-lyon.fr · Answer

You have to write the reaction between water and benzoate ions.
Look up the paragraph "pH of a weak base" in your book, and you will see how this kind of problem is solved.