[cominghome]

hi, I really need help on this.  How do I figure out the pH of a solution of 0.020 moles of NaOH and 0.010 moles of benzoic acid in a total 1 liter solution?  Here's what I'm trying so far: I found the limiting reactant (the acid) and I'm taking what's left of NaOH and reacting it with water, giving me Na+ and OH- ions.  If I set up an equilibrium constant equation to find the OH- ions, what will I set the K equal to? 

Please explain this out to me clearly if I'm doing it right or what I need to do.  Thanks!

[macman104]

You are very close.  Find the concentration of the remaining OH^- ions.  Then you have two options:

Convert [OH^-] to [H⁺] and find pH.

or

Find pOH and convert to pH.

This is a strong base, so no need for K equations, there really is no equilibrium.

[cominghome]

so basically, the OH- ions will just be what's left of NaOH after the reaction goes to completion? 

[macman104]

Yup!