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Buffer Solution Question Help

50 cm^3 of 0.2 mol dm-1 Sodium Hydroxide
Added to same Volume of 0.4 mol dm-1 ethnic acid.
Acid dissociation constant 1.65x10-6.
Find PH.

Note I would rather not do this using the buffer equation but the long way.

I have started by finding the moles of each and got

NaOH= 0.01 Moles
CH3COOH= 0.02 Moles
Therefore we have an excess of acid by= 0.01 moles.
I know now I need to use the equation for the acid dissociation constant but is the concerntation of OH- equal to H+ given that I am just using the excees acid.