Chem question help please!!!

[vik91]

I have no idea how to do this question. I feel comfortable with the henderson equation but just not sure how to use that with this question.

AN ACID HA HAS PKA = 5.3. Calculate pH at which 25% of this acid will be in its basic form (A-)

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[starnova]

pH = pKa + log A-/HA
pH = 5.3 + log (.25/.75)= 4.82
use mols HH equation, but in this one it doesn't matter

 

[HdK]

beat me to it =( or log (1/3). Makes sense cuz becomes a little more acidic as 25% of the acid is being converted into ionic H+