Can a 0.1M Buffer Solution Be Prepared Using Henderson-Hasselbalch Equation?

[PhiPhenomenon]

Hey guys,

This question seems pretty easy and straight forward but there's a nagging part of me that isn't sure. I want to say 'no' because I think that the solution goes back to it's acid constant dissociativity levels but I'm not sure.

So the skinny is that someone needs to prepare a 0.1M buffer solution of acid X. One person decides to do so through by adding the proper combination of 0.08 moles of the deprotanated form and 0.02 moles protanted to 1 liter of water form such that it satisfies the Henderson–Hasselbalch equation. That wouldn't work because the acid dissociativity constant dictates that the concentration of protanated an deprotanated forms of acid would change immediately and ultimately satisfy the ka right?

 

[Borek]

Depends on the acid strength. If pKa is higher than about 3.5 this approach will work, for stronger acids it won't for the reasons you are thinking about.