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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: zeshkani on October 28, 2007, 03:46:14 PM

Title: quick question
Post by: zeshkani on October 28, 2007, 03:46:14 PM

"A solution is to be buffer at pH = 3:35 with formic acid and formate.
(a) How many moles of formic acid and sodium formate are needed if the solution is to change pH by < 0.02 for the addition of 0.02 moles of strong acid?"

i need help how to set up a problem like this, i dont even know how to approche it !!
it just doesnt make sense to me, iam sure its easy but iam not just understanding it
any help is welcome

Title: Re: quick question
Post by: Borek on October 28, 2007, 06:17:48 PM

First of all - do you know Henderson-Hasselbalch equation (http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch)? Thats your starting point. Plus simple stoichiometry - you may assume that all formate is protonated to formic acid when strong acid is added. That should be enough to set up equations describing the system before and after acid was added. Solve for formic/formate concentration.

Title: Re: quick question
Post by: zeshkani on October 28, 2007, 06:58:54 PM

 :o that was not that hard, thx alot  :)