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May 26, 2015

Homework Help: CHEMISTRY

Posted by Alexander on Thursday, November 10, 2011 at 4:57pm.

Strong base is dissolved in 675 ml of 0.200 m weak acid (ka=3.25x10^-5) to make a buffer with a ph of 3.95. Assume that the volume remains constant when the base is added.
HA + OH ---> H2O + A^-

calculate the pka value of the acid and determine the number of moles of acid initially present
-so i got pka=4.488 and 0.135 mol HA

When the reaction is complete , what is the concentration ratio of conjugate base to acid.
i got [A^-]/[HA]=0.2897
bob said it was something around 0.117 but i dont get that ..
3.95-4.488=-0.538
10^-0.538=0.2897


Then it says , How many moles of strong base were initially added?... All i know the strong base has to be less than the number of moles of acid but i have no clue how to get the moles of OH^-.

Can you guys help me? Thank you so much!
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