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July 25, 2014

Homework Help: chemistry

Posted by craig on Sunday, July 8, 2012 at 10:22pm.

Strong base is dissolved in 665 mL of 0.400 M weak acid (Ka = 3.69 10-5) to make a buffer with a pH of 3.94. Assume that the volume remains constant when the base is added.
HA(aq) + OH-(aq) -> H2O(l) + A-(aq)
Calculate the pKa value of the acid and determine the number of moles of acid initially present.

I got 4.43 for pKa. And 0.266 for moles HA.

When the reaction is complete, what is the concentration ratio of conjugate base to acid?

I got 0.32 for the concentration.

How many moles of strong base were initially added?

This part I keep getting 0.128 but it keeps telling me it is wrong. Please help

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