Homework Help: chem 126

Posted by carl on Friday, March 15, 2013 at 9:32pm.

Phenolphthalein is a commonly used indicator that is colorless in the acidic form (pH < 8.3) and pink in the basic form (pH > 10.0). It is a weak acid with a pKa of 8.7. What is the ratio of the conjugate base concentration to the acid concentration, that is, [B-]/[HB] when the indicator switches to the acidic color? Hint given in feedback.

chem 126 - DrBob222, Friday, March 15, 2013 at 9:41pm
I don't have the benefit of the "feedback" session but I would use
8.3 = 8.7 + log(b)/(a)
solve for the ratio b/a.
chem 126 - carl, Friday, March 15, 2013 at 9:58pm
i did it i found 0.4 but wrong
chem 126 - DrBob222, Friday, March 15, 2013 at 10:18pm
What was your feedback session?

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