Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: IAmLegendToo on April 25, 2009, 10:02:04 PM
-
A 100.0 mL sample of 0.18 M HClO4 is titrated with 0.27 M LiOH. Determine the pH of the solution after the addition of 66.67 mL of LiOH (this is the equivalence point).
Now, if I'm not mistaken, HClO4 is a strong acid and LiOH is a strong base, so at the equivalence point, isn't a strong acid-strong base titration automatically a pH of 7.00? But, answer is said to be 2.76. How is this obtained. I've tried multiple routes and just can not get that answer.
-
pH 7 sounds right to me.
-
Exactly!
But, I'm reviewing old exams studying for my upcoming final, and I got that problem wrong. Professor marked my answer, and many others, of 7.00 wrong. Claims answer is 2.76. I don't see how.
-
Ask him to explain it. Don't see any way it could be anything but 7 +/- 0.00001 units.
-
IF it is equivalence point, pH should be very close to 7.00, even after taking ionic strength of the solution into account, and fact that pKb of LiOH is 0.36.
But funny thing is that if - instead of starting with the information "equivalence point" - you base your calculations literally on the concentrations and volumes given you end with pH of 8.59. That's because 66.67 mL is rounded 66.(6) mL - and so close to the equivalence this small difference (in the range of 0.003mL) in volumes gives that large shift of pH value.