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March 3, 2015

March 3, 2015

Posted by **Remy** on Tuesday, November 29, 2011 at 11:01pm.

- Chemistry help!! -
**DrBob222**, Wednesday, November 30, 2011 at 12:07amSurely you mean Ve = volume at the equivalence point.

The Henderson-Hasselbalch equation is

pH = pKa + log(base)/(acid)

If pH = pKa, then log B/A = 0 and B/A = 1

If pH = pKa + 1, then log B/A = 1 and B/A = 10

If pH = pKa -1, then log B/A = -1 and B/A = 0.1

..........HA + OH^- ==> A^- + H2O

initial....1.....0.......0......0

add.............x..............

change.....-x....-x......x.....x

equil.....1-x.....0......x.....x

The three cases above are done this way.

When B/A = 1, then [(x)/(1-x)] = 1

Solve for x and obtain x = 1-x so you are half way to the equivalence point.

When B/A = 10, then [(x)/(1-x)]=10

Solve for x = 0.90909 and that is the fraction to Ve.

When B/A = 0.1, then......

Set up an ICE chart and substitute moles into it for base and acid and use the HH equation to solve for pH for the specific points.

Post your work if you get stuck.

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