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Quick chem question - help!

N

NewSc2

Diamond Member
I have a titration curve in front of me, and I've used MathCAD to calculate out the equivalence points.

I used a 0.1 M NaOH solution to titrate an unknown acid mixture.

I know the equivalence points, and they occur at 23.8mL and 37.2mL. How do I find the pKa from this? I've been reading half equivalence point is where pH = pKa, but do I just look at my curve and estimate what pH is at the half equivalence volume? (11.9mL and 16.6mL?)
 
Originally posted by: NewSc2
I have a titration curve in front of me, and I've used MathCAD to calculate out the equivalence points.

I used a 0.1 M NaOH solution to titrate an unknown acid mixture.

I know the equivalence points, and they occur at 23.8mL and 37.2mL. How do I find the pKa from this? I've been reading half equivalence point is where pH = pKa, but do I just look at my curve and estimate what pH is at the half equivalence volume? (11.9mL and 16.6mL?)
Click to expand...

Woah
 
Minendo already gave you what you need. Molarity x Volume = Molarity x Volume. 3 variables, 1 unknown, 1 equation. Your 2 titration equilibrium points imply that you have an acid like H2S04, if i'm remembering my chem ok. Didn't do any acids like that in General Chem. Last time I saw that was in high school.

Edit: H2SO4 and its ilk are called diprotic acids (2 H+ protons, duh. Can't believe I forgot that).
 
Originally posted by: BigPoppa
As a bump and a reference, This website will be a good reference for you. You prolly have a strong base with a weak acid, instead of a diprotic acid.
Click to expand...

NaOH is a strong base. Extremely strong base as a matter of fact.
 
The "prolly" part was in reference to the weak acid seeing as his titration endpoints are so far apart. But now after rereading his OP, he says equivalence points. Its either a weak acid or a strong/weak diprotic acid.
 
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