PKa

[nageshiict]

How can we calculate pKa of a perticuler compound?

[Markus Laeubli, Metrohm]

According to my knowledge, there is no way of just calculating it.
You may determine it by titration.
It is the pH where the protonated and the deprotoneted form have the same concentration.

[tom jupille]

There is a moderately large compilation of pKa values:
http://research.chem.psu.edu/brpgroup/p ... lation.pdf

[MHD]

According to my knowledge, there is no way of just calculating it.
You may determine it by titration.
It is the pH where the protonated and the deprotoneted form have the same concentration.

Hi Friend,
which kind of electrode can be used to determine pKa, could you please explan the test method in detail?
Thanks a lot!

[Markus Laeubli, Metrohm]

I am not really a titration specialist. But I try to give a answer anyway.

The selection of the electrode depends on the compound you need to test.

But the titration of acids is usually performed with a pH-glass electrode.

Procedure:

- Disolve the compound of interest in water or water/organic solvent.
- Titrate with diluted base (e.g. NaOH)

For a compound with one acid proton, take the pH at half of the volume required to reach the endpoint as the pKa.
For components with more than one acid protones: If there are multiple endpoints you may use the pH in the middle of two endpoints as the respective pKa.

This procedure does not give you the perfect and thoretical pKa but is a quite good approximation.

For more background ask a Titration specialist.

[MHD]

I am not really a titration specialist. But I try to give a answer anyway.

The selection of the electrode depends on the compound you need to test.

But the titration of acids is usually performed with a pH-glass electrode.

Procedure:

- Disolve the compound of interest in water or water/organic solvent.
- Titrate with diluted base (e.g. NaOH)

For a compound with one acid proton, take the pH at half of the volume required to reach the endpoint as the pKa.
For components with more than one acid protones: If there are multiple endpoints you may use the pH in the middle of two endpoints as the respective pKa.

This procedure does not give you the perfect and thoretical pKa but is a quite good approximation.

For more background ask a Titration specialist.

Anyway, thanks!

[nageshiict]

Thank you to all for giving good suggitions