[Oxostudent2020]

I'm looking for some help with a titration question -

If you have a titration chart with pH on the y axis and volume on the x axis. Can you calculate the Ka from the chart?

That is Ka = [H+][A-]/[HA]. If you have the pH you can calculate the AH at the starting point of the curve but can you use the pH at a point on the curve to find the [H+] and then from that calculate the [H-] to substitute into the equation?. WHen I do it I end up with some values in excess of 10^-14 and I'm not sure that's correct. The acid is unknown and not requied from what I can tell.

Example -
HA = 10^-3 (pH = 1 from chart)
H+ = 10^-4 (pH = 2 from chart)
A- = 10^-10 (10^-14 - H+)

Substituting back into the formula you can derive a Ka value. The question is, is this theoretically correct or am I completly wrong?

Thanks to anyone who can help.

[Oxostudent2020]

I just noticed a couple of typos in my question so here it is again with them fixed. Any help with this would be greatly appreciated -

If you have a titration chart with pH on the y axis and volume on the x axis. Can you calculate the Ka from the chart?

That is Ka = [H+][A-]/[HA]. If you have the pH you can calculate the AH at the starting point of the curve but can you use the pH at a point on the curve to find the [H+] and then from that calculate the [H-] to substitute into the equation?. WHen I do it I end up with some values in excess of 10^-14 and I'm not sure that's correct. The acid is unknown and not requied from what I can tell.

Example -
HA = 10^-3 (pH = 3 from chart)
H+ = 10^-4 (pH = 4 from chart)
A- = 10^-10 (10^-14 - H+)

Therefore - Ka = (10^-4) x (10^-14 - 10^-4 ) / (10^-3) = 1 x 10^-8

Substituting back into the formula you can derive a Ka value. The question is, is this theoretically correct or am I completly wrong?

[Borek]

HA = 10^-3 (pH = 3 from chart)

Why 10^-3?

H+ = 10^-4 (pH = 4 from chart)

OK

A- = 10^-10 (10^-14 - H+)

Once again - why?

Think: when acid is 50% neutralized, what is ratio of [A^-]/[HA]?

Can you find that point on the titration curve?