[Greg86]

Hi! Is it possible to reliably calculate the amount of 25% ammonia needed to change the pH of 0.08M 2-hydroxyisobutyric acid to 4.6? I found that Ka of this acid is 1.22·10^-4

[Borek]

Is it possible to reliably calculate

A lot depends on what you mean by "reliably".

[Greg86]

What I mean is when you start adding ammonia acid dissociates more and how do you describe it mathematically? If it was strong base or acid fully dissociated than no problem but in this case how can you calculate?

[AWK]

You will get a buffer solution. It can be calculated using the Henderson-Hasselbalch equation. Some data are missing, namely the density of ammonia and the volume of buffer solution. But calculation will be unreliable because you have two experimental numbers with one significant digit.

[Greg86]

Molar concentration of the ammonia is 13.3. The solution volume is 250 mL

[AWK]

For 100 L of buffer?

[Greg86]

I want to have 250 ml of hydroxyisobutyric acid of pH 4.6

[AWK]

Then volume of ammonia will be probably below 1 mL.

[Borek]

What I mean is when you start adding ammonia acid dissociates more and how do you describe it mathematically? If it was strong base or acid fully dissociated than no problem but in this case how can you calculate?

General case of pH calculation explained (actually - every equilibrium calculations).