I'm confused which values of pka i have to choose and what does mean each one of them. knowing that i have read all your articles about the pka but still I can't make the diffrence between them. I need help please.
This molecule has two groups which are ionizable in aqueous media. One of them is a weak acidic and the other is a weak basic group.
The weak acidic group pKa value is 11.27.
The weak acidic group as Anion and unionized neutral species co-exists at a given pH in aqueous media.
The weak basic group pKa value is 1.12.
The Cationic form of the basic group and its neutral form is in equilibrium at a pH value in the solvent.
The ionization constant (Ka) is governed by the equilibrium ratio of the conjugated basic and the conjugated acidic forms of the equilibrated solution.
Ka = [conjugated base ][H+]/[conjugated acid]
On the attached figure (fig1.) the main ionization steps are depicted.
The pH-distribution of the different species is sketched on the fig2. In a wide pH range (2-10) the dominant molecular form is the neutral one. This is in agreement with the weak acid - weak basic character of the molecule.
My compound have acidic and basic pka it means that it acts like acid when the PH value > acidic pka value=11.27 ,it acts like basic when the PH value < basic pka value=1.12 and like neutral in the PH rang of [1.12-11.27].
I have an other compound with tow basic pka values and one acidic pka value. But when I see the pH-distribution of this different species one of the basic pka is almost zero. It mean that my compound have just tow values of pka.
I have an other compound with tow basic pka values and one acidic pka value. But when I see the pH-distribution of this different species one of the basic pka is almost zero. It mean
that my compound have just tow values of pka.
The molecule has two basic groups and one acidic group, therefore, this molecule has 3 pKa values.
One of the two basic groups is very weak. This group will be ionized at low pH value. The pKa = 0.0 means that this group is ionized in 50% degree at pH = 0.0.
This weak basic group will be unionized up to 100% at pH >2 (approximately).
The degree of the ionization of the other stronger basic group and the acidic group will depend on the pH and their pKa values.