How do you determine pKa?
Let’s do a general case.
pKa is defined as -log10 Ka where Ka = [H+][A-] / [HA].
This tells us that when the pH = pKa then log [HA] / [A-] = 0 therefore [HA] = [A-] ie equal amounts of the two forms.
If we make the solution more acidic, ie lower the pH, then pH < pKa and log [HA] / [A-] has to be > 0 so [HA] > [A-]..
What does high pKa mean?
The lower the pKa of a Bronsted acid, the more easily it gives up its proton. The higher the pKa of a Bronsted acid, the more tightly the proton is held, and the less easily the proton is given up. Figure AB9. … pKa can sometimes be so low that it is a negative number! High pKa means a proton is held tightly.
What pKa is a strong acid?
Definition of Strong Acids More precisely, the acid must be stronger in aqueous solution than a hydronium ion (H+), so strong acids have a pKa < -1.74.
What is the pKa of ether?
pKa Values for Organic and Inorganic Bronsted Acids at 25 oCNamepKaAcetone conjugate acid-7Benzenesulfonic acid-6.5Acetic acid conjugate acid-6Diethyl ether conjugate acid-3.550 more rows
What is the pKa of an alkane?
alkanes (sp3 C-H), pKa ~ 62. alkenes (sp2 C-H), pKa ~ 45. alkynes (sp C-H), pKa ~ 26.
Does higher pKa mean stronger acid?
Generally. The pKa essentially tells you how much of the acid will actually dissociate. If the pKa is low, then more of the acid will dissociate, representative of a stronger acid.
Is high pKa acidic or basic?
A larger pKa for the conjugate acid indicates a stronger base. For indicating base strength directly we use pKb, in which case a smaller value is more basic.
Does higher pKa mean weaker acid?
All we can say is that a higher pKa implies (as Guy said) a weaker acid, and that the conjugate base of that acid would be correspondingly stronger (not that the substance itself would be a stronger base).
Does high pKa mean low pH?
The lower the pH, the higher the concentration of hydrogen ions [H+]. The lower the pKa, the stronger the acid and the greater its ability to donate protons. pH depends on the concentration of the solution. This is important because it means a weak acid could actually have a lower pH than a diluted strong acid.
What does pKa depend on?
The strength of the acid (pKa) depends on the stability of the base. When the proton leaves the acid, it leaves behind its electrons. Those are super negative, and there is a big negative charge on the conjugate base. You know that if there is a concentrated negative charge, the base is not very stable.