Dissociation

[chiddler]

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If pH is > pKa, then acid is deprotonated.

1. What about pKb?

2. What is the proof for that statement? Meaning why is acid deprotonated when pH > pKa?

 

[MedPR]

If pH is > pKa, then acid is deprotonated.

1. What about pKb?

2. What is the proof for that statement? Meaning why is acid deprotonated when pH > pKa?

I assume pH > pKa means the solution is more basic than the solute so, in an attempt to equilibriate, the solute will protonate all the base around it, thus becoming deprotonated.

If pH > pKb? I think you would have to calculate the pKa and see what the relationship is between pH and pKa.

 

[milski]

The reaction is:

HA <-> H+ + A-

pKa is -log[H+] for the concentration of the acid when the acid/base equilibrium is established. if pH > pKa, the concentration of [H+] is lower than the equilibrium concentration and the reaction will move to the right.

pKb applies to the conjugate base - if pOH > pKb the base will be protonating since [OH] is too low.

Added: If you want a more precies proof, you should consider that Ka=[H][A]/[HA] at equilibrium. But for [HA]>>[H] we have that [A]/[HA] = 1, and Ka = [H] at equilibrium or pKa = pH at equilibrium.

The interesting assumption here is that [HA] >> [H], which is correct most of the time. It is still means that at the extreme cases the above will be incorrect.

 

[chiddler]

Cool thanks for the helpful responses. Well understood now!

This chapter is taking way too long...

 

[MedPR]

Which one is that? Acid/base or buffers?

 

[chiddler]

Which one is that? Acid/base or buffers?

acid/base.

it's not lengthy, i'm just bad at it so i have to inch through everything!

 

[MedPR]

acid/base.

it's not lengthy, i'm just bad at it so i have to inch through everything!

That's how I've been with physics. It's a pain.