achieve #9

[Jenna 1G]

I was wondering if someone can explain to me the relationship between pH and Pka and the neutral or charged acid or base

[Charmaine Ho 2G]

When pH=pKa, there are equal amounts of charged deprotonated A- to neutral HA
When pH<pKa, neutral protonated HA is more predominant = neutral
When pH>pKa, charged A- is predominant = charged

When pH=pKa, there are equal amounts of B and HB+
When pH<pKa, charged, protonated BH+ is predominant = charged
When pH>pKa, neutral weak base B is predominant = neutral

[Stephen_Kim_1D]

There is a general explanation in Achieve, but here's how I like to think of it. pH is -log[H+] while pKa is -log[A-][H+] / [AH] (both expressions have [H+] in them). If pH = pKa, pKa must equal -log[H+]*1; in other words, the fraction [A-]/[HA] in the pKa expression must equal 1, so there are equal concentrations of the charged A- and neutral HA. If the surrounding pH is lower (more acidic) than pKa, [H+] is larger, so [A-] is smaller and [AH] is larger in the pKa expression, and the opposite is true if pH is higher than pKa. So if pH<pKa, there's more neutral AH, and if pH>pKa, there's more charged A-.

[Heba Bounar 3K]

Hi! If you are dealing with an acid and the pH < pKa, then the environment is acidic and the acid is in its neutral form. If the pH>pKa, then the environment is basic and the acid is in its ionized/charged form. If you are dealing with a base and the pH<pKa, then the environment is acidic and the base is in its ionized/charged form. If the pH>pKa, then the environment is basic and the base is in its neutral form. Hope that helps!