Comparing pKa vs. pH and pKb vs. pOH to Determine if Solution is Charged/Neutral

[Kate Anderson-Strain 2D]

Hello!

I was wondering if someone could explain how to tell if the solution is charged or neutral when comparing pKa vs. pH and pKb vs. pOH.

Thank you!

[HoneyWalnutShrimp]

Im going to assume you are asking how to tell if the weak acid/base is gonna be in the charged form not the solution.
For the sake of literacy im going to use a weak acid as an example.

pKa is basically the pH when 50% of the weak acid is in its protonated(uncharged) form and 50% is in its deprotonated(charged)form. Since in this equlibrium equation, the product includes H3O+/H+, placing the weak acid in a solution that is below its pKa (more acidic than the weak acid and thus have more H+) will increase the rate of the reverse reaction and cause the more of the deprotonated anion to become the protonated acid.

I think its easier to think of pKa as the 'ideal pH' that the weak acid/base always wants to be at. To solve these questions think about which direction the protonation/deprotonation reaction would have to go in order for the solution's pH to tend towards the pKa.