Sapling Week 2 #9

[JaylinWangDis1L]

A monoprotic weak acid, HA , is ionized according to the reaction

HA(aq)+H2O(l)↽−−⇀A−(aq)+H3O+(aq)pKa=3.92

where A− is the conjugate base to HA.
For this weak monoprotic acid, the predominant species present at pH 1.62 is

[Andreas Krumbein 1L]

Its a weak acid so the concentration of [HA] is pretty much guaranteed to be greater than the concentration of the [H₃O⁺], but if the pKa is especially low then you might want to calculate the concentrations of both and compare them. But essentially you're comparing the concentration of the HA (a neutral compound) to the concentration of the H₃O⁺ (a charged compound).

[Margia Adriano 2A]

Hi there! Typically, if the pH at a given time is lower than the pKa, then you will have more protonated species. In this case you will have more HA at this given pH, which has no charge, so the solution will be more neutral at the given pH. The pKa basically tells you what the pH needs to be for the reaction to be at equilibrium, so if the reaction is at a lower pH, then there will be more of the acid at the time. I hope this helps!

[Sebastian2I]

Hi there! Typically, if the pH at a given time is lower than the pKa, then you will have more protonated species. In this case you will have more HA at this given pH, which has no charge, so the solution will be more neutral at the given pH. The pKa basically tells you what the pH needs to be for the reaction to be at equilibrium, so if the reaction is at a lower pH, then there will be more of the acid at the time. I hope this helps!

Is this a rule without exception? Anytime the pKa is greater than the pH we should respond that more of the initial acid is present?

[Margia Adriano 2A]

Is this a rule without exception? Anytime the pKa is greater than the pH we should respond that more of the initial acid is present?

Hi! I believe so, and I don't know of any exceptions, but if I'm wrong please feel free to correct me!