pKa vs pH

[Quinton Sprague 1A]

Being that Ka is the acidity constant and measures concentration of hydronium ions, I am wondering if pKa is always equal to pH? In the case of a base I guess it would not be likely that you could find the pKa so maybe this is a time where the pH is relied on, but in other circumstances are these two figures equivalent?

[Sophia Hu 1A]

pKa and pH are related, but I believe they are not the same thing and will not always be equal. I believe pKa is constant for the specific molecule because Ka is the acidity constant of that molecule and it is not affected by changes in concentrations. On the other hand, pH is affected by changes in concentrations. I think we can use pKa to determine how the acid, or more generally the molecule, will react within a given pH. This relates to Sapling #9 from Week 2 homework. We use the pKa of the weak acid and compare it to the pH of the solution to determine how the weak acid will react (donate a proton or remain protonated) within the given pH.

I hope this helps!

[Alara Aygen 3K]

I don't think pka equals to pH. pKa is the negative log of the acidity constant, Ka, but I believe they can be used to find out the pH of the solution since pH depends on [H3O+] concentration as well.

[Devan Nathu - 2H]

pKa is the -log of the acidity constant (Ka).