Now that we understand what an acid is, we need a method of quantifying which acids are stronger and which are weaker. pH doesn’t work for this, let me explain why:
Concept #1: Why we use pKa instead of pH.
The Ka (dissociation constant) describes the tendency of a molecule to break apart. In the case of acids, that specifically means donating protons, which is exactly what we are interested in knowing!
Concept #2: The relationship between equilibrium constant and pKa.
Concept #3: The pH scale vs. the pKa scale.
The pH and pKa scales really are completely different. Pardon my French! pKas are obviously something I’m really passionate about.
This is the easiest kind of question you could get. Calculating pKa’s just takes some very simple math.
What is the pKa of acetic acid? Hint: take the negative log of the dissociation constant.
Example #1: Calculate the pKa of acetic acid.
What is the pKa of ammonium? Hint: take the negative log of the dissociation constant.
Example #2: Calculate the pKa of ammonium and determine if it is a stronger acid than acetic acid.