I am working on problems such as :
The charges on the side groups at each pH are found by the following rule:
- At $\ce{pH < pK}$ a , ${H+}$ on, protonated
- At $\ce{pH > pK}$, ${H+}$ off, deprotonated
- at $\ce{pH = pKa}$ , neutral
But why can we compare $\ce{pH}$ and $\ce{pKa}$ directly?
I just started my amino acids topic. In all my acid and base questions we always compared $\ce{pH}$ to $\ce{pKa}$ using the Henderson Hasselbalch Equation. So why do we now compare $\ce{pH}$ to $\ce{pKa}$ directly?