Titration curves have always confused me. I was introduced to them as a freshman in college. I didn’t really understand the whole concept of conjugate base and an acid and how they related. I didn’t understand what pKa or Ka meant but now I think after taking upper level courses the relationship between pKa, pH, acids, and conjugate bases all finally makes sense. On a titration curve there are inflection points, this point represents the amount of base required to react one half of the desired acid. At this point the acid becomes half deprotonated and half protonated. Next is the equivalence point, the point that represents the amount of base to react with all of the desired acid. This now makes sense to me why the acid is noted as HA and the conjugate base is noted as A-. The acid (HA) is neutral and when it becomes deprotonated taking on its conjugate base form (A-) it loses a proton and now has a net negative charge. This is how I started to understand the relationship between pKa and pH. Again, at the inflection point the amount of conjugate base is equal to the amount of acid. When you plug this ratio into the Henderson-Hasselbalch equation you get pH=pKa+log(1), log(1)=0. So that means that pH=pKa. Which now makes sense why stronger acids have a lower pKa. It essentially means that they are more will to give up a proton at a lower pH.
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