Consider the weak organic base n-propylamine. The Kb value for this base is 1.3-10^-5, and its pKa is 10.6. At what pH are the "proton on" and "proton off" forms present in equal concentrations? At what pH values would the "proton on" form have the higher concentration? At what pH values would the "proton off" form have the higher concentration?

Question

DrBob222 · Answer

Use the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid)
(base) is with proton off and (acid) is with proton on.
When (acid) = (base), you see log is 0 and pH = pKa.
Substitute a value for pH and see which ratio (base)/acid or acid/base is higher to get the other parts of the question.