Calculate the pH of a buffer solution obtained by dissolving 0m1 moles of pyridine and 0.2 moles of pyridinium chloride

Question

I need help with my chem quiz and I do not understand how to approach a question like this. Please help.

Answer 1

* * * Assuming 0.1 mol pyridine

 

 

First determine which is the acid and which is the base. You'll also need to find the pKa of the acid if it is not given.  

 

Looking at the structures, you can tell by the protonated Nitrogen on Pyridinium chloride that :

 

BASE: Pyridine

ACID: Pyridinium chloride

 

Wikipedia: pyridinium cation pKa = 5.25

 

Henderson–Hasselbalch equation:

pH = pKa + log (base/acid)

 

pH = 5.25 + log(0.1/0.2)

 

pH = 5.25 + log(0.5)

 

pH = 5.25 - 0.30

 

pH = 4.95