Calculate the pH of the following solutions: 0.100 moles of HF and 0.200 moles o
ID: 824794 • Letter: C
Question
Calculate the pH of the following solutions:
0.100 moles of HF and 0.200 moles of NaCN in 1.00 liter solution.
(This is a little bit tricky, because here you are mixing a weak acid with a weak base! This is not a
common situation that we have encountered before. Can you write the Bronsted-Lowry acid-base
reaction between this weak acid and this weak base? Can you calculate the value of the equilibrium
constant for this reaction? What can you conclude about this reaction based on the numerical value
(or size!) of the equilibrium constant? You should see that you can essentially run this reaction to
completion! After this reaction is complete, can you calculate the pH of the resulting solution?
Hint: Is there a buffer?)
Show all work for points...!
Explanation / Answer
weak acid weak base forms buffer solution...
pH = pKa + log [salt]/[acid]
HF +NaCN----------> NaF +HCN
0.1 0.2 0 0 intial
0 0.1 0.1 0.1
HF -- pKa = 3.15
pH = pKa + log [salt]/[acid]
= 3.15 +log{0.1/0.1}
pH= 3.15
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.