How do buffer solutions resist changes in pH?

This is for a chemistry take-home test that I have to complete over the summer. I learned in chemistry class last year that buffers resisted changes in pH, but I never really understood how. The choices for the test are:



a. by releasing H+ in acid solutions

b. by releasing H+ in basic solutions

c. by releasing OH- in basic solutions

d. by combining with OH- in acidic solutions

e. by combining with H+ in basic solutionsHow do buffer solutions resist changes in pH?
It's a very icely posed question. Made me think as well.



What's a buffer? It's a mix of a weak acid-weak base conjugate.



It's like CH3COOH + CH3COONa mixture. Suppose we add acid to the solution, the acid will react with the salt and give acetic acid, thus protons being eliminated from acidic solution through combining.



Is it any one of the options? No!



Suppose we add base to the solution. It will react with the acetic acid and extract H+ from it. This is the release of H+ in basic solution. Is it there in the options? Yes. Then THAT is the answer!