Easy 10 points! Which of the following would make the best buffer system and why

a) KCL and HCL
b) NaOH and H2O
c) CH3CHOHCOOH and NACH3CHOHCOO
d) NaNO3 and HNO3

The answer here is C. The reason is that a buffer (a solution that resists changes in pH) is most effective when it is made up of a weak acid and its conjugate base or a weak base and its conjugate acid. Each of the answer choices includes a conjugate acid-base pair, but all of them are strong except for c, and strong acids or bases don't make good buffers because, by definition, they create solutions with a lot of H+ or OH- ions in it, which would completely defeat the purpose of having a solution whose pH does not change significantly.

C is definitely the best answer. CH3CHOHCOOH is a weak acid, and CH3CHOHCOO- is its conjugate base (you can ignore the sodium ion because it has no acid-base properties).