Buffers

[MDwannabe7]

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I know that buffers are made of weak acids/bases and their conjugate salts. If a buffer is a weak acid, conjugate salt solution, does it buffer an acid or base solution? Conversely, if a buffer is a weak base, conjugate salt solution, will it buffer an acid or base? Why wouldn't a buffer work the same whether it's an acid or base that's added?

 

[macmini]

Ok the solution to your question has to do with pKa of a buffer. A buffer works best in close range when pKa=pH. Look at the at a titration curve of a buffer it will have a nice flat range at the pH that it can buffer at. 1st when pH=pKa you will recall that 1/2 of the molecules are in thier conjugate base and conjugate acid form. When acid is added the buffer will act as a base and pick up extra H+ ions and buffer the solution untill a critical mass is reached and it will no longer buffer the solution and cause the pH to rise quickly. The opposite occures with adding a base. The longer the flat area is the better the buffer is.

 

[MDwannabe7]

Ok the solution to your question has to do with pKa of a buffer. A buffer works best in close range when pKa=pH. Look at the at a titration curve of a buffer it will have a nice flat range at the pH that it can buffer at. 1st when pH=pKa you will recall that 1/2 of the molecules are in thier conjugate base and conjugate acid form. When acid is added the buffer will act as a base and pick up extra H+ ions and buffer the solution untill a critical mass is reached and it will no longer buffer the solution and cause the pH to rise quickly. The opposite occures with adding a base. The longer the flat area is the better the buffer is.

So are you saying that a buffer of a weak acid and it's conjugate salt is more likely to buffer an acid since the pH and pKa would be close?

 

[Lukkie]

itll buffer both equally. the pka = pH at the half equivalence point. at this point, you can add the largest amount of base OR acid with the smallest change in pH.

 

[w8ting2exhale]

So are you saying that a buffer of a weak acid and it's conjugate salt is more likely to buffer an acid since the pH and pKa would be close?

buffers must be prepared and carefully chosen according to the pH of what you're planning to buffer. So effective buffers are those whose pKas are close to the pH of your solution.