# Conjugate pairs versus not conjugate pairs

1. Mar 13, 2005

### sotellme

to make a 25mM buffer with pH5.2 i add 25mM ethanoic acid with 25mM sodium ethanoate. after adjusting the pH, the buffer will still be 25mM.

will this also be the case if i use 25 mM Tris-base and 25 mM phosphoric acid? will i still get a buffer with 25mM after adjusting the pH to 5.2 with the phosphoric acid?

the first one is a conjugate pair (ethanoic acid and sodium ethanoate), while the second one is not a conjugate pair (Tris-base and phosphoric acid)

thanks.

2. Mar 13, 2005

### GCT

No. You'll need a conjugate pair for a buffer solution, although I'm not sure if your method complies with any other existing ways to make a buffer.

Buffers solutions exists through common ion effect, this is why for the most part the concentration of the conjugates do not undergo equilibrium; I believe that it may be an entropical phenomenon, somebody correct me if I'm mistaken.