Selecting proper components for desired pH

Buffers function best when the pKa of the conjugate weak acid used is close to the desired working range of the buffer. This turns out to be the case when the concentrations of the conjugate acid and conjugate base are approximately equal (within about a factor of 10). For example, we know the Ka for hydroflouric acid is 6.6 x 10-4 so its pKa= -log(6.6 x 10-4 ) = 3.18. So, a hydrofluoric acid buffer would work best in a buffer range of around pH = 3.18.