Question

How would one determine what weak acid/conjugate base pair would go into the creation of a buffer? Suppose you need to keep the pH of a solution near pH 2.5. Find a combination that you would use.

Answer 1

to prepare required pH buffer we need to select the pKa value acid which is very close to the pH value

here required pH value 2.5 . so we need acid and conjugate base which has pKa near to this value

H3PO4 , pKa value = 2.16

so we can use this for make 2.5 pH buffer

combinations needed = H₃PO₄ and H₂PO₄^-

pH = pKa + log [conjugate base / weak acid]

2.5 = 2.16 + log [conjugate base / weak acid]

log [conjugate base / weak acid] = 0.339

conjugate base / weak acid = 2.18

weak acid / conjugate base = 0.458