Question

A buffer contains equal amounts of a weak acid and its conjugate base and has a ph of 5.25. part a which would be a reasonable value of buffer ph after the addition of a small amount of acid? which would be a reasonable value of buffer ph after the addition of a small amount of acid? 6.35 5.15 4.15 5.35

Answer 1

Hello!

After the addition of a small amount of acid, a reasonable value of buffer pH would be 5,15.

If initially there are equal amounts of a weak acid and its conjugate base, the pH would be equal to the pKa, according to the Henderson-Hasselbach equation:

$pH=pKa+log( \frac{[A^{-}] }{[HA]} ) \\ \\ if [A^{-}]=[HA] \\ \\ pH=pKa + log (1) \\ \\ pH=pKa + 0=5,25$

So, when adding a little amount of acid the pH should be only a little lower than the pKa. The value from the list that is a little lower than the pKa is 5.15

Have a nice day!