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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](https://tex.z-dn.net/?f=pH%3DpKa%2Blog%28%20%5Cfrac%7B%5BA%5E%7B-%7D%5D%20%7D%7B%5BHA%5D%7D%20%29%20%5C%5C%20%5C%5C%20if%20%5BA%5E%7B-%7D%5D%3D%5BHA%5D%20%5C%5C%20%5C%5C%20pH%3DpKa%20%2B%20log%20%281%29%20%5C%5C%20%5C%5C%20pH%3DpKa%20%2B%200%3D5%2C25)
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!
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:
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!