A buffer contains a weak acid, HA, and its conjugate
base. The we...

Question

A buffer contains a weak acid, HA, and its conjugate
base. The weak acid has a pKa of 4.5, and the buffer has a
pH of 4.3. Without doing a calculation, state which of
these possibilities are correct at pH 4.3. (a) 3HA4 = 3A-4,
(b) 3HA4 7 3A-4, or (c) 3HA4 6 3A-4. [Section 17.2]

Accepted Answer

Hello everyone. So in this video we are concerning a buffer solution that's prepared using HF and f minus were given the P. K. As well as ph And we're trying to see which of the following is applicable at P. H with 3.35 value. And we're going to perform no calculations whatsoever. So we don't do any calculations. But we still want to go ahead and think about the Great Henderson Hasselbach equation. And to refresh your memories, let's go ahead and write this out. So the Henderson Hasselbach equation is where ph is equal to the P. K. A. Plus the log of well our concentration of our conjugate base which I just put a CB over the concentration concentration, I'm sorry of weak acid, which I'll just simplify to W. A. So in the case that we have, well we have three situations we have if that the ph will be less than the P. K. And that's if and only if so maybe I would say maybe a different color. I'll put that part as the concentration of our weak acid is going to be greater than the concentration of our conjugate base. Second scenario is if our P H. Is greater than R P K. A. And that's responsible if the concentration of our weak acid is less than our concentration of our conjugate base. Last scenario is if R P H. Is equal to the P A. K. A. And that's responsible if the concentration number W. A. R, weak acid is equal to the concentration of the conjugate base. So here are weak acid. So weak acid is equal to R h F and R contribute base is f minus. Were given that the p k A is 3.16 and the p h is 3.35. We see here that the ph is going to be greater than r p k A. And because we have that situation, we see that this this right here. And of course just plugging in those simplifications of HF and F minus. We see here that our final answer is going to be C. And she's going to be my final answer for this question. Thank you all so much for watching.

Watch next