I have just been studying the $\ce{HCl}$-$\ce{KCl}$ 'buffer', but there are still quite a few things I am uncertain about. I would appreciate any help in clearing up some questions I have.
What I understand (possibly incorrectly) from my research so far:
Water is the weak acid acting as a buffer in this system. The $\ce{HCl}$ and $\ce{KCl}$ in the system are there to increase the solution's ionic strength, which somehow improves water's buffer capacity. In high ionic strength solutions, the 'standard' equilibrium equation has to be changed to include the activity coefficients. For water's equilibrium, as the ionic strength increases, the activity constants decrease and so the K value decreases.
If anything above is incorrect, please point out my misunderstanding. There are still a few questions I can't find answers to:
- Why does the increased ionic strength of the solution improve water's buffer capacity?
- Isn't a higher equilibrium constant required to make water a better buffer? Then isn't it bad that the ionic strength decreases K?
- Could any other salt have been used to increase the ionic strength, or is there some specific reason $\ce{HCl}$-$\ce{KCl}$ is used?
I'm finding this 'buffer' system to be extremely confusing, so any help answering these questions would be greatly appreciated.
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