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# Calculating the pH of a buffer

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1. Can you always use the Henderson Hasselbach equation or is it only when the concentration of the weak acid and its salt are equal? I'm self teaching so somewhat struggling with this section!

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2. (Original post by TomFitness)
Can you always use the Henderson Hasselbach equation or is it only when the concentration of the weak acid and its salt are equal? I'm self teaching so somewhat struggling with this section!

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Yes!
When the [acid] = [salt] then pH=pKa.
https://en.m.wikipedia.org/wiki/Hend...balch_equation
(I meant to say yes originally before editing).
3. (Original post by TomFitness)
Can you always use the Henderson Hasselbach equation or is it only when the concentration of the weak acid and its salt are equal? I'm self teaching so somewhat struggling with this section!
You can always use it.

When [A-]=[HA] it simplifies nicely. But so does just using Ka.
4. (Original post by Pigster)
You can always use it.

When [A-]=[HA] it simplifies nicely. But so does just using Ka.
Bit conflicting, why does the other guy say no?

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5. S/he might have been answering "No." to your second Q (is it only when the concentration of the weak acid and its salt are equal?).

I'm not a fan of H-H; I don't think it is any easier than just using Ka. But then again, I'm a bit of a mathophile. This is my tenth year of teaching A-level chemistry and I've got by without it.
6. (Original post by TomFitness)
Bit conflicting, why does the other guy say no?

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I meant to say yes. Sorry about that.
7. (Original post by B_9710)
I meant to say yes. Sorry about that.
Thanks!

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