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Stuck on this problem

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Borek:

--- Quote from: tkle28 on May 11, 2023, 07:05:03 AM ---Is it whenever it’s weak?
--- End quote ---

No. Just because it is weak is not enough.

In general this formula works reasonably well when the acid is dissociated less than 5%. Is this the case?

Aldebaran:
Well solving the quadratic is pretty tedious but I persevered and get 2.199. However it’s rather late at night here and I may well have made a slip or rounding error. I might check it in the morning when I’m more awake.

Borek:
2.20 is what I got as well.

(lol, you haven't seen really tedious calculations yet :D )

Aldebaran:
To help the OP. Looking at your calculations there’s an error other than the approximation. Root of 0.00068 x 0.065 is 6.6483 x 10^-3 and the log of this is - 2.177 giving pH 2.18 as per the given answer. So it seems the question assumes the approximation method was expected.

Borek:

--- Quote from: Aldebaran on May 12, 2023, 07:02:04 AM ---So it seems the question assumes the approximation method was expected.

--- End quote ---

At nearly 10% dissociation that's a bad idea (I don't blame you for checking, I blame whoever asked the question and expected the answer).

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