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Anthony
28.01.13, 02:59
The % dissociated (or value "a") tells you that you have 3% of A- and
97% of HA. For a 0.25M solution, that means you have (0.97 * 0.25)M HA
present, (0.03 * 0.25)M A- present, and (0.03 * 0.25)M H+ present.
Putting these concentrations into the equation doesn't give you K =
0.0036. In fact, the first problem is that whoever answered before
assumes "% dissociated" is the concentration of H+ present...a mistake
which can be seen in solving the second part.
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Comments
The % dissociated (or value "a") tells you that you have 3% of A- and 97% of HA. For a 0.25M solution, that means you have (0.97 * 0.25)M HA present, (0.03 * 0.25)M A- present, and (0.03 * 0.25)M H+ present. Putting these concentrations into the equation doesn't give you K = 0.0036. In fact, the first problem is that whoever answered before assumes "% dissociated" is the concentration of H+ present...a mistake which can be seen in solving the second part.
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