- #1
Kavorka
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Homework Statement
When a weak acid HA is titrated 75% of its endpoint, it has a pH of 5.25. Calculate its Ka.
Homework Equations
Ka = [H+ ][A- ]/[HA]
[H+] = 10^-pH
The Attempt at a Solution
I found [H+ ] from the pH to be 10^-5.25 M. From the dissociation equation of HA, we know there is a one-to-one molar ratio between [H+ ] and [A- ], so [A- ] = 10^-5.25. We know that 75% of the original HA has been titrated with the reaction: HA(aq) + OH-(aq) <------> A-(aq) + H2O (l), so there is 3 times the amount of A- than HA (75%:25%).
Ka = [10^-5.25][10^-5.25] / [10-^5.25 / 3] Ka = 1.69x10^-5
Im just not sure if I'm doing this right