Achieve #3 % ionization (weeks 2-3)

[205282258]

Muscles produce lactic acid, CH3CH(OH)COOH(aq), during exercise. Calculate the percent ionization (deprotonation), pH, and pOH of a 0.1158M solution of lactic acid. The acid‑dissociation (or ionization) constant, Ka, of this acid is 8.40×10−4.

I got the x value for this problem as 0.01027. To find the % ionization I did 0.01027/0.1158 x 100% = 8.86, but achieve marks it as wrong. How do I do this part of the problem?

[Julie Tran 3C]

Hello,

If you did the approximation where you assumed that (0.1158-x) = 0.1158 in calculating that x = 0.01027, then that would have given you an incorrect answer because in this case the x value is greater than 5% of the original value. When I calculated it without that assumption, I got x = 0.009452.

Hope this helps!

[Madison Chan 3B]

Your work for % ionization is correct, but your x-value isn't exact enough which may be throwing the calculations off.
Try graphing 8.4 * 10^-4 and x^2 / 0.1005 - x in your calculator and use that to find the x-value where they intersect. I found this method to be a lot more accurate than making approximations, but not as tedious as trying to use the quadratic formula :))

[205282258]

Thank you so much!