Achieve #3 (weeks 2-3)

[205282258]

Can someone help me figure out what I'm doing wrong in this problem? I keep getting the pH as 2 and the pOH as 12. I did the ICE table and got Ka = (x^2)/(0.1158 - x) = 8.4E-4 and tried both including and excluding the -x because the Ka is so much smaller than the 0.1158M solution. For both ways I got the same pH and pOH.

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.

[Melinda Luo 2G]

Hmm, that's weird, your steps are correct, and I also calculated the answer myself and got the same values as you. You might want to double-check how you rounded your answers since Achieve usually wants at least two decimal places in the answer.

[Isabella Yee 1F]

Like Melinda suggested, you should check your rounding. Maybe try to avoid rounding until the final answer so that you can get a more accurate answer.

[Irene Kim 3E]

I agree with the previous responses - I had very similar values to yours but had to put in specific values to get correct answers (i.e., I didn't round anything in the calculator and rounded final answers to the hundredth place).

[Chloe Fuson]

i had this exact same problem and all of your steps are correct, the only issue was with rounding. When I left my pH as 2.03 and then subtracted that from 14, I then got 11.97, which ended up being the right answer. I guess achieve just isn't bothering with sig figs for this problem.