Achieve #3 Week 2

[Desiree Eshraghi 3A]

Muscles produce lactic acid, CH3CH(OH)COOH(aq) , during exercise. Calculate the percent ionization (deprotonation), pH, and pOH of a 0.1039 M solution of lactic acid. The acid‑dissociation (or ionization) constant, Ka , of this acid is 8.40×10−4 .

Although I was able to get the percent ionization, I keep getting stumped at finding pH and pOH - I have no idea what I am getting wrong. For reference, I am getting approximately 1-2 and 12-13 respectively after multiple calculation attempts. Any help would be appreciated. Thanks!

[Mari Masunaga 1G]

Hi! I'm sorry this is happening to you :(
The most I can suggest is using your numerator exactly from the percent ionization to find the pH. Something like -log(numerator). hope this helps!

[Jacqueline Vargas 3L]

Hi!

Another tip. Try putting your answer with two decimal places, so if for pH = -log (H3O+) you are getting 1.3456789, input 1.35. That's what worked for me.

[Kitana_Garcia_3A]

Yea, Lavelle mentioned in his lecture that when there are 2 sig figs, to use 2 decimal places. Hope this helps :)

[405566265]

to find the pH and pOH, you first need to calculate x (the concentration of the ionized) which you must have done correctly if you got the correct percent ionized. simply take the -log10 of that number to get the pH. Subtract the pH from 14.00 to get the pOH.

[benkw_3I]

You may want to find the concentration of H+ using the full Ka formula where you solve using the quadratic formula. If you simplified your equation by ignoring the dissociation of lactic acid you may still have been able to get the first answer right but not the others due to error tolerance.

[Savannah Licciardello 2C]

Try simplifying the H30 concentration when calculating the pH and pOH. If that does not work then I suggest not simplifying when calculating x, even though you can due to the Ka value. That may make it more accurate.