If you had an acetic acid solution that was 0.10 M, what would the acetate concentration have to be in order to get a pH of 5.35?
I tried doing [H+] = 10^(-pH), but I don't think that's right. Please help, I'm stuck.
if H+ is 10^-5.35, so the acetate concentration the same.
H acetate>><< H+ + aqcetate-
So the concentration would be [H+] = 4.47?
To find the concentration of acetate (C2H3O2-) needed to achieve a specific pH, you can use the Henderson-Hasselbalch equation. This equation relates the pH of a solution to the concentration of the acid and its conjugate base. The Henderson-Hasselbalch equation is as follows:
pH = pKa + log([A-] / [HA])
Where:
pH = the desired pH (in this case, 5.35)
pKa = the dissociation constant of the acid (acetic acid in this case)
[A-] = concentration of the acetate ion (C2H3O2-)
[HA] = concentration of the acid (acetic acid, CH3COOH)
First, you need to know the pKa value of acetic acid, which is 4.75.
Now, let's rearrange the Henderson-Hasselbalch equation to solve for [A-]:
pH - pKa = log([A-] / [HA])
Since acetic acid is a weak monoprotic acid, it can be assumed that it fully dissociates into acetate ions and hydrogen ions:
CH3COOH ⇌ CH3COO- + H+
Therefore, the concentration of acetic acid ([HA]) is equal to the concentration of hydrogen ions ([H+]) initially. So, let's rewrite the equation:
pH - pKa = log([A-] / [H+])
Rearranging the equation:
[A-] = [H+] × 10^(pH - pKa)
Now, you can substitute the given pH value (5.35) and the pKa value of acetic acid (4.75) into the equation:
[A-] = [H+] × 10^(5.35 - 4.75)
Next, you need to calculate the concentration of hydrogen ions ([H+]). You correctly stated that [H+] = 10^(-pH). Therefore:
[H+] = 10^(-5.35)
Finally, substitute the calculated value of [H+] into the equation to find [A-]:
[A-] = 10^(-5.35) × 10^(5.35 - 4.75)
Simplifying:
[A-] = 10^(-5.35 + 5.35 - 4.75)
[A-] = 10^(0.25)
Therefore, the concentration of acetate ([A-]) required to achieve a pH of 5.35 in a 0.10 M acetic acid solution is 10^0.25 or approximately 1.78 M.