When a 100 mM aq solution of sodium acetate was prepared in the lab it had a pH of 8.9.
Calculate the amount of acetic acid (in g) to be added to 0.5 L of this sodium acetate
solution in order to bring its pH to the target value of 5.00.
Didn't I do this for you yesterday? I think so.
http://www.jiskha.com/display.cgi?id=1428706410
If there is something you don't understand follow up with that post instead of posting it all over again. If you didn't get the answer in your database, post your work and I'll find the error.
(I) pH=4.48
(II)3.78g of acetic acid
i think i was wrong
To calculate the amount of acetic acid needed to lower the pH of the sodium acetate solution to a target value, we need to use the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation relates the pH of a solution to the concentration of the acid and its conjugate base. In this case, acetic acid and sodium acetate are a conjugate acid-base pair.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([A-]/[HA])
where pH is the target pH, pKa is the acid dissociation constant for acetic acid, [A-] is the concentration of the acetate ion (from the sodium acetate), and [HA] is the concentration of acetic acid.
First, we need to calculate the concentration of acetate ion ([A-]) in the original solution. Since the sodium acetate is 100 mM, the concentration of acetate ion is also 100 mM.
Next, we need to find the acid dissociation constant (pKa) for acetic acid. The pKa value for acetic acid is 4.76.
Now, we can rearrange the Henderson-Hasselbalch equation to solve for the concentration of acetic acid ([HA]) needed:
[HA] = [A-] * 10^(pH - pKa)
Substituting the values into the equation:
[HA] = 100 mM * 10^(5.00 - 4.76)
[HA] = 100 mM * 10^0.24
[HA] = 100 mM * 1.585
[HA] = 158.5 mM
To convert this concentration to grams, we need to use the molecular weight of acetic acid, which is 60.05 g/mol.
Mass of acetic acid needed = [HA] * volume of solution
Mass of acetic acid needed = (158.5 mM * 0.5 L) * (60.05 g/mol / 1000 mM)
Mass of acetic acid needed = 12.52125 g
Therefore, approximately 12.52 grams of acetic acid should be added to 0.5 L of the sodium acetate solution to achieve a pH of 5.00.