1. Calculate pH of an acetate buffer containing 27.5 mM acetic acid (pKa is 4.74) and 50 mM sodium acetate. When a 30 mM aq solution of sodium acetate was prepared in the lab it had a pH of 8.8. 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.
a. pH = 4.74 + log(base)/(acid) = approx 5.00
b.
millimoles NaAc = mL x M = 500 mL x 0.030M = = 15 mmoles.
5.00 = 4.74 + lot (15/x)
Solve for x = millimoles acetic acid and convert that to grams in 500 mL solution.
Thank you :)
To calculate the amount of acetic acid to be added to the sodium acetate solution in order to bring its pH to the target value of 5.00, we need to use the Henderson-Hasselbalch equation. This equation relates the pH of a buffer solution to the pKa and the concentrations of the acid and its conjugate base.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([conjugate base]/[acid])
In this case, the acid is acetic acid (CH3COOH) and its conjugate base is sodium acetate (CH3COONa). We are given that the pKa value of acetic acid is 4.74.
Step 1: Calculate the initial concentrations of acid and conjugate base in the solution.
Given:
- Concentration of sodium acetate (conjugate base) = 50 mM
- pH of the solution = 8.8
To calculate the concentration of the acid, we use the equation:
[acid] = [conjugate base] * 10^(pH - pKa)
Substituting the given values:
[acid] = 50 mM * 10^(8.8 - 4.74)
Step 2: Calculate the final concentration of acid needed to achieve the target pH.
Given:
- Target pH = 5.00
To calculate the final concentration of the acid, we rearrange the Henderson-Hasselbalch equation:
[acid] = [conjugate base] * 10^(pH - pKa)
Substituting the known values:
[acid] = 50 mM * 10^(5.00 - 4.74)
Step 3: Calculate the amount of acetic acid to be added.
Given:
- Volume of sodium acetate solution = 0.5 L
To calculate the amount of acetic acid needed, we use the equation:
Amount (g) = [acid] * volume (L) * molar mass (g/mol)
Substituting the known values:
Amount (g) = [acid] * 0.5 L * molar mass of acetic acid
Now, you can follow these steps and plug in the values to calculate the amount of acetic acid (in grams) to be added to the sodium acetate solution to bring its pH to the target value of 5.00.