calculate the concentration of acetic acid in a 0.85 M sodium acetate solution,when pH=7,knowing that for the acetic acid,Ka= 1.76 x 10-6
To calculate the concentration of acetic acid in a sodium acetate solution knowing the pH and the acid dissociation constant (Ka), we need to use the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([A-]/[HA])
Where:
pH is the given pH value
pKa is the negative logarithm of the acid dissociation constant (Ka)
[A-] is the concentration of the conjugate base (acetate ion)
[HA] is the concentration of the weak acid (acetic acid)
Now, let's solve the equation to find the concentration of acetic acid.
Step 1: Determine the pKa value
pKa = -log(Ka)
= -log(1.76 x 10^-6)
≈ 5.754
Step 2: Substitute the given values into the Henderson-Hasselbalch equation
pH = 5.754 + log([A-]/[HA])
Step 3: Rearrange the equation to solve for [HA]
pH - 5.754 = log([A-]/[HA])
10^(pH - 5.754) = [A-]/[HA]
Step 4: Substitute the molar concentration of sodium acetate into the equation
10^(pH - 5.754) = [A-]/0.85
Step 5: Calculate the concentration of acetic acid ([HA])
[HA] = [A-] / 10^(pH - 5.754)
[HA] = 0.85 / 10^(7 - 5.754)
Step 6: Calculate the concentration of acetic acid using a calculator
[HA] ≈ 0.85 / 17.179
The concentration of acetic acid in the 0.85 M sodium acetate solution, given that the pH is 7 and Ka is 1.76 x 10^(-6), is approximately 0.0495 M.