Calculate the pH of a buffer prepared by mixing 0.10 mol of sodium formate and 0.05 mol of formic acid in 1.0 L of solution. (HCO2H: Ka = 1.8 x 10-4)
(a) 1.8 x 10-4
(b) 3.44
(c) 4.05
(d) 5.31
(e) none of the above
Chemistry · Sun Jul 10 2022
Answered on
To calculate the pH of a buffer, you need to use the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation is given by:
pH = pKa + log ([A-]/[HA])
Where pH is the measure of how acidic or basic a solution is, pKa is the negative logarithm of the acid dissociation constant (Ka) of the weak acid in the buffer, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.
In this case, the weak acid is formic acid (HCO2H), and its conjugate base is sodium formate (HCO2Na).
Step 1: Calculate the concentrations of the weak acid and the conjugate base. Given: 0.10 mol of sodium formate and 0.05 mol of formic acid
The total volume of the solution is 1.0 L, so the concentration of sodium formate ([A-]) is 0.10 mol/L. The concentration of formic acid ([HA]) is 0.05 mol/L.
Step 2: Calculate the pKa value. Given: Ka = 1.8 x 10^-4
To calculate pKa, take the negative logarithm of Ka: pKa = -log (1.8 x 10^-4) = 3.74
Step 3: Plug the values into the Henderson-Hasselbalch equation. pH = pKa + log ([A-]/[HA]) pH = 3.74 + log (0.10/0.05) pH = 3.74 + log 2 pH = 3.74 + 0.301 pH ≈ 4.04
Therefore, the pH of the buffer prepared by mixing 0.10 mol of sodium formate and 0.05 mol of formic acid in 1.0 L of solution is approximately 4.04.
A buffer solution is a solution that can resist changes in pH when a small amount of acid or base is added to it. It consists of a weak acid and its conjugate base. The weak acid provides the H+ ions, and the conjugate base reacts with any additional H+ ions added to maintain a relatively constant pH. The Henderson-Hasselbalch equation is used to calculate the pH of a buffer by taking into account the concentrations of the weak acid and its conjugate base. By maintaining a constant pH, buffer solutions are used in various biological, chemical, and pharmaceutical applications.