Question

A buffer solution is prepared by mixing 250. ml of 1.00 M CH3COOH with 500. ml of 0.500 M calcium acetate, Ca(CH3COO)2. Calculate the pH. Ka for CH3COOH is 1.8 – 10–5.

A) 2.96
B) 4.18
C) 5.40
D) 6.72

Answer 1

To calculate the pH of the buffer solution, the Henderson-Hasselbalch equation is used. The molarities of acetic acid and acetate ion are computed after mixing and then applied to find the pH, which is approximately 5.22.

Step-by-step explanation:

To calculate the pH of the given buffer solution, we need to use the Henderson-Hasselbalch equation, which relates the pH of a buffer to its acid and conjugate base concentrations and the acid's dissociation constant (Ka).

The reaction of acetic acid (CH3COOH) with calcium acetate (Ca(CH3COO)2) in the buffer solution forms acetate ions and hydrogen ions. Since calcium acetate is a salt of a weak acid and a strong base, it will completely dissociate in the solution and will not affect the pH by the hydrolysis of the ions.

First, we need to calculate the molarities of acetic acid and acetate ion after mixing:

• Acetic acid molarity after dilution: M1V1 = M2V2; 1.00 M * 0.25 L = M2 * 0.75 L; M2 = (1.00 * 0.25)/0.75 = 0.333 M
• Calcium acetate provides two acetate ions per molecule, so its concentration will be twice the molarity of the calcium acetate: 0.5 M * 2 = 1 M acetate ion

Using the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])
pH = -log(1.8 * 10-5) + log(1/0.333)
pH = 4.74 + log(3.00)
pH = 4.74 + 0.477
pH = 5.217

Thus, the pH of the buffer solution is approximately 5.22, which is not given in the answer options. There might be a mistake or typo in the provided options.