Question

Calculate the pH of a buffer solution prepared by mixing 60.0 mL of 1.00 M lactic acid and 25.0 mL of 1.00 M sodium lactate.

(The pKa for lactic acid is 3.86. The molar mass for lactic acid is 90.1 g/mol and the molar mass for sodium lactate is 112.1 g/mol.)

Answer 1

To calculate the pH of a buffer solution, use the Henderson-Hasselbalch equation and the given concentrations of lactic acid and sodium lactate. Apply the equation pH = pKa + log([conjugate base]/[acid]).

Step-by-step explanation:

pH Calculation of a Buffer Solution:

To calculate the pH of a buffer solution, we need to use the Henderson-Hasselbalch equation. First, we need to determine the concentrations of lactic acid and sodium lactate in the final solution. We can use the equation C1V1 = C2V2 to find the moles of lactic acid and sodium lactate in the mixture. Then, we can apply the Henderson-Hasselbalch equation to find the pH of the buffer solution. The equation is pH = pKa + log([conjugate base]/[acid]). In this case, the acid is lactic acid and the conjugate base is lactate. Use the given pKa value of 3.86 to find the pH of the buffer solution.

Answer 2

This problem could be solved easily using the Henderson-Hasselbach equation used for preparing buffer solutions. The equation is written below:

pH = pKa + log[(salt/acid]

Where salt represents the molarity of salt (sodium lactate), while acid is the molarity of acid (lactic acid).

Moles of salt = 1 mol/L * 25 mL * 1 L/1000 mL = 0.025 moles salt
Moles of acid = 1 mol/L* 60 mL * 1 L/1000 mL = 0.06 moles acid
Total Volume = (25 mL + 60 mL)*(1 L/1000 mL) = 0.085 L

Molarity of salt = 0.025 mol/0.085 L = 0.29412 M
Molarity of acid = 0.06 mol/0.085 L = 0.70588 M

Thus,
pH = 3.86 + log(0.29412/0.70588)
pH = 3.48