Answer to Question #350339 in Chemistry for ami

Question

1.     Determine the pH of a buffer prepared by adding 15 mL of 0.25 M acetic acid to 35 mL of 0.17 M sodium acetate. Given Ka for acetic acid = 1.7 x 10^-5.

Answer 1

Solution:

acetic acid = CH₃COOH

sodium acetate = CH₃COONa

Total volume of solution = Volume of CH₃COOH + Volume of CH₃COONa

Total volume of solutio = 15 mL + 35 mL = 50 mL

Calculate new concentrations considering dilution:

[CH₃COOH] = (0.25 M) × (15 mL / 50 mL) = 0.075 M

[CH₃COONa] = (0.17 M) × (35 mL / 50 mL) = 0.119 M

The Henderson-Hasselbalch equation is commonly used to calculate the pH of a buffer solution from the concentration of the buffer components:

where pK_a is the acid dissociation constant and [base] and [acid] are the base and acid concentrations, respectively.

In this case, the base is CH₃COONa_, and the acid is CH₃COOH.

Therefore,

pH = −log(1.7 × 10⁻⁵) + log(0.119 M / 0.075 M) = 4.97

pH = 4.97

Answer: pH = 4.97