Answer to Question #90385 in Physical Chemistry for mayur

Question

A solution contains 0.05 M acetic acid and 01 M sodium acetate. Calculate the concentration of H+,
when HC1 is added to the solution such that
[HC1] = 1.0 x 10-3M.
Kafor acetic acid = 1.8 x 10-5.

Answer 1

Solution.

A solution consisting of a solution of acetic acid and sodium acetate is considered as a buffer system of a weak acid and a salt of a weak acid. Therefore, we use the following formula:

$$pH = pKa - lg{\frac{C(acid)}{C(salt)}}$$

pH = 5.041

If we add acid or base to the buffer, then the equilibrium will shift and the formula will take the following form:

$$pH = pKa - lg{\frac{C(acid)+X}{C(salt)-X}}$$

H⁺ + CH3COO^- = CH3COOH

$$pH = 4.74-lg{\frac{0.05+10^{-3}}{0.1-10^{-3}}}$$

pH = 5.028

$$[H+] = 9.736 \times 10^{-6}$$

Answer:

$$pH = 5.028$$

or

$$[H+] = 9.736 \times 10^{-6}$$