Answer:
(1) pH of the Buffer solution = 4.82
(2) pH of Buffer solution after addition of HI = 4.6
Explanation:
(1) A buffer solution consisting a mixture of a weak acid and its conjugate base is termed as Acidic Buffer.
CH₃COOH is a weak acid and its conjugate base CH₃COO⁻ is strong.
Ka (acid dissociation constant) = 1.80 x 10⁻⁵
⇒pKa = -Log(1.80 x 10⁻⁵ )
⇒pKa = 4.82
Using Henderson equation
pH = pKa + Log[tex]\frac{[Salt]}{[Acid]}[/tex]
pH = 4.82 + Log[tex]\frac{0.353}{0.353}[/tex]
pH = 4.82
(2) HI is a strong acid and dissociate completely.
HI ⇆ H⁺ + I⁻
Due to its complete ionization a common ion effect arrises .
Assume all acid react with acetate ion to produce acetic acid (CH₃COOH)
CH₃COO⁻ + H₃O⁺ ⇄ CH₃COOH + H₂O
[H₃O⁺] added = 1 lit 0.09 mole = 0.09 molar
[CH₃COOH] = 0.353 + 0.09 = 0.443
[CH₃COO⁻] = 0.353 - 0.09 = 0.263
Using Henderson equation
pH = pKa + Log[tex]\frac{[Salt]}{[Acid]}[/tex]
pH = 4.82 + Log[tex]\frac{0.263}{0.443}[/tex]
pH = 4.82 - .22 = 4.6
