Answer to Question #157873 in Organic Chemistry for BessFren

Question

Calculate the H3O+ concentration and then pH in a 0.100 M HC2H3O2 solution that is 1.34% ionised?

Answer 1

HC₂H₃O₂ ≡ CH₃COOH - acetic acid

Solution:

HC₂H₃O₂(aq) + H₂O(l) ⇌ H₃O⁺(aq) + C₂H₃O₂^- (aq)

ICE Table:

[H₃O⁺] = [C₂H₃O₂^-] = αC (according to the ICE Table).

α = 1.34% = 0.0134

C = 0.100 M

Hence,

[H₃O⁺] = αC = 0.0134 × 0.100 M = 1.34×10^-3 M

[H₃O⁺] = 1.34×10^-3 M

pH is defined as the negative logarithm of [H₃O⁺]:

pH = -log[H₃O⁺]

pH = -log(1.34×10^-3) = 2.87

pH = 2.87

Answer: [H₃O⁺] = 1.34×10^-3 M; pH = 2.87