Calculate the pH for an aqueous solution of acetic acid that contains 5.15 × 10^-3 mol L^-1hydronium Ion. A)1.94 × 10^-12 B)5.15 × 10^-3 C)2.288 D)11.712

Question

Quizplus · Accepted Answer

Acetic acid is a weak acid and its dissociation can be represented as follows: 
CH3COOH + H2O ⇌ CH3COO- + H3O+

The equilibrium constant expression for this reaction is: 
Ka = [CH3COO-][H3O+]/[CH3COOH]

Given that the concentration of H3O+ is 5.15 × 10-3 M, and assuming that the initial concentration of acetic acid is equal to the final concentration, we can write:

Ka = (5.15 × 10-3)2 / (5.15 × 10-3) = 5.15 × 10-3
(Note: we neglect the contribution of x to [CH3COOH] since x is much smaller than 5.15 × 10-3 M)

The pH of the solution can be calculated from the equilibrium expression for H3O+: 
pH = -log[H3O+] = -log(5.15 × 10-3) = 2.288

Therefore, the correct answer is C.

Calculate the PH for an Aqueous Solution of Acetic Acid