What is the concentration of the acetate ion of an aqueous solution measured to be 0.20 M acetic acid in 0.20 M hydrochloric acid? (K_a for acetic acid = 1.8 × 10^-5) A)3.6 × 10^-5M B)9.0 × 10^-6M C)1.8 × 10^-5M D)7.2 × 10^-5M E)0.20 M

Question

Quizplus · Accepted Answer

For the reaction, 
CH3COOH + H2O ⇌ CH3COO- + H3O+ 
Ka = 1.8 × 10-5 
At equilibrium, 
Ka = [CH3COO-] [H3O+] / [CH3COOH] 
[CH3COO-] = Ka * [CH3COOH] / [H3O+] 
Given, [CH3COOH] = 0.20 M, [HCl] = 0.20 M 
[H3O+] = [Cl-] = 0.20 M (assume complete ionization of HCl) 
[CH3COO-] = (1.8 × 10-5) * (0.20) / (0.20) = 1.8 × 10-5 M 
Therefore, the concentration of the acetate ion is 1.8 × 10-5 M, which is closest to option C).

What Is the Concentration of the Acetate Ion of an Aqueous