Answer to Question #307998 in General Chemistry for Jaja

Question

How much 0.1 F HC2H3O2 is required to make 500ml of solution with a pH of 4.0?

Answer 1

HC₂H₃O₂ is the acetic acid - CH₃COOH;

[H+] = 10^-pH = 10^-4 = 0,0001М;

pK_a(CH₃COOH) = 4.75;

K_a(CH₃COOH) = 10^{-pKa(CH3COOH)} = 10^-4.75 = 1.8 * 10^-5;

CH₃COOH = H⁺ + CH₃COO^-

x 0 0

-0.0001 0.0001 0.0001

x-0.0001 0.0001 0.0001

K_a = [H⁺] * [CH₃COO^-]/[CH₃COOH];

Ka = 0.0001 * 0.0001/(x-0.0001);

1.8*10^-5 = 1*10^-8/(x-0.0001);

x-0.0001 = 1*10^-8/1.8*10^-5 = 5.56 * 10^-2;

x = 5.56 * 10^-2 + 0.0001 = 5.57 * 10^-2;

C₁ * V₁ = C₂ * V₂;

5.57 * 10^-2 * 500 = 0.1 * Y;

Y = 5.57 * 10^-2 * 500/0.1 = 278.5 mL.

Answer: 278.5 mL.