Ionization reaction

Question

If 0.1 mole of HCl is added to a 1 liter of solution of 0.1M CH3COO–, how many mole of H+ions will be there in the solution?

(ignore volume change after mixing)

Answer 1

The chemical reaction that will take place upon addition of HCl is...

HCl(aq) + CH₃COO^-(aq) ===> CH₃COOH(aq) + Cl^-(aq)

Since CH₃COOH is a weak acid, it essentially takes the H⁺ donated by HCl out of solution.

In 1 liter of solution, there will be 0.1 moles of CH₃COO^-, so 0.1 moles of HCl can react, leaving 0 moles of H⁺ remaining.

The question asks how many moles of H+ ions will there be? To answer this part, one should look at the ionization of the CH3COOH that is present.

CH₃COOH(aq) ==> H⁺ + CH₃COO^-

Ka = 1.8x10^-5 = [H⁺][CH3COO^-]/[CH3COOH]

1.8x10^-5 = (x)(x)/0.1 -x and assuming x is small relative to 0.1 M, we can ignore it.

1.8x10^-5 = x²/0.1

x² = 1.8x10^-6

x = [H⁺] = 1.34x10^-3 M = 1.34x10^-3 moles of H⁺ in the 1 liter of solution.