Ionic Equilibrium

• HCl is a monoprotic acid, so 0.1 M HCl provides 0.1 M H⁺ ions.
• H₂SO₄ is a diprotic acid, so 0.2 M H₂SO₄ provides 2 × 0.2 = 0.4 M H⁺ ions.

When equal volumes of the two solutions are mixed, the total volume doubles, and the concentration of each acid is halved:

New concentration of HCl =

New concentration of H₂SO₄ =

The total H⁺ concentration is:

The concentration of HCl is M. Since HCl is a strong acid, the [H⁺] from HCl is M. However, the autoionization of water also contributes [H⁺] = M. Therefore, the total [H⁺] is:

The pH is given by:

Thus, the pH is greater than 6 and less than 7.

Concept: Strong acid ⇒ full ionization. Use . Step 1: {\color{red}Concentrations.} Step 2: {\color{red}Equal volume mixing.} Average concentration: Step 3: {\color{red}Find pH.} So between 4 and 5.