A strong acid completely dissociates in water, releasing all of its hydrogen ions (H+). A weak acid, on the other hand, only partially dissociates, releasing only a small fraction of its hydrogen ions.

When equal volumes of a strong acid and a weak acid of equal concentration are mixed, the resulting solution will contain more hydrogen ions from the strong acid than from the weak acid. This is because the strong acid completely dissociates, while the weak acid only partially dissociates.

The higher concentration of hydrogen ions in the solution will cause the pH to be lower than 7. A pH of 7 is considered neutral, so a pH below 7 indicates an acidic solution.