When acids are dissolved in water, they produce an excess of hydrogen ions (H+) . This is why acids have a pH less than 7.

Here's why:

* Acids are proton donors: Acids donate hydrogen ions (protons) to the water molecules.

* Hydronium ions: The hydrogen ions (H+) combine with water molecules to form hydronium ions (H3O+).

* Increased acidity: The presence of excess hydronium ions in the solution increases the acidity, leading to a lower pH value.

Example:

Consider hydrochloric acid (HCl) dissolving in water:

HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)

In this reaction, HCl donates a proton (H+) to water, forming hydronium ions (H3O+) and chloride ions (Cl-). The excess of H3O+ ions makes the solution acidic.