1. Initial:
- Before mixing the acid and base, the pH of the reaction mixture depends on the starting materials:
- If the solution contains a stronger acid, the pH will be lower (more acidic).
- If the solution contains a stronger base, the pH will be higher (more basic).
2. Mixing:
- When the acid and base are mixed, the reaction begins, and the hydrogen ions (H+) from the acid start to combine with the hydroxide ions (OH-) from the base to form water (H2O).
3. pH changes:
- As the reaction progresses, the concentration of H+ and OH- ions in the solution decreases. This decrease causes the pH value of the mixture to shift toward a neutral value (pH = 7).
- The pH will gradually rise if the initial solution was acidic (moving from low pH to 7) or fall if it was basic (moving from high pH to 7).
4. Endpoint:
- At a certain point, called the equivalence point, the reactants will be present in stoichiometrically equal amounts, and their complete neutralization will occur.
- At this point, the pH of the solution will be exactly 7, indicating a neutral solution.
5. Beyond Endpoint:
- If you add more acid after reaching the equivalence point, the H+ ions from the excess acid will cause the pH to drop below 7, making the solution acidic again.
- Similarly, adding more base after the equivalence point will increase the OH- concentration, raising the pH above 7 and making the solution basic.
