ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

An increase in the concentration of hydroxide ions (OH-) indicates that the solution is becoming more basic. In the context of acid-base chemistry, the pH scale measures the acidity or basicity of a solution. When the concentration of OH- ions rises, it leads to a decrease in the concentration of hydrogen ions (H+) due to the ion product of water (Kw).

In a basic solution, there is a higher concentration of OH- compared to H+. For example, when a strong base such as sodium hydroxide (NaOH) is dissolved in water, it dissociates to produce more OH- ions, consequently increasing the solution's basicity and raising its pH above 7.

On the other hand, an acidic solution would have a higher concentration of H+ ions and a lower concentration of OH- ions, leading to a pH below 7. A neutral solution has equal concentrations of H+ and OH- ions, typically found in pure water. An electrolyte solution simply refers to a solution that conducts electricity due to the presence of free ions, and while increases in OH- can occur in such solutions, it does not specifically indicate the nature of the solution in terms of its acidity or basicity.

Thus