If a base is added to pure water, why does the [H₃O⁺] decrease?

Verified step by step guidance

1. insert step 1> When a base is added to pure water, it increases the concentration of hydroxide ions (OH⁻) in the solution.
2. insert step 2> According to the water dissociation equilibrium, H₂O ⇌ H⁺ + OH⁻, the addition of OH⁻ shifts the equilibrium to the left, reducing the concentration of hydronium ions (H₃O⁺).
3. insert step 3> This shift is explained by Le Chatelier's principle, which states that a system at equilibrium will adjust to counteract any changes imposed on it.
4. insert step 4> As the concentration of OH⁻ increases, the equilibrium shifts to reduce the concentration of H⁺ (or H₃O⁺), thus decreasing [H₃O⁺].
5. insert step 5> The decrease in [H₃O⁺] results in an increase in pH, making the solution more basic.

Key Concepts

Acid-Base Chemistry

Acid-base chemistry involves the study of substances that can donate protons (H⁺ ions) or accept them. In this context, bases are substances that can accept protons, leading to a decrease in the concentration of hydronium ions (H₃O⁺) in solution. Understanding the behavior of acids and bases is crucial for grasping how they interact with water.

Hydronium Ion Concentration

The concentration of hydronium ions ([H₃O⁺]) in a solution is a measure of its acidity. When a base is added to pure water, it reacts with the H⁺ ions, forming water and reducing the number of H₃O⁺ ions present. This shift in ion concentration is fundamental to understanding changes in pH and the overall acidity of the solution.

pH Scale

The pH scale quantifies the acidity or basicity of a solution, ranging from 0 to 14. A pH less than 7 indicates acidity, while a pH greater than 7 indicates basicity. When a base is added to water, the decrease in [H₃O⁺] results in an increase in pH, illustrating the inverse relationship between hydronium ion concentration and pH.