Explain what happens to the pH of a buffered solution when hydrogen ions are added. Why does this happen?

Verified step by step guidance

1. Understand the concept of a buffer: A buffer is a solution that resists changes in pH when small amounts of an acid (H⁺ ions) or a base (OH⁻ ions) are added. It typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid.
2. Recognize the role of hydrogen ions (H⁺): When hydrogen ions are added to a buffered solution, they interact with the conjugate base present in the buffer system. The conjugate base reacts with the H⁺ ions to form the weak acid, thereby reducing the free H⁺ concentration in the solution.
3. Write the chemical reaction: For example, in an acetic acid buffer system (CH₃COOH/CH₃COO⁻), the reaction would be: ${\mathrm{CH}3\mathrm{COO}}_{-}+H_{+}\to {\mathrm{CH}3\mathrm{COOH}}_{}$
4. Explain why the pH change is minimal: The buffer system minimizes the change in pH because the added H⁺ ions are 'absorbed' by the conjugate base, forming the weak acid. This prevents a significant increase in the concentration of free H⁺ ions, which would otherwise lower the pH drastically.
5. Conclude with the buffering capacity: The ability of the buffer to resist pH changes depends on the concentration of the weak acid and its conjugate base. If too many H⁺ ions are added, the buffer may become overwhelmed, and the pH will change more significantly.

Key Concepts

Buffered Solution

A buffered solution is a system that resists changes in pH when small amounts of an acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. This equilibrium allows the buffer to neutralize added hydrogen ions (H+) or hydroxide ions (OH-), maintaining a relatively stable pH.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, while values below 7 indicate acidity and above 7 indicate alkalinity. The pH is logarithmically related to the concentration of hydrogen ions in the solution, meaning that even small changes in H+ concentration can significantly affect pH.

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. In the context of a buffered solution, when hydrogen ions are added, the buffer components react to minimize the change in pH, thus maintaining the solution's stability.