What is the relationship between pH and hydrogen ion concentration?

The relationship between pH and hydrogen ion concentration is characterized as an inverse relationship. This relationship arises from the definition of pH, which is the negative logarithm of the hydrogen ion concentration. Specifically, as the concentration of hydrogen ions in a solution increases, the pH value decreases, indicating a more acidic solution. Conversely, when the hydrogen ion concentration decreases, the pH value increases, indicating a more basic (alkaline) solution.

For example, a solution with a high concentration of hydrogen ions (e.g., 0.01 moles per liter) will have a low pH (around 2), whereas a solution with a low concentration of hydrogen ions (e.g., 0.0001 moles per liter) will have a higher pH (around 4). This logarithmic scale means that even small changes in hydrogen ion concentration result in significant changes in pH, reinforcing the concept of the inverse relationship between the two.