What is the pH of 10⁻⁸ M HCl?

The pH of a solution is a measure of its acidity or basicity. For a strong acid like hydrochloric acid (HCl), we can calculate the pH based on its concentration.

Understanding Concentration

In this case, we have a concentration of 10⁻⁸ M HCl. However, since HCl is a strong acid, it fully dissociates in water. This means that the concentration of hydrogen ions (H⁺) contributed by HCl is equal to its concentration, which is 10⁻⁸ M.

Considering Water's Contribution

Pure water also contributes H⁺ ions, which adds complexity. The concentration of H⁺ ions in pure water at 25°C is 10⁻⁷ M. Therefore, we need to account for both sources of H⁺ ions:

• From HCl: 10⁻⁸ M
• From water: 10⁻⁷ M

Calculating Total H⁺ Concentration

The total concentration of H⁺ ions in the solution is:

[H⁺] = 10⁻⁸ M + 10⁻⁷ M = 1.1 × 10⁻⁷ M

Finding the pH

The pH is calculated using the formula:

pH = -log[H⁺]

Substituting the total concentration:

pH = -log(1.1 × 10⁻⁷)

This results in a pH of approximately 6.96.

Final Result

Thus, the pH of a 10⁻⁸ M HCl solution is about 6.96, indicating that it is slightly acidic due to the contribution from both the acid and the water.