Understanding the Concepts
* HCl is a strong acid: This means it completely ionizes in water, meaning every HCl molecule breaks apart into a hydrogen ion (H⁺) and a chloride ion (Cl⁻).
* pH: A measure of the acidity or alkalinity of a solution. It is calculated using the formula: pH = -log[H⁺]
* A low pH indicates a high concentration of H⁺ ions (acidic)
* A high pH indicates a low concentration of H⁺ ions (alkaline/basic)
Calculation
1. Determine the [H⁺]: Since HCl is a strong acid, the concentration of H⁺ ions is equal to the initial concentration of HCl: [H⁺] = 1 x 10⁻⁷ M.
2. Calculate the pH:
pH = -log[H⁺]
pH = -log(1 x 10⁻⁷)
pH = 7
Important Note: This calculation produces a pH of 7, which is neutral. However, pure water also has a pH of 7. In reality, the pH of a 1 x 10⁻⁷ M solution of HCl would be slightly less than 7 due to the very small contribution of H⁺ ions from the autoionization of water.
Therefore, the pH of a 0.0000001 M solution of hydrogen chloride in water is essentially neutral, but slightly acidic.
