Final answer:
The pH of air-saturated distilled water with a hydronium ion concentration of 2.0 × 10⁻⁶ M can be calculated using the formula pH = -log[H₃O⁺], resulting in a slightly acidic pH value of approximately 5.70.
Step-by-step explanation:
Calculating the pH of Air-Saturated Distilled Water
When carbon dioxide (CO₂) dissolves in water, it forms carbonic acid (H₂CO₃), which can then release hydronium ions (H₃O⁺) into the solution. In the case of air-saturated distilled water, this results in a higher hydronium ion concentration compared to pure water. The hydronium ion concentration in question is given as 2.0 × 10⁻⁶ M. To find the pH, we use the formula:
pH = -log[H₃O⁺]
Substituting the given concentration:
pH = -log(2.0 × 10⁻⁶)
This calculation results in a pH value of approximately 5.70, indicating that the dissolved CO₂ creates a slightly acidic solution. It's important to note that this pH is lower than the pH of pure water due to the presence of carbon dioxide causing the formation of carbonic acid.