Air saturated water has a hydronium concentration of 2.0 x 10^-6 M from dissolved carbon dioxide. What is its pH?

1. Carbon dioxide dissolves and reacts with water to form carbonic acid, which supplies protons. 2. Take the logarithm of 2.0 x 10^-6 as log 2.0 plus log 10^-6. 3. Those parts are 0.30 and minus 6, giving minus 5.70. 4. Reversing the sign gives pH = 5.70. 5. Quoting 6.30 comes from subtracting 0.30 from 6 rather than adding it. 6. This concentration is about twenty times that of pure water, so the pH is well below 7. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.2 pH and pOH_