Question

A sample of pure water is neutral because it contains

Answer 1

• A sample of pure water is neutral because it contains the same number of H₃O⁺ ions as OH⁻ ions

Step-by-step explanation:

• Neutral pH is 7.

• By definition pH = - log [H₃O⁺]

• Water ionizes according to this equilibrium equation:

2 H₂O (l) ⇄ H₃O⁺ + OH⁺

• So, the ionization (equlibrium) constant is:

Kw = [H₃O⁺ ] [ OH⁺]

• At 25°C, Kw = 1 × 10⁻¹⁴

• Hence: [H₃O⁺ ] [ OH⁺] = [H₃O⁺ ] ² = 1 × 10⁻¹⁴ ⇒ [H₃O⁺ ] = 10⁻⁷

• ⇒ pH = - log (10⁻⁷) = 7