Respuesta :

Edufirst

Answer:

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

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

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