slimt1545 slimt1545
  • 26-03-2019
  • Chemistry
contestada

What is the ph of pure water at 40.0°c if the kw at this temperature is 2.92 × 10-14?

Respuesta :

Edufirst
Edufirst Edufirst
  • 03-04-2019

Answer: pH = 6.77

Explanation:

1) Chemical equilibrium

  • 2 H₂O (l) ⇄ H₃O⁺ (aq) + OH⁻ (aq)

2) Equilibrium constant, Kw

  • Kw = [H₃O⁺] × [OH⁻]
  • By stoichiometry [H₃O⁺] = [OH⁻]. Call it x
  • Kw = x²
  • x² = 2.92 × 10⁻¹⁴ M²
  • x = √ (2.92 × 10⁻¹⁴) = 1.709 × 10⁻⁷ M = [H₃O⁺]

3) pH

  • pH = - log [H₃O⁺] = - log (1.709 × 10⁻⁷) = 6.77
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