Topic 12.1.3 Ionic product of water (Kw)

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Created by
Sophie Grainger

Cards (10)

  • Pure water has a slight electrical conductivity, so it must contain some ions. It self-ionises according to the following equation : H2O (l) ⇌ H+ (aq) + OH- (aq).
  • H2O (l) is not included in the Kw expression, because it is a constant at a given temperature. However, H2O (g) is included.
  • Water slightly dissociates to form hydroxide and hydrogen ions as an equilibrium with its own equilibrium constant (Kw).
  • Kw = [H+][OH-]
  • Kw is also known as the ionic product of water.
  • The value of Kw at 25 degrees C (298K) is 1.0 x 10^-14. However, this value changes as temperature changes.
  • Pure water has a pH of 7.00.
  • A neutral solution is defined as one in which the hydrogen ion concentration is equal to the hydroxide ion concentration. Pure water is a neutral solution.
  • pKw = -log Kw and Kw = 10 ^-pKw
  • For a strong base, the concentration of OH- will be the same as the concentration of the base.