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LEMBAR PEMBELAJARAN 3

Autoionization of Water

Using sensitive instruments, pure water is observed to weakly
conduct electricity, indicating the presence of very small

concentrations of ions. They arise from the very slight self-
ionization, or autoionization, of water itself, represented by the

following equilibrium equation.

The forward reaction requires a collision of two H2O molecules.

The constant of the product of water ions,

Since water is a pure liquid, with a constant 55.6 molar

concentration, it does not appear in this equilibrium law.
Because of the importance of the autoionization equilibrium, its

equilibrium constant is given the special symbol, Kw, that is
called the ion product constant of water.

Often, for convenience, we omit the water molecule that
carries the hydrogen ion and write H+ in place of H3O+. The
equilibrium equation for the autoionization of water then

simplifies to

Bahasa Inggris Kimia (PKIM3139) 29