Answer:
The autoionization of water is:
2H₂O ⇄ H₃O⁺ + OH⁻ Kw
Explanation
2 moles of water can generate hydronium and hydroxide, when they work as an acid or as a base
If we take account that the concentration of protons (hydroniums), at the standard temperature is 1×10⁻⁷ M, it can be considered that the molarity of water is a constant that can be incorporated into a “greater” constant that also includes to Kc and that is known as ionic product of water, Kw. The expression is:
Kw = [H₃O⁺] . [OH⁻] / [H₂O]²
We do not include water → Kw = [H₃O⁺] . [OH⁻]
Since the water dissociation reaction produces the same concentration of H₃O⁺ as OH⁻, [OH⁻] in pure water will also be 1×10⁻⁷ M
Kw = 1×10⁻⁷ . 1×10⁻⁷ = 1×10⁻¹⁴
pKw = pH + pOH
14 = 7 + 7
