Auto ionisation of H₂O leads to the formation of

Water Autoionization: Formation of Ions

Autoionization, also known as self-ionization, is a fundamental chemical process where a solvent, like water, spontaneously ionizes into its constituent ions. In the case of water, this means two water molecules react with each other to form ions.

H₂O Autoionization Process

The autoionization of water involves one water molecule acting as a Brønsted-Lowry acid (donating a proton, ${\mathrm{H}}^{+}$) and another water molecule acting as a Brønsted-Lowry base (accepting that proton).

Here's a step-by-step breakdown of the water autoionization process:

- One ${\mathrm{H}}_2\mathrm{O}$ molecule donates a proton (${\mathrm{H}}^{+}$). When it loses a proton, it forms a hydroxide ion, $\mathrm{O}{\mathrm{H}}^{-}$.
- The other ${\mathrm{H}}_2\mathrm{O}$ molecule accepts this proton (${\mathrm{H}}^{+}$). When it gains a proton, it forms a hydronium ion, ${\mathrm{H}}_3{\mathrm{O}}^{+}$.

Autoionization Chemical Equation

The balanced chemical equation representing the autoionization of H₂O is:

$${\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}(\mathrm{aq})+\mathrm{O}{\mathrm{H}}^{-}(\mathrm{aq})$$

This equation shows that water molecules are in dynamic equilibrium with their conjugate acid (hydronium ion) and conjugate base (hydroxide ion).

Products of Autoionization

From the autoionization reaction, it is clear that the autoionization of ${\mathrm{H}}_2\mathrm{O}$ leads to the formation of two distinct ions:

- **Hydronium ion (${\mathrm{H}}_3{\mathrm{O}}^{+}$): This is formed when a water molecule accepts a proton.
- Hydroxide ion ($\mathrm{O}{\mathrm{H}}^{-}$):** This is formed when a water molecule donates a proton.

These two ions are always present in pure water at any temperature, though their concentrations are very low at room temperature ($1.0\times 10^{-7}$ M for both at 25°C). The product of their concentrations, $[{\mathrm{H}}_3{\mathrm{O}}^{+}][\mathrm{O}{\mathrm{H}}^{-}]$, is known as the ion product of water (${\mathrm{K}}_{\mathrm{w}}$).

Therefore, the autoionization of ${\mathrm{H}}_2\mathrm{O}$ results in the formation of both ${\mathrm{H}}_3{\mathrm{O}}^{+}$ and $\mathrm{O}{\mathrm{H}}^{-}$ ions.