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Acids and Alkalis

The Ionisation of Water.

Why is Water Neutral?

In a sample of water
a very small number of water molecules will form ions.

water              hydrogen ion  +   hydroxide ion.
H₂O_(l)                     H⁺_(aq)            +         OH^-_(aq)

This ionisation is reversible (shown by the arrow).

The hydrogen ion is acidic. The hydroxide ion is alkaline.
Water forms equal amounts of both ions, and so water is neutral.

Compare this reaction with neutralisation.

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