Base (chemistry)

The common (Arrhenius) definition of a base, also known as an alkaline compound, is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium ion (H3O) concentration in water, whereas bases reduce this concentration. Arrhenius bases are water-soluble and these solutions always have a pH greater than 7.

Neutralization of acids

When dissolved in water, sodium hydroxide decomposes into hydroxide and sodium ions:

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:mbox{NaOH} o mbox{Na}^++mbox{OH}^-

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and similarly, hydrochloric acid forms hydronium and chloride ions:

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:mbox{HCl} o mbox{H}^++mbox{Cl}^-.

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When the two solutions are mixed, the H+ and OH− ions combine to form water molecules:

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:mbox{H}^++mbox{OH}^- ombox{H}_2mbox{O}.

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If equal amounts of NaOH and HCl (measured in moles, not grams) are dissolved, the base and the acid exactly neutralize, leaving only NaCl (table salt) in solution.

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