The Ammonium hydroxide reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Ammonium hydroxide

Ammonium hydroxide (NH₄OH) is the name given to a molecule formed by the dissolution of ammonia in water. Since ammonia ionizes to a small extent, ammonium and hydroxide ions will be present in an aqueous solution of ammonia. It is sometimes convenient to refer to these ions as "ammonium hydroxide". However this is a wrong way of describing the ionisation. Instead, the following equation based on Bronsted-Lowry Theory should be used.

NH₃ + H₂O ↔ NH₄⁺ + OH^-

With a base-ionization constant (K_b) of 1.8×10^-5, in a 1M ammonia solution, about 0.4% of the ammonia will be ionized.

Ammonium hydroxide was an attempt by chemists to apply Arrhenius theory which did not seem to work earlier as Ammonia does not have any hydroxide ions ( which Arhennius said was required for a substance to have alkaline properties ).

Modern chemical analysis shows that hydroxide ions are rarely found in solution. Bronsted-Lowry theory completely explains this phenomena without the introduction of this axiom, as shown in the above reaction, in which water acts as a base. Also see conjugate acid-base pairs.

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