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Acids and Alkalis

Examples of Alkalis.

The three common alkalis you will find in the laboratory are

1) Sodium Hydroxide solution - NaOH(aq).
 2) Calcium Hydroxide solution - Ca(OH)2(aq), (lime water)
(Lime water is used in the test for carbon dioxide).

3) Ammonia solution - NH3(aq).

1 and 2 are strong alkalis, 3 is a weak alkali - see pH.
They all ionise in water to form hydroxide ions (OH- ions).

1) NaOH(aq)   arrow     Na+(aq)    +      OH-(aq)

2) Ca(OH)2(aq)   arrow     Ca2+(aq)    +      2OH-(aq)

3) NH3(aq)  +   H2O(l)    reversible arrow    NH4+(aq)   +   OH-(aq)
 NH4+ is an ammonium ion.

Any metal oxide or hydroxide is a base.
If the base dissolves in water it is called an alkali.

(compare this with non-metal oxides).

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