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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) is called lime water
(lime water is used in the test for carbon dioxide gas).

3) Ammonia solution - NH_3(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)              Na⁺_(aq)    +      OH^-_(aq)

2) Ca(OH)_2(aq)            Ca²⁺_(aq)    +     2OH^-_(aq)

3) NH_3(aq)  +   H₂O_(l)        NH₄⁺_(aq)   +   OH^-_(aq)
NH₄⁺ is called 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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