Acids and Alkalis
What is the Difference between Strong and Weak Alkalis?
and acids can be described as
strong or weak.
This does not mean the same as concentrated or dilute.
The strength of an alkali (or acid)
on how ionised it is in water.
An alkali forms hydroxide ions (OH- ions) in water.
What is a Strong Alkali?
A strong alkali is completely
An example of a strong alkali is sodium hydroxide.
A strong alkali has a pH of 14.
ion + hydroxide ion
NaOH(aq) Na+(aq) + OH-(aq)
hydroxide exists only as ions
both as a solid and
dissolved in water (see examples of other strong alkalis).
What is a Weak Alkali?
partly (less than 100%)
An example of a weak alkali is ammonia.
A weak alkali has a pH of 11 or 12.
ammonia + water ammonium ion + hydroxide
NH3(g) + H2O(l) NH4+(aq) + OH-(aq)
Some of the ammonia molecules become ions in water
but most of them stay as molecules.
Ammonia in water makes ammonium hydroxide solution
(NH4OH(aq)). This is also called ammonia solution.
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