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Acids and Bases 221
Don’t Forget!
H and H 3O represent the same chemical species.
The first reaction goes to completion—there is no HCl left in solution. The second
reaction is an equilibrium reaction—there are appreciable amounts of both
reactants and products left in solution.
There are generally only two strong bases to consider—the hydroxide ion and
those species that produce hydroxide ion in aqueous solution. All other bases
are weak. Weak bases also establish an equilibrium system, as in aqueous solutions
of ammonia:
NH 3(aq) H 2O(l) K OH (aq) NH 4 (aq)
Strong acids include: Strong bases include:
Chloric acid, HClO3 Alkali metal (Group IA) hydroxides
Hydrobromic acid, HBr (LiOH, NaOH, KOH, RbOH and CsOH)
Hydrochloric acid, HCl Calcium, strontium, and barium hydroxides
Hydroiodic acid, HI
Nitric acid, HNO3 Perchloric acid, HClO4 Sulfuric acid, H2SO4 15-3 K w—the Water Dissociation
Constant
Water is amphoteric. It will act as either an acid or a base, depending upon
whether the other species is a base or acid. In pure water, we find the same amphoteric
nature. In pure water, a very small amount of proton transfer is taking place:
H 2O(l) H 2O(l) K H 3O (aq) OH (aq)
This is commonly written as: H 2O(l) K H (aq) OH (aq)
There is an equilibrium constant, called the water dissociation constant, K w,
that describes this equilibrium:
K w [H 3O ] [OH ] 1.00 10 14 at 25 o C