The decrease in the acid dissociation constant from Ka1 to Ka3 tells us that each successive
proton is harder to remove. Consequently, H3PO4 is a stronger acid than
H2PO4
–, and H2PO4
– is a stronger acid than HPO4
2–.
Strong and Weak Bases Just as the acidity of an aqueous solution is a measure of
the concentration of the hydronium ion, H3O+, the basicity of an aqueous solution
is a measure of the concentration of the hydroxide ion, OH–. The most common
example of a strong base is an alkali metal hydroxide, such as sodium hydroxide,
which completely dissociates to produce the hydroxide ion.