Page 91 - Instant notes

C3
FURTHER ACIDS AND BASES

Key Notes
Strong acids completely dissociate into their conjugate base and
hydronium ions. Strong bases completely dissociate into their
conjugate acid and hydroxide ions. For weak acids and bases,
incomplete dissociation occurs and an acid-base equilibrium is
established.
The equilibrium constant for the dissociation of a weak acid is
called the acid dissociation constant or acidity constant, K a . The
equilibrium constant for the dissociation of a weak base is called
the base dissociation constant or basicity constant, K b . The acid
dissociation constant of an acid is linked to the base dissociation
constant of its conjugate base by the equation K a K b =K w . pK a and
pK b are a measure of the acid and base strength with lower values
meaning increased strength. pK a and pK b correspond to the pH
and pOH values respectively when the acid and conjugate base
activities are equal. A strong acid results in a very weak
conjugate base and a strong base results in a very weak conjugate
acid.
Acid dissociation constants can be used to predict whether a salt
solution will be acidic or basic. Salts often consist of an acid (the
positive ion) and a base (the negative ion). If the pK a of the acid
is less than the pK b of the base, then the solution will be acidic. If
the converse is true, the solution will be basic.
A polyprotic acid is an acid that can donate more than one proton.
Acid dissociation can generally be considered to be a number of
stepwise single proton dissociation reactions, each with their own
acid dissociation constant. Combining these stepwise constants
produces the multiproton acid dissociation constant. Multiproton
base dissociation reactions (for a polyprotic base) can also be
considered to be a succession of single proton base dissociation
reactions.
Related topics Fundamentals of equilibria Electrochemistry and ion
(C1) concentration (E5)
Ions in aqueous solution
(E1)

Strong and weak acids and bases

A strong acid is an acid for which complete dissociation can be assumed to occur,
forming the hydronium ion and the conjugate base. A good example is: