The Foundations of Chemistry

CH 3 COOH
H 2 O 34 H 3 O

CH 3 COO

Hence, the CH 3 COOion is a stronger base than the NO 3 ion, but it is still weak.
In dilute solutions, strong acids and strong bases are completely ionized or dissociated.
In the following sections we consider dilute aqueous solutions of salts. Based on our clas-
sification of acids and bases, we can identify four different kinds of salts.

1.Salts of strong bases and strong acids

2.Salts of strong bases and weak acids

3.Salts of weak bases and strong acids

4.Salts of weak bases and weak acids

SALTS OF STRONG BASES AND STRONG ACIDS

We could also describe these as salts that contain the cation of a strong base and the anion
of a strong acid. Salts derived from strong bases and strong acids give neutralsolutions
because neither the cation nor the anion reacts appreciably with H 2 O. Consider an aqueous
solution of NaCl, which is the salt of the strong base NaOH and the strong acid HCl.
Sodium chloride is ionic even in the solid state. It dissociates into hydrated ions in H 2 O.
H 2 O ionizes slightly to produce equal concentrations of H 3 O
and OHions.

H 2 O

NaCl (solid)8888nNa

Cl

100%

H 2 O
H 2 O 34 OH
H 3 O

We see that aqueous solutions of NaCl contain four ions, Na
, Cl, H 3 O
and OH.
The cation of the salt, Na
, is such a weak acid that it does not react appreciably with
water. The anion of the salt, Cl, is such a weak base that it does not react appreciably
with water. Solutions of salts of strong bases and strong acids are therefore neutralbecause
neither ion of such a salt reacts to upset the H 3 O
/OHbalance in water.

SALTS OF STRONG BASES AND WEAK ACIDS

When salts derived from strong bases and weak acids are dissolved in water, the resulting
solutions are always basic. This is because anions of weak acids react with water to form
hydroxide ions. Consider a solution of sodium acetate, NaCH 3 COO, which is the salt of
the strong base NaOH and the weak acid CH 3 COOH. It is soluble and dissociates
completely in water.

Acetate ion is the conjugate base of a weakacid, CH 3 COOH. Thus, it combines to some
extent with H 3 O
to form CH 3 COOH. As H 3 O
is removed from the solution, causing

NaCH 3 COO(solid) Na
 
 CH 3 COO

CH 3 COOH 
 H 2 O

OH 
 H 3 O

(result is excess OH)

H 2 O

100%

H 2 O
H 2 O

Equilibrium is shifted

18-8

18-7

18-8 Salts of Strong Bases and Weak Acids 777

See the Saunders Interactive

General Chemistry CD-ROM,

Screen 17.10, Acid–Base Properties of

Salts.

Salt of

strong base/strong acid

Neutral

aqueous solution

Salt of

strong base/weak acid

Basic

aqueous solution

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