The Foundations of Chemistry

Many common food and household
products are acidic (orange juice,
vinegar, soft drink, citrus fruits) or
basic (cleaning preparations, baking
soda).

132 CHAPTER 4: Some Types of Chemical Reactions

Organic acids are discussed in Chapter 27. Some naturally occurring organic weak acids

are tartaric acid (grapes), lactic acid (sour milk), and formic acid (ants). Carbonic acid,

H 2 CO 3 , and hydrocyanic acid, HCN(aq), are two common acids that contain carbon but

that are considered to be inorganicacids. Inorganic acids are often called mineral acids

because they are obtained primarily from nonliving sources.

EXAMPLE 4-1 Strong and Weak Acids

In the following lists of common acids, which are strong and which are weak? (a) H 3 PO 4 ,

HCl, H 2 CO 3 , HNO 3 ; (b) HClO 4 , H 2 SO 4 , HClO, HF.

Plan

We recall that Table 4-5 lists the common strong acids. Other commonacids are assumed

to be weak.

Solution

(a) HCl and HNO 3 are strong acids; H 3 PO 4 and H 2 CO 3 are weak acids.

(b) HClO 4 and H 2 SO 4 are strong acids; HClO and HF are weak acids.

You should now work Exercises 17 and 19.

3 Reversible Reactions

Reactions that can occur in both directions are reversible reactions.We use a double

arrow ( 34 ) to indicate that a reaction is reversible.What is the fundamental difference

between reactions that go to completion and those that are reversible? We have seen that

the ionization of HCl in water is nearly complete. Suppose we dissolve some table salt,

NaCl, in water and then add some dilute nitric acid to it. The resulting solution contains

Na
and Clions (from the dissociation of NaCl) as well as H
and NO 3 (from the

ionization of HNO 3 ). The H
and Clions do notreact significantly to form nonion-

ized HCl molecules; this would be the reverse of the ionization of HCl.

H
(aq)
Cl(aq)88nno reaction

In contrast, when a sample of sodium acetate, NaCH 3 COO, is dissolved in H 2 O and

mixed with nitric acid, the resulting solution initially contains Na
, CH 3 COO, H
, and

NO 3 ions. But most of the H
and CH 3 COOions combine to produce nonionized

molecules of acetic acid, the reverse of the ionization of the acid. Thus, the ionization of

acetic acid, like that of any other weak electrolyte, is reversible.

H
(aq)
CH 3 COO(aq) 34 CH 3 COOH(aq) (reversible)

4 Strong Bases, Insoluble Bases, and Weak Bases

Most common bases are ionicmetal hydroxides. Strong basesare soluble in water and

are dissociated completely in dilute aqueous solution. The common strong bases are listed

H 3 C C (aq) (aq)

O

OH

H 3 CC

O

O

H
(aq)

Inorganic acids may be strong or weak.

Na
and NO 3 ions do not combine
because NaNO 3 is a soluble ionic
compound.

Solutions of bases have a set of
common properties due to the OH
ion. These are described in Section
10-4.

Other organic acids have other groups
in the position of the H 3 CXgroup in
acetic acid.