The Foundations of Chemistry

highways and in the emergency treatment of cardiac arrest. Several ammonium salts are
used as fertilizers. Many organic acids (carboxylic acids) and their derivatives occur in
nature. Acetic acid is present in vinegar; the sting of an ant bite is due to formic acid.
Amino acids are the building blocks of proteins, which are important materials in the
bodies of animals, including humans. Amino acids are carboxylic acids that also contain
basic groups derived from ammonia. The pleasant odors and flavors of ripe fruit are due
in large part to the presence of esters (Chapter 27), which are formed from the acids in
unripe fruit.

PROPERTIES OF AQUEOUS SOLUTIONS

OF ACIDS AND BASES

Aqueous solutions of most protonic acids (those containing acidic hydrogen atoms)
exhibit certain properties, which are properties of hydrated hydrogen ions in aqueous solu-
tion.

1.They have a sour taste. Pickles are usually preserved in vinegar, a 5% solution of

acetic acid. Many pickled condiments contain large amounts of sugar so that the

taste of acetic acid is partially masked by the sweet taste of sugar. Lemons contain

citric acid, which is responsible for their characteristic sour taste.

2.They change the colors of many indicators (highly colored dyes). Acids turn blue

litmus red, and cause bromthymol blue to change from blue to yellow.

3.Nonoxidizing acids react with metals above hydrogen in the activity series (Section

4-8, part 2) to liberate hydrogen gas, H 2. (HNO 3 , a common oxidizing acid, reacts

with metals to produce nitrogen oxides, not H 2 .)

4.They react with (neutralize) metal oxides and metal hydroxides to form salts and

water (Section 4-9, part 1).

5.They react with salts of weaker or more volatile acids to form the weaker or more

volatile acid and a new salt.

6.Aqueous solutions of acids conduct an electric current because they are totally or

partly ionized.

10-1

Caution: We should nevertry to

identify a substance by taste. You have,

however, probably experienced the

sour taste of acetic acid in vinegar or

citric acid in foods that contain citrus

fruits.

10-1 Properties of Aqueous Solutions of Acids and Bases 373

Left,Many common household liquids are acidic, including soft drinks, vinegar, and fruit
juices. Right,Most cleaning materials are basic.