The Foundations of Chemistry

Mn 2 O 7 (
) 
H 2 O(
)88n2[H
(aq)
MnO 4 (aq)]

manganese(VII) oxide permanganic acid

2CrO 3 (s) 
H 2 O(
)88n[2H
(aq)
Cr 2 O 72 (aq)]

chromium(VI) oxide dichromic acid

Neither permanganic acid nor dichromic acid has been isolated in pure form. Many stable

salts of both are well known.

The halides and oxyhalides of some nonmetals hydrolyze (react with water) to produce

two acids: a (binary) hydrohalic acid and a (ternary) oxyacid of the nonmetal. Phosphorus

trihalides react with water to produce the corresponding hydrohalic acids and phospho-

rous acid, a weak diprotic acid, whereas phosphorus pentahalides give phosphoric acid and

the corresponding hydrohalic acid.

PX 3 
3H 2 O(
)88nH 3 PO 3 (aq)
3HX(aq)

PX 5 
4H 2 O(
)88nH 3 PO 4 (aq)
5HX(aq)

There are no changes in oxidation numbers in these reactions. Examples include the reac-

tions of PCl 3 and PCl 5 with H 2 O.

PCl 3 (
) 
3H 2 O(
)88n H 3 PO 3 (aq) 
3[H
(aq)
Cl(aq)]

phosphorus phosphorous acid

trichloride

PCl 5 (s) 
4H 2 O(
)88n H 3 PO 4 (aq) 
5[H
(aq)
Cl(aq)]

phosphorus phosphoric acid

pentachloride

A drop of PCl 3 is added to water
that contains the indicator methyl
orange. As PCl 3 reacts with water to
form HCl and H 3 PO 3 , the indicator
turns red, its color in acidic solution.

392 CHAPTER 10: Reactions in Aqueous Solutions I: Acids, Bases, and Salts

 7 
 7

 6 
 6

 3

 5

 3

 5

 3 
 3

 5 
 5

Key Terms

Acid (Arrhenius or Brønsted–Lowry) A substance that pro-
duces H
(aq) ions in aqueous solution. Strong acids ionize
completely or almost completely in dilute aqueous solution;
weak acids ionize only slightly.
Acid anhydride The oxide of a nonmetal that reacts with water
to form an acid.
Acidic salt A salt that contains an ionizable hydrogen atom; does
not necessarily produce acidic solutions.
Amphiprotism The ability of a substance to exhibit amphoter-
ism by accepting or donating protons.
Amphoterism Ability of a substance to act as either an acid or
a base.
Anhydrous Without water.
Autoionization An ionization reaction between identical mole-
cules.

Base (Arrhenius) A substance that produces OH(aq) ions in

aqueous solution. Strong bases are soluble in water and are com-

pletely dissociated.Weak bases ionize only slightly.

Basic anhydride The oxide of a metal that reacts with water to

form a base.

Basic salt A salt containing a basic OH group.

Brønsted–Lowry acid A proton donor.

Brønsted–Lowry base A proton acceptor.

Conjugate acid–base pair In Brønsted–Lowry terminology, a

reactant and product that differ by a proton, H
.

Coordinate covalent bond A covalent bond in which both

shared electrons are furnished by the same species; the bond

between a Lewis acid and a Lewis base.

Dissociation In aqueous solution, the process in which a solid

ionic compoundseparates into its ions.