Green Chemistry and the Ten Commandments

Exercise: Give the formulas and names of compounds formed from each cation on the
top row with each anion on the bottom row, below:

1. NH 4 +^ 2. Ca2+^ 3. Al3+
   (A) Cl- (B) SO 42 - (C) PO 43 -

Answers: 1(A) NH 4 Cl, ammonium chloride; 1(B) (NH 4 ) 2 SO 4 , ammonium sulfate; 1(C),
(NH 4 ) 3 PO 4 , ammonium phosphate; 2(A) CaCl 2 , calcium chloride; 2(B) CaSO 4 , calcium
sulfate; 2(C), Ca 3 (PO 4 ) 2 , calcium phosphate; 3(A) AlCl 3 , aluminum chloride; 3(B)
Al 2 (SO 4 ) 3 , aluminum sulfate; 3(C), AlPO 4 , aluminum phosphate.

Prefixes are used in naming ionic compounds where more than 1 cation or more than
1 anion are present in the formula unit. For example, Na 2 HPO 4 in which each formula unit
is composed of 2 Na+ ions, 1 H+
ion, and 1 PO 43

-

ion is called disodium monohydrogen

phosphate. And KH 2 PO 4 is called monopotassium dihydrogen phosphate.

3.10. Acids, Bases, and Salts

Other than binary molecular compounds, most inorganic compounds can be
classified as acids, bases, or salts. These three categories of compounds and their names
are addressed briefly here.

Acids

Acids are characterized by the H+ ion, the presence of which in water, makes the
water acidic. An acid either contains this ion or produces it when it dissolves in water.
Sulfuric acid, H 2 SO 4 , is an example of a compound that contains H+ ion. Dissolved in
water, a molecule of sulfuric acid exists as 2 H+ ions and 1 SO 42 - ion. An example of
a compound that is classified as acidic because it produces H+ ion when it dissolves in
water is carbon dioxide, which undergoes the following reaction in water solution:

CO 2 + H 2 O → H+ + HCO 3 - (3.10.1)

In this case, only a small fraction of the CO 2 molecules dissolved in water undergo
the above reaction to produce H+ so water solutions of CO 2 are weakly acidic and
carbon dioxide is classified as a weak acid. It is the presence of dissolved CO 2 from the
carbon dioxide naturally present in air that makes rainfall coming from even nonpolluted
atmospheres slightly acidic and, as discussed in Chapter 7, the weakly acidic properties
of CO 2 are very important in natural waters in the environment. Other acids, such as
hydrochloric acid, HCl, are completely dissociated to H+ and an anion (in the case of
HCl the Cl-^ anion) when they are dissolved in water; such acids are strong acids.
The naming of acids follows certain rules. In the case of an acid that contains only
H and one other element, the acid is a hydro-ic acid. So HCl is called hydrochloric acid.

74 Green Chemistry, 2nd ed