Page 146 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 9] NET IONIC EQUATIONS 135

This equation may be interpreted to mean that any soluble silver salt will react with any soluble ionic chloride
to produce (insoluble) silver chloride.

EXAMPLE 9.1. Write three equations that the preceding net ionic equation can represent.
Ans. The following equations represent three of many possible equations:
AgNO + NaCl −→ NaNO 3 + AgCl(s)
3
AgClO + KCl −→ KClO 3 + AgCl(s)
3
AgC H 3 O 2 + NH 4 Cl −→ NH 4 C 2 H 3 O 2 + AgCl(s)
2
Obviously, it is easier to remember the net ionic equation than the many possible overall equations that it represents.
(See Problem 9.12.)

Net ionic equations may be written whenever reactions occur in solution in which some of the ions originally
present are removed from solution or when ions not originally present are formed. Usually, ions are removed
from solution by one or more of the following processes:

1. Formation of an insoluble ionic compound (Table 8-2)
2. Formation of molecules containing only covalent bonds
3. Formation of new ionic species
4. Formation of a gas (a corollary of 2)

Examples of these processes include
−
+
1. AgClO + NaCl −→ AgCl(s) + NaClO 3 Ag + Cl −→ AgCl(s)
3
−
2. HI + NaOH −→ H 2 O + NaI H + OH −→ H 2 O
+
+
Cu + 2Ag −→ Cu 2+ + 2Ag
3. Cu + 2 AgNO −→ 2Ag + Cu(NO 3 ) 2
3
4. NH 4 CO 3 + 2 HCl −→ CO 2 + H 2 O + 2NH 4 Cl CO 3 2− + 2H −→ CO 2 + H 2 O
+
The question arises how the student can tell whether a compound is ionic or covalent. The following
generalizations will be of some help in deciding:
1. Binary compounds of two nonmetals are covalently bonded. However, strong acids (Table 8-3) in water form
ions completely.
2. Binary compounds of a metal and nonmetal are usually ionic.
3. Ternary compounds are usually ionic, at least in part, except if they contain no metal atoms or ammonium
ion.
EXAMPLE 9.2. Predict which of the following will contain ionic bonds: (a) NiCl 2 ,(b)SO 2 ,(c)Al 2 O 3 ,(d)NH 4 NO 3 ,
(e)H 2 SO 4 ,(f ) HCl, and (g) NCl 3 .
Ans. (a) NiCl 2 ,(c)Al 2 O 3 , and (d)NH 4 NO 3 contain ionic bonds. NH 4 NO 3 also has covalent bonds within each ion. (e)
H 2 SO 4 and (f ) HCl would form ions if allowed to react with water.

When do we write compounds as separate ions, and when do we write them as complete compounds? Ions
can act independently in solution, and so we write ionic compounds as separate ions only when they are soluble.
We write compounds together when they are not ionic or when they are not in solution.

EXAMPLE 9.3. Write each of the following compounds as it should be written in an ionic equation. (a) KCl, (b) BaSO 4 ,
(c)SO 2 , and (d) Ca(HCO 3 ) 2 .