Page 138 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 8] CHEMICAL EQUATIONS 127

In double-replacement reactions, the charges on the metal ions (and indeed on nonmetal ions if they do not
form covalent compounds) generally remain the same throughout the reaction.

EXAMPLE 8.14. Complete and balance the following equations. If no reaction occurs, indicate that fact by writing “NR”.
(a) FeCl 3 + AgNO −→ (b) FeCl 2 + AgNO −→
3 3
Ans. (a) FeCl 3 (aq) + 3 AgNO (aq) −→ Fe(NO 3 ) 3 (aq) + 3 AgCl(s)
3
(b) FeCl 2 (aq) + 2 AgNO (aq) −→ Fe(NO 3 ) 2 (aq) + 2 AgCl(s)
3
2+
3+
3+
(a) If you start with Fe , you wind up with Fe .(b) If you start with Fe , you wind up with Fe .
2+
NH 4 OH and H 2 CO 3 are unstable. If one of these products were expected as a product of a reaction, either
NH 3 plus H 2 OorCO 2 plus H 2 O would be obtained instead:
NH 4 OH −→ NH 3 + H 2 O H 2 CO 3 −→ CO 2 + H 2 O

Combustion Reactions
Reactions of elements and compounds with oxygen are so prevalent that they may be considered a separate
type of reaction. Compounds of carbon, hydrogen, oxygen, sulfur, nitrogen, and other elements may be burned.
Of greatest importance, if a reactant contains carbon, then carbon monoxide or carbon dioxide will be produced,
depending upon how much oxygen is available. Reactants containing hydrogen always produce water on burning.
SO 2 and NO are other products of burning in oxygen. (To produce SO 3 requires a catalyst in a combustion reaction
with O 2 .)

EXAMPLE 8.15. Complete and balance the following equations:

(a)C 4 H 8 + O 2 (limited amount) −→ (b)C 4 H 8 + O 2 (excess amount) −→
Ans. (a)C 4 H 8 + 4O 2 −→ 4CO + 4H 2 O (b)C 4 H 8 + 6O 2 −→ 4CO 2 + 4H 2 O
If sufficient O 2 is available (6 mol O 2 per mole C 4 H 8 ), CO 2 is the product. In both cases, H 2 O is produced.

Acids and Bases
Generally, acids react according to the rules for replacement and double-replacement reactions given above.
They are so important, however, that a special nomenclature has developed for acids and their reactions. Acids
were introduced in Sec. 6.4. They may be identified by their formulas that have the H representing hydrogen
written first, and by their names that contain the word acid. An acid will react with a base to form a salt and
water. The process is called neutralization. Neutralization reactions will be used as examples in Sec. 11.3, on
titration.
HNO 3 + NaOH −→ NaNO 3 + H 2 O
A salt
The driving force for such reactions is the formation of water, a covalent compound.
As pure compounds, acids are covalent. When placed in water, they react with the water to form ions; it
is said that they ionize. If they react 100% with the water, they are said to be strong acids. The seven common
strong acids are listed in Table 8-3. All the rest are weak; that is, the rest ionize only a few percent and largely
stay in their covalent forms. Both strong and weak acids react 100% with metal hydroxides. All soluble metal
hydroxides are ionic in water.

Table 8-3 The Seven Common Strong Acids

HCl, HClO 3 , HClO 4 , HBr, HI, HNO 3 ,H 2 SO 4 (first proton only)