5 Steps to a 5 AP Chemistry 2019

(^80) › STEP 4. Review the Knowledge You Need to Score High
Acid–Base Reactions
In general, acids react with bases to form a salt and, usually, water. The salt will depend
upon which acid and base are used:
+→+
+→+
+→
HCl(aq) NaOH(aq) HO(l)NaCl(aq)
HNO(aq) KOH(aq)HO(l) KNO(aq)
HBr(aq) NH(aq) NHBr(aq)
2
323
34
Reactions of this type are called neutralization reactions.
The first two neutralization equations are represented by the same net ionic equation:
H+−(aq)+→OH (aq) HO 2 (l)
In the third case, the net ionic equation is different:
H++(aq)+→NH 34 (aq) NH (aq)
As mentioned previously, certain salts have acid–base properties. In general, salts containing
cations of strong bases and anions of strong acids are neither acidic nor basic. They are neutral,
reacting with neither acids nor bases. An example would be potassium nitrate, KNO 3. The
potassium comes from the strong base KOH and the nitrate from the strong acid HNO 3.
Salts containing cations not of strong bases but with anions of strong acids behave as
acidic salts. An example would be ammonium chloride, NH 4 Cl:
+→++
+−+→+
2NHCl(aq)Ba(OH)(aq)BaCl(aq)2NH(aq) 2HO(l)
NH(aq)OH(aq)NH(aq)HO(l)
42232
432
Cations of strong bases and anions not of strong acids are basic salts. An example would
be sodium carbonate, Na 2 CO 3. It reacts with an acid to form carbonic acid, which would
then decompose to carbon dioxide and water:
2 HCl(aq) + Na 2 CO 3 (aq) → 2 NaCl(aq) + H 2 CO 3 (aq)
↓
CO 2 (g) + H 2 O(l)
2 H+(aq) + CO 32 - → H 2 CO 3 (aq) → CO 2 (g) + H 2 O(l)
The same type of reaction would be true for acid carbonates, such as sodium bicarbonate,
NaHCO 3.
Another group of compounds that have acid–base properties are the hydrides of the
alkali metals and of calcium, strontium, and barium. These hydrides will react with water
to form the hydroxide ion and hydrogen gas:
+→ +
+→+−++
NaH(s)HO(l) NaOH(aq) H(g)
NaH(s)HO(l) Na (aq) OH(aq) H(g)
22
22
Note that in this case, water is behaving as H+OH-.
Acid–Base Titrations
A common laboratory application of acid–base reactions is a titration. A titration is a
laboratory procedure in which a solution of known concentration is used to determine
the concentration of an unknown solution. For strong acid/strong base titration systems,
the net ionic equation is:
H+−(aq)+→OH (aq) HO 2 (l)