5 Steps to a 5 AP Chemistry

Reactions of this type are called neutralization reactions.

The first two neutralization equations are represented by the same net ionic equation:

In the third case, the net ionic equation is different:

As mentioned previously, certain salts have acid–base properties. In general, salts con-

taining 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.

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:

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 titrationis 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:

For example, suppose you wanted to determine the molarity of an HCl solution.

You would pipet a known volume of the acid into a flask and add a couple drops of a suit-

able acid–base indicator. An indicator that is commonly used is phenolphthalein, which is

Haq OHaq HOl+()+→−() 2 ()

NaHs HOl NaOHaq H g

Na H s H O l Na a

() () ( ) ( )

() () (

+→ +

+→+

22

2 qqOHaqHg)()()++

−

2

↓

22 NH Cl aq 42232 () ( )()+→++Ba OH aq BaCl aq()NH aq() 2 H O(ll

NH aq OH aq NH aq H O l

)

43 +()+→+−() () 2 ()

Haq NHaq NHaq++()+→ 34 () ()

Haq OHaq HOl+()+→−() 2 ()

78  STEP 4. Review the Knowledge You Need to Score High