5 Steps to a 5 AP Chemistry

Salts containing the following ions are normally insoluble:

 Most carbonates (CO 32 −) and phosphates (PO 43 −) are insoluble,except those of Group IA

and the ammonium ion.

 Most sulfides (S^2 −) are insoluble,except those of Group IA and IIA and the ammonium ion.

 Most hydroxides (OH−) are insoluble,except those of Group IA, calcium, and barium.

 Most oxides (O^2 −) are insoluble,except for those of Group IA, and Group IIA which react

with water to form the corresponding soluble hydroxides.

Let’s see how one might apply these rules. Suppose a solution of lead(II) nitrate is mixed

with a solution of sodium iodide. Predict what will happen.

Write the formulas:

Convert to the ionic form:

Predict the possible products by combining the cation of one reactant with the anion

of the other and vice versa:

Apply the solubility rules to the two possible products:

PbI 2 (s) Insoluble, therefore a precipitate will form.

NaNO 3 (aq) Soluble, no precipitate will form.

Complete the chemical equation and balance it:

If both possible products are soluble, then the reaction would be listed as NR

(No Reaction). In the reaction question part of the AP exam, there will be a possible reac-

tion for every part of the question. If at least one insoluble product is formed, the reaction

is sometimes classified as a double displacement (replacement)or metathesis reaction.

Oxidation–Reduction Reactions

Oxidation–reduction reactions, commonly called redox reactions,are an extremely impor-

tant category of reaction. Redox reactions include combustion, corrosion, respiration,

photosynthesis, and the reactions involved in electrochemical cells (batteries). The driving

force involved in redox reactions is the exchange of electrons from a more active species to

a less active one. You can predict the relative activities from a table of activities or a half-

reaction table. Chapter 16 goes into depth about electrochemistry and redox reactions.

The AP free-response booklet includes a table of half-reactions, which you may use for

help during this part of the exam. A similar table can be found in the back of this book.

Alternatively, you may wish to memorize the common oxidizing and reducing agents.

Redox is a term that stands for reduction and oxidation. Reductionis the gain of elec-

trons and oxidationis the loss of electrons. For example, suppose a piece of zinc metal is

Pb^2 +−()aq +→ 2 I aq()PbI s 2 ()

Pb NO( 32 )()aq +→+ 22 NaI aq()PbI s 2 ()NaNO aq 3 ()

PbI 23 +NaNO

Pb aq^2 +−+−()+++→ 2 NO aq 3 ()Na aq() ()I aq

Pb NO( 32 )()aq +→NaI aq()

Reactions and Periodicity  71

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