Predicting Reaction Products

Free Response Section of the AP Chemistry Exam

• Question 4: (10 % of Section Score)

• 3 Reaction Predictions- Must give a balanced chemical equation- Must write the equation in net ionic form- Must answer one question about the reaction

Successfully Predicting Reaction Products

• Know the list of Common Ions• Knowledge of Nomenclature• Know how to use SRP Table• Learn the Solubility Rules• Know the Reaction Classifications• Write net ionic equations

Classification of Reactions• Acid/Base• Precipitation• Hydrolysis• Decomposition (& reversed)• Ligands• REDOX• Organic

Acid/Base Reactions

HX + MOH ----> MX + HOH

Acid/Base Reaction Sample #1

1991 (c) equal volumes of 0.1-molar sulfuric acid and 0.1-molar potassium hydroxide are mixed.

Acid/Base Sample #2 1998 (d) Equal volumes of equimolar solutions of phosphoric acid and

potassium hydroxide are mixed.

Precipitation Reactions

One or more products is(are) not significantly soluble in water. CuSO4 and BaOH

Generally both reactants are salts in solution AX + BY -----> AY + BX

Where AY and/or BX is (are) insoluble in water

Net ionic equation:

A+ + Y- -----> AY

Where AY is insoluble in water & BX is soluble in water

Precipitation Reactions Sample #1

2003B (d) A solution of lead(II) nitrate is added to a solution of potassium sulfate.

Precipitation Reactions Sample #2

2002 (a) A solution of sodium iodide is added to a solution of lead(II) acetate.

Hydrolysis Reactions• Generally three types:

– A metal oxide reacts with water to form a base.– A nonmetal oxide reacts with water to form an acid.– A metal hydride reacts with water to form a base &

hydrogen gas.

Hydrolysis Reaction Sample #1

2002 (c) Solid cesium oxide is added to water.

Hydrolysis Reaction Sample #2

2003 (h) solid dinitrogen pentoxide is added to water.

Hydrolysis Reaction Sample #3

1995 (g) Solid calcium hydride is added to distilled water.

Decomposition Reactions

A lone compound is strongly heated, exposed to strong sunlight or electric current.

Decomposition Reactions

Compounds that readily decompose:– Metallic carbonates– Most metallic hydroxides– Metallic chlorates– Metallic sulfites– Some acids– Peroxides– Electrolysis of salts

Decomposition Reaction Sample # 1

1996 (a) Solid calcium carbonate is strongly heated.

Decomposition Reaction Sample #2

Solid calcium hydroxide is strongly heated.

Decomposition Reaction Sample #3

Solid potassium chlorate is strongly heated.

Decomposition Reaction Sample #4

1998 (e) Solid calcium sulfite is heated in a vacuum.

Decomposition Reaction Sample #5

Decomposition Reaction Sample #6

Decomposition Reaction Sample #7

Decomposition Reaction Sample #8

Molten magnesium bromide is electrolyzed using inert electrodes.

Ligand Reactions Ligand reactions involve the reaction between

ligands and some metal anions (Fe, Cu, Pb, Ag, Au, Sn, Pt, Co, etc).

Learn the common ligands: CN-, SCN-, NO2

- , NH3, H2O, OH-, halides (F-, Cl-, Br-, I-)

Ligand Reactions General rule: The number of ligands attached to the

metallic anion is usually DOUBLE the cation’s charge.

Ag+ → Ag(NH3)2+

Cu2+ → Cu(NH3)42+

Fe3+ → Fe(NH3)63+

Ligand Reactions Sample #1

2003 (e) Excess concentrated aqueous ammonia is added to solid silver chloride.

Ligand Reactions Sample #2

1989 (f) A solution of ammonium thiocyanate is added to a solution of iron(III) chloride.

REDOX Reactions• These are reactions that involve CHANGES in

oxidation state.• Learn the list of important oxidizers and reducers

from the handout.

REDOX ReactionsSample #1

2003 (f) Magnesium ribbon is burned in oxygen.

REDOX ReactionsSample #2

2003 (g) A bar of strontium metal is immersed in a 0.1 M copper(II) nitrate solution.

REDOX ReactionsSample #3

2001 (f) Chlorine gas is bubbled through a solution of potassium

bromide.

REDOX ReactionsSample #4

2002 (g) Acidified solutions of potassium permanganate and iron(II) nitrate are mixed together.

REDOX ReactionsSample #5

2001 (e) A solution of iron(II) chloride is added to an acidified solution of

sodium dichromate.

REDOX ReactionsSample #6

1993 (a) A strip of copper is immersed in dilute nitric acid

Organic Reactions• Reactions involving compounds containing

hydrogen, carbon, and sometimes other nonmetal elements.

• Learn the hydrocarbon nomenclature and common functional groups.

Organic Reactions Sample #1

2003B (c) Propanone is burned in air

Organic ReactionsSample #2

1982 (e) Methane gas is heated with an excess of chlorine gas.

Organic ReactionsSample #3

1986 (g) ethene (ethylene) gas is bubbled through a solution of bromine.

Organic ReactionsSample #4

1985 (c) Ethanol and formic acid (methanoic acid) are mixed and warmed.