Reaction Notes for AP Chemistry

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PREDICTING REACTIONS AP STYLE

You will write a net ionic equation given a description of the reactants. One point is awarded for writing the correct reactants and two points for writing the correct products. Remember to write reactants and products in net ionic form. You do not need to balance the equation. In all cases a reaction does occur.

KNOW:
bulletNomenclature
bulletSolubility rules
bulletWhich elements are diatomic

A. Double displacement.

bullet Precipitation → forming an insoluble product
bullet Neutralization → acid + base à salt + water
bullet Gas forming → carbonic acid in solution forms water and carbon dioxide and sulfurous acid will decompose into water and sulfur dioxide
bullet If a nonelectrolyte is formed from a double displacement reaction a reaction occurs. Phosphorus halides react with water to produce an acid of phosphorus (phosphorous acid or phosphoric acid) and a binary acid containing a halogen. Group I&II nitrides react with water to produce the metallic hydroxide and ammonia

Examples:

Aqueous solutions of silver nitrate and sodium iodide are mixed

Ag+(aq) + I-(aq) à AgI(s)

Solid aluminum chloride is added to an aqueous solution of potassium chromate

AlCl3(s) + CrO4(aq)à Al2(CrO4)3(s)

solutions of hydrochloric acid and sodium hydroxide are mixed

H+(aq) + OH-(aq) à H2O(l)

Acetic acid reacts with solid potassium hydroxide

CH3COOH(aq) + KOH(s) à CH3COO-(aq) + H2O(l) + K+

Hydrofluoric acid reacts with solid silicon dioxide.

HF + SiO2 à SiF4 + H2O

phosphorus tribromide is added to water

PBr3 + H2O à H3PO3 + H+ + Br-

calcium carbonate crystals are added to a solution of hydrochloric acid

CaCO3(s) + H+(aq) à H2O(l) + CO2(g) + Ca2+(aq)

excess hydrochloric acid solution is added to a solution of potassium sulfite

H+ + SO32- à H2O + SO2

B. Single displacement (replacement) are also be redox : → A more reactive element can displace a less reactive element with similar properties in a compound. (metals displace metals and nonmetals displace nonmetals)

Examples:

zinc metal reacts with tin (II) sulfate solution

Zn(s) + Sn2+(aq) à Sn(s) + Zn2+(aq)

chlorine gas reacts with sodium bromide solution

Cl2(g) + Br-(aq) à Br2 + Cl-(aq)

potassium reacts with water

K + H2O à KOH + H2

magnesium turnings are added to a solution of iron(III) chloride

Mg + Fe3+ à Fe + Mg2+

C. Combination or synthesis → two reactants result in a single product
bulletMetal oxide + water à metallic hydroxide (base)
bulletNonmetal oxide + water à nonbinary acid
bulletMetal oxide + nonmetal oxide à nonbinary salt

Examples :

solid calcium oxide is added to water

CaO(s) + H2O(l) à Ca(OH)2(aq) ( mosttext consider calcium hydroxide as a strong base but on some AP test it was treated as a weak base)

Sulfur dioxide gas is bubbled through water

SO2(g) + H2O(l) à H2SO3(aq)

Powdered magnesium oxide is added to a container of carbon dioxide

MgO(s) + CO2(g) à MgCO3(s)

D. Decomposition → one reactant becomes several products
bullet Metallic hydroxide à metal oxide + water
bullet Nonbinary acid à nonmetal oxide + water
bullet Nonbinary salt à metal oxide + nonmetal oxide
bullet Metallic chlorates à metallic chlorides + oxygen
bullet Electrolysis decompose compound into elements (water in dilute acids or solutions of dilute acids)
bullet Hydrogen peroxide à water + oxygen
bullet Metallic carbonates à metal oxides + carbon dioxide
bullet Ammonium carbonate à ammonia, water and carbon dioxide.

Examples:

a current of electricity is passed through water

H2O à H2 + O2

Potassium chlorate is heated

KClO3 à KCl + O2

Hydrogen peroxide is catalytically decomposed

H2O2 à H2O + O2

Calcium carbonate is heated

CaCO3 à CaO + CO2

Sulfurous acid decomposes

H2SO3 à H2O + SO2

Magnesium hydroxide decomposes

Mg(OH)2 à MgO + H2O

E. Hydrolysis → compound reacting with water.

bullet Watch for soluble salts that contain anions of weak acid (the anion is a conjugate base) and cations of weak bases (the cation is a conjugate acids).

Examples:

1.0 M sodium acetate is added to water

CH3COO-  +  H2O à CH3COOH(aq) + OH-(aq)

Solid ammonium chloride is added to water

NH4Cl + H2O à NH3(aq) + H3O+(aq) + Cl-(aq)

F. Reactions of coordinate compounds and complex ions Remember ligands are bonded (coordinate covalent) to a central atom that is usually a transitional metal ion. The most frequently occurring ligands are hydroxide and ammonia. Review coordinate compound nomenclature. The number of ligands attached to the central ion is often twice the oxidation number of the central metal ion.

bullet Complex formation by adding excess source of ligand to transitional metal of highly charged metal ion such as Al3+
bullet Breakup of complex by adding an acid à metal ion and the species formed when hydrogen from the acid reacts with the ligand
bullet Keywords such as "excess" and "concentrated" of compounds containing common ligands indicates formation of a complex ions. AgNO3 + HCl forms the white precipitate, AgCl. with excess, concentrated HCl, the complex ion AgCl2- will form.

Examples:

tetraammine copper II ions are reacted with nitric acid

H+ +Cu(NH3)42+ à NH4+ + Cu2+

A concentrated solution of ammonia is added to a solution of copper(II) chloride.

Cu2+ + NH3 à Cu(NH3)42+

G. Lewis acid base reactions → formation of coordinate covalent bond

Example:

The gases boron trifluoride and ammonia are mixed

BF3 + NH3à BF3NH3

H. redox → change in oxidation state → a reaction between a oxidizer and a reducer.

Recognized:
bulletFamiliarization with important oxidizers and reducers
bullet"added acid" or "acidified"
bulletan oxidizer reacts with a reducer of the same element to produce the element at intermediate oxidation state
bulletWhen the hydrides of an alkali metal (Family 1), Ca, Ba, or Sr dissolve in water, hydroxides will form and H2 gas is released.

OXIDIZERS:

MnO4- in acid Mn2+
MnO2 in acid Mn2+
MnO4- in neutral or basic solution MnO2
Cr2O72- in acid Cr3+
HNO3 concentrated NO2
HNO3 dilute NO
H2SO4, hot, concentrated SO2
Metal ic ions Metal ous ions
Halogens diatomic Halide ions
Na2O2 NaOH
HClO4 Cl-
H2O2 H2O

REDUCERS:

Halide ions Halogens
Metal element Metal ion
Sulfite Sulfate
Nitirite Nitrate
Halogen element in dilute basic solution Hypohalite ion an halide ion
Halogen element in concentrated basic solution Halite ion
Metal ous ion Metallic ion
H2O2 O2
C2O42- CO2

Examples:

magnesium metal is added to dilute nitric acid

Mg + H+ + NO3- à Mg2+ + NO + H2O

Solution of iron (II) nitrate is added to an acidified solution of potassium permanganate

Fe2+ + MnO4- + H+ à Mn2+ + Fe3+ + H2O

Solutions of potassium iodide, potassium iodate and dilute sulfuric acid are mixed

I- + IO3- + H+ à I2 + H2O

A piece of iron is added to a solution of iron (III) sulfate

Fe + Fe3+ à Fe2+

Solid lithium hydride is placed in water

LiH + H2O à Li+ + OH- + H2

I. Combustion → results in forming the oxide of the elements of the compound
bullet Hydrocarbons or alcohols combine with oxygen to form carbon dioxide and water.
bullet Ammonia combines with limited oxygen to produce NO and water and with excess oxygen to produce NO2 and water.
bullet Nometallic hydrides combine with oxygen to form oxides and water.
bullet Nonmetallic sulfides combine with oxygen to form oxides and sulfur dioxide.

Examples:

gaseous silane, SiH4, is burned in oxygen.

SiH4 + O2 à H2O + SiO2

carbon disulfide vapor is burned in excess oxygen.

CS2 + O2 à CO2 + SO2

ethanol is burned completely in air.

C2H5OH + O2 à  CO2 + H2O