Equation Notes
I WILL make you do these over and over again. You may thank me on May 7th. A card will do, but I
prefer donuts.
I. Types of reactions that you will encounter:
Trick-a-licious
1. metathesis (double replacement)
2. single replacement
3. combustion
4. acid/base neutralization
5. addition/synthesis
6. decomposition
7. reactions of anhydrides
8. redox
9. complex ion formation
H2CO3 always goes to CO3 and H2O.
Ammonia solution is NH4OH
MgCO3 always decomposes to MgO and CO2
H2O2 decomposes to H2O and O2
II. General Rules
1. All reactions go—single replacement reactions all react.
2. All equations should be written in net ionic form.
Ionized
Not Ionized
Strong Acids
Weak Acids
Strong Bases
Weak Bases
Soluble Salts
Insoluble Salts
Gases
Solids
3. Solubility Rules
Soluble
Group I and NH4+
Nitrates
Acetates
Chlorides (except HAP)
Not Soluble
Carbonates (except Group I and NH4+)
Phosphates (except Group I and NH4+)
Chromates, Oxides and Sulfides (except Group I, NH4+)
Hydroxides ((except Group I and NH4+, Ca, Sr, and Ba)
4. Oxidation Numbers
1. the oxidation number of an element is 0
2. the oxidation number of monoatomic ion is equal to its charge
3. in compounds:
the oxidation number of hydrogen is +1 (except in metal hydrides where it is -1)
the oxidation number of oxygen is -2 (except in peroxides where it is -1)
the oxidation number of alkali metals is +1
the oxidation number of alkaline earth metals is +2
the oxidation number of terminal halogens is -1
4. the sum of all the oxidation numbers in a molecule or ion is equal to the charge.
III. Metathesis reactions
1. begin with two reactant compounds and produce two product compounds. They typically occur when the
reactants are acids, bases or salts.
2. The products are predicted by simply switching the positive parts of the two reactants.
a. Ionized hydrochloric acid mixed with sodium hydroxide
HCl + NaOH → NaCl + HOH (or H2O)
H + OH-  HOH [net-ionic]
b. Not ionized acetic acid mixed with potassium hydroxide
CH3COOH + KOH → KCH3COO + H2O
-
-
CH3COOH + OH → CH3COO + H2O [net-ionic]
IV. Single replacement
1. reactions are a reaction in which an element reacts with a compound. In that compound there must
be an element similar in some way to the reacting element but less reactive.
Calcium hydroxide mixed with hydrochloric acid
CaO + 2 HCl → CaCl2 + H2O [molecular]
+
2+
CaO + 2 H → Ca + H2O [net-ionic]
Magnesium metal is treated with weak hydrochloric acid
Mg + 2HCl  MgCl2+ H2 [molecular]
+
2+
Mg + 2 H → Mg + H [ionic]
2
2. TrickstersAmmonium chloride plus sodium hydroxide
NH4Cl + NaOH →NH4OH + NaCl [molecular] NH4OH always breaks down to NH3 + H2O
+
-
NH4 + OH → NH3 + H2O [net-ionic]
Sodium carbonate mixed with hydrochloric acid
Na2CO3 + 2 HCl → H2CO3 + 2 NaCl [molecular] H2CO3 always breaks down to CO2 + H2O
2-
+
CO3 + 2 H → CO2 + H2O [net-ionic]
V. Combustion
1. Oxygen is always a reactant.
2. Hydrocarbon -, the simple rule is that burning (combining with O2) always produces carbon dioxide
and water.
Hexane is burned in air
2 C6H14 + 19 O2 → 12 CO2 + 14 H2O [molecular and ionic equation]
3. metal sulfides are the reactants in combustion reactions. In these cases the sulfide is generally
converted to the metal oxide and sulfur dioxide:
Copper II Sulfide is burned in air.
CuS + O2→ CuO + SO2
VI. Acid/Base Neutralization
1. Acids react with bases to produce salts and water.
2. Strong acids and strong bases ionize completely.
Sulfuric acid is neutralized with sodium hydroxide
H2SO4 +2 NaOH  Na2SO4 + 2H2O [molecular]
2H+ + 2OH-  2H2O [net ionic]
3. Strong and a weak
Acetic acid is mixed with sodium hydroxide
HC2H3O2 + NaOH  Na C2H3O2 + HOH [molecular]
HC2H3O2 + OH-  C2H3O2- + HOH [net ionic – shows some HC2H3O2 ionizes, but not the
majority]
VII. Synthesis
1. Two or more elements or substances combine to form one product.
Lithium metal is burned in nitrogen gas
Li + N2  Li3N [molecular and net ionic]
Sulfur dioxide gas is passed over solid calcium oxide
SO2 + CaO  CaSO3 [molecular and net ionic]
VIII. Decomposition
1. One reactant breaking down into two or more elements, two or more compounds or an element and a
compound.
Molten sodium chloride is electrolyzed.
2NaCl(l) 2Na + Cl2
A solution of hydrogen peroxide is decomposed catalytically.
H2O2  H2O + O2
Solid magnesium carbonate is heated.
MgCO3  MgO + CO2
Solid potassium chlorate is heated
2KClO3  2KCl + 2O2
IX. Anhydride
1. Anhydride means without water
2. Water is a reactant in all of these equations
3. Nonmetallic oxides (acidic anhydrides) plus water yield acids.
Carbon dioxide is bubbled into water.
CO2 + H2O  H2CO3
Metallic oxides (basic anhydrides) plus water yield bases.
Solid sodium oxide is added to water.
Na2O + H2O  Na+ + OHMetallic hydrides (ionic hydrides) plus water yield metallic hydroxides and hydrogen gas.
Solid sodium hydride is added to water.
NaH + H2O  Na+ + OH- + H2
X. Redox
1. Redox reactions involve the transfer of electrons. The oxidation numbers of at least two elements
must change.
2. Single replacement, some combination and some decomposition reactions are redox reactions.
3. To predict the products of a redox reaction, look at the reagents given to see if there is both an
oxidizing agent and a reducing agent.
4. When a problem mentions an acidic or basic solution, it is probably redox.
Common oxidizing agents
Products formed
MnO4- in acidic solution
Mn2+
MnO2 in acidic solution
Mn2+
MnO4 in neutral or basic solution
MnO2(s)
2Cr2O7 in acidic solution
Cr3+
HNO3, concentrated
NO2
HNO3, dilute
NO
H2SO4, hot, concentrated
SO2
metal-ic ions
metal-ous ions
Common reducing agents
sulfite ions or SO2
nitrite ions
C2O42 -
Products formed
sulfate ions
nitrate ions
CO2
A solution of tin(II) chloride is added to an acidified solution of potassium permanganate.
Sn2+ + H+ + MnO4-  Sn4+ + Mn2+ + H2O
A solution of potassium iodide is added to an acidified solution of potassium dichromate.
I- + H+ + Cr2O72-  Cr3+ + I2 + H2O
Hydrogen peroxide solution is added to a solution of iron(II) sulfate.
H2O2 + Fe2+  Fe3+ + H2O
A piece of iron is added to a solution of iron(III) sulfate.
Fe + Fe3 + Fe2+
XI. Complex Ions
1. Complex ion- the combination of a central metal ion and its ligands
2. Ligand- group bonded to a metal ion
3. Coordination compound- a neutral compound containing complex ions
4. Addition reactions formed like this:
Formed from:
(Al or Al(OH)3 or Al3++ OH-)
Complex ion
[Al(OH)4]-
Name
tetrahydroxoaluminate ion
(Ag+ + NH3)
[Ag(NH3)2]+
diamminesilver(I) ion
(Zn(OH)2 + OH-)
[Zn(OH)4] 2-
tetrahydroxozincate ion
(Zn2+ + NH3)
[Zn(NH3)4] 2+
tetramminezinc ion
(Cu2+ + NH3)
Cu(NH3)4]2+
tetramminecopper(II) ion
(Fe3+ + SCN-)
[FeSCN] 2+
thiocyanoiron(III) ion
5. Decomposition reactions – an acid to a complex ion breaks it up.