AP Chemistry
I.
Equation Writing Categories and Examples
Non-aqueous reactions
A Synthesis – Two elements (or compounds) combine to make one complex molecule most often
through a redox reaction. If water is involved, the reaction does have to be written net-ionic.
A. 2 elements → binary compound (result can be ionic or covalent)
o 2Na + Cl2→ 2NaCl
B. element + compound → larger covalent compound
o nonmetal oxide (or halide) + oxygen (or additional halide) → higher oxide (or halide)
 2SO2 + O2 → 2SO3
C. compound + compound → larger compound
o metallic oxide + nonmetallic oxide → ionic compound (polyatomic ion)
 Li2O + CO2 → Li2CO3
o metallic oxide + water → base (hydroxide)
 BaO + H2O → Ba+2 + 2OHo nonmetallic oxide + water → acid (oxidation state in nonmetal usually remains same)
 SO3 + H2O → 2H+ + SO4-2
Examples of synthesis reactions:
 calcium metal is heated strongly in the presence of oxygen. Which of the
reactants undergoes oxidation?
ans: 2Ca + O2 → 2CaO; Ca
 solid lithium oxide is exposed to a stream of carbon dioxide gas. Does
carbon dioxide exhibit polarity?
ans: Li2O + CO2 → Li2CO3; CO2 is nonpolar
 dinitrogen pentoxide gas is bubbled into water. Describe the pH of the
solution relative to 7.
ans: N2O5 + H2O → 2H+ + 2NO3-. The pH of system is less than 7
(acidic).
 nitrogen monoxide gas is heated in the presence of oxygen. Is the oxygen
gas in this reaction oxidized or reduced. Explain.
ans. 2NO + O2 → 2NO2. The oxygen’s oxidation state goes from 0
to -2. It is reduced.
B Decomposition (by heat) – One substance breaks apart to make two simpler substances.
A. metallic carbonate → metallic oxide + carbon dioxide
o BaCO3 → BaO + CO2
B. metallic chlorate → metallic chloride + oxygen
o 2KClO3 → 2KCl + 3O2
C. metallic hydroxide → metallic oxide + water
o Mg(OH)2 → MgO + H2O
D. oxyacids → nonmetallic oxide + water
o H2CO3 → CO2 + H2O
E. decomposition by electrolysis (water or binary molten ionic compound)
o MgCl2 → Mg + Cl2
Examples of decomposition reactions:
 solid calcium carbonate is heated. Identify a substance with calcium
carbonate as its primary ingredient.
ans: CaCO3 → CaO + CO2. Chalk, limestone, marble
 water is decomposed by electrolysis. Which product is formed at the
cathode?
ans: 2H2O → 2H2 + O2. H2 – reduction at the cathode
 magnesium chlorate is placed in a crucible and heated. Would an acid that
contains the ClO3- ion be strong or weak? Explain.
ans: Mg(ClO3)2 → MgCl2 + 3O2. The acid would be strong (HClO3).
Two or more oxygens versus ionizable hydrogens.
C. Combustion (hydrocarbons)
A. Hydrocarbon + oxygen → carbon dioxide + water (complete combustion)
B. Hydrocarbon + oxygen → carbon + carbon monoxide + carbon dioxide + water
(incomplete combustion)
Hydrocarbons:
CH4 = methane, CH3OH = methanol
C2H6 = ethane, C2H5OH = ethanol, C2H4 = ethene, C2H2 = ethyne
C3H8 = propane, C3H7OH = propanol, C3H6 = propene, C3H4 = propyne
C4H10 = butane, C4H9OH = butanol
C5H12 = pentane, C5H11OH = pentanol
C6H14 = hexane, C6H13OH = hexanol
alkanes = CnH2n+2
alkenes = CnH2n
alkynes = CnH2n-2
Example of a combustion reaction:
 propanol is completely burned in air. How would the products change if
incomplete combustion occurred?
ans: C3H7OH + 9/2O2 → 3CO2 + 4H2O. C and CO as well as CO2.
II.
Aqueous reactions
A Single Replacement – More reactive element takes the place of the less active element in the
compound. The less active element is ‘replaced’. These reactions always involve changes in
oxidation number. The words below represent the molecular description of the reactions.
The net ionic reactions will often look different than the word description. Remember,
spectator ions are not included in the net ionic equation.
A. active metal + water → hydrogen gas + metallic hydroxide
o 2Na + 2H2O → H2 + 2Na+ + 2OHB. metal + acid → hydrogen gas + salt of the acid
o Zn + 2H+ → H2 + Zn+2
C. active metal + compound → less active metal + new compound
o Fe + Pb+2 → Fe+2 + Pb
D. halogen + compound → less active halogen + new compound
o Cl2 + 2Br- → Br2 + 2Cl-
Examples of single replacement reactions
 calcium metal is added to a dilute solution of hydrochloric acid. Identify the
spectator ion(s) in the reaction.
ans: Ca + 2H+ → Ca+2 + H2. Cl liquid bromine is added to a solution of potassium iodide. What is the color
of liquid bromine?
ans: Br2 + 2I- → I2 + 2Br-. Brown.
 small chunks of potassium are added to water. What is the flame test color
of excited potassium?
ans: 2K + H2O → H2 + 2K+ + 2OH-. Purpleish.
B. Double Replacement – Two reactant compounds produce two product compounds. Driving
force behind double replacement reactions is the formation of a precipitate, acid/base
neutralization, or formation of a gas (watch for H2SO3, H2CO3, or NH4OH as products).
Remember, the net-ionic equations will look different than the molecular equations.
A. precipitation reaction – Two solutions mixed, precipitate forms (know solubility table to
predict this.
o Ag+ + Cl- → AgCl
B. acid/base neutralization reaction: acid + base → salt + water (must know strong and
weak acids and bases.
o H+ + OH- → H2O (strong acid and strong base)
o If acid is weak acid, it will be written molecularly on the left and its anion will be
involved on the right
C. formation of a gas (watch for H2SO3, H2CO3, or NH4OH as products; metallic carbonates,
sulfites, and sulfides as reactants)
Common Gas Products:
H2SO3 → H2O + SO2
H2CO3 → H2O + CO2
NH4OH → H2O + NH3
H2S (from the DR reaction)
Examples of double replacement reactions:
 sulfuric acid is added to a solution of barium acetate. Why does the resulting
solution have poor conductivity compared to the reactants?
ans: 2H+ + SO4-2 + Ba+2 + 2C2H3O2- → BaSO4 + 2HC2H3O2 . Both
products exhibit poor solubility in water, thus very little ions, very little
conductivity.
 solutions of sodium phosphate and calcium chloride are mixed. When a calcium
chloride solution is made, describe the change in heat that occurs.
ans: 3Ca+2 +2 PO4-3 → Ca3(PO4)2. When calcium chloride dissolves in
water, the solution is exothermic (gets warmer).


a solution of hydrochloric acid is mixed with solid potassium sulfite. List the
spectator ion(s) in the reaction.
ans: 2H+ + K2SO3 → H2O + SO2 + 2K+. Cl is the spectator ion.
solutions of lithium hydroxide and hydrobromic acid are mixed. How does the
size of the bromide ion compare to the chloride ion on the periodic table?
ans: OH- + H+→ H2O. Br- is bigger than Cl-.
C. Complexation Reactions – Reactions involving transition metal ions or compounds (and also Al)
and a source of ligands, which are groups that donate both electrons to the metal (to make a
coordination bond). Common ligands to watch out for are the hydroxide ion, ammonia molecule,
and the cyanide ion (but there are others). The key to such reactions is recognizing words such
as “concentrated” or “excess” in the reaction description. Those words indicated that enough
of the complexing agent has been added to eliminate the possibility of precipitating a lessercoordinated species. Most often, a general rule of thumb is that you will add the number of
ligands to the metal that would equal twice its charge. Look at the examples below.
common ligands:
Ligand
H2O
NH3
OHClCN-
Name
aqua
ammine
hydroxyl
chloro
cyano
- Watch out for words such as “concentrated” and “excess”
- Add the number of ligands equal to twice the charge of the metal
Examples of complexation reactions:
 a concentrated solution of ammonia is added to a solution of copper (II)
chloride. What is the color of complex ion solution formed?
ans: 4NH3 + Cu+2 → Cu(NH3)4+2. Dark purple.
 excess concentrated potassium hydroxide is added to a precipitate of zinc
hydroxide. Identify the Lewis Acid in the reaction.
ans: 2OH- + Zn(OH)2 → Zn(OH)4-2. The Zn+2 is the Lewis Acid.
 an excess of ammonia gas is bubbled through a solution saturated with silver
chloride. What is the color of silver chloride?
ans: 2NH3 + AgCl → Ag(NH3)2+ + Cl-. White.
D. Non-trivial Redox Reactions – These are reactions that are more than the run-of-the-mill single
replacement and synthesis reactions. These reactions follow simple rules. You should know the
common oxidizing/reducing pairs (see tip sheet as well as below) as well as follow the following
rules…
a. Elements in their highest positive oxidation states (same as group #, whether A or B groups)
can ONLY be reduced.
b. Elements in their lowest oxidation states (0 for metals, negative for non-metals, based upon
distance from noble gas) can ONLY be oxidized.
c. If the mixture is acidic, H+ should be included as reactant; water is a product
d. If the mixture is basic, OH- is a reactant, water is a product.
Common Oxidizing Agents
Nitrate (nitric acid), NO3Permanganate, MnO4Hydrogen peroxide, H2O2
Dichromate/chromate, Cr2O7-2,
CrO4-2
Iodate, IO3Standard state halogens
Sulfate (sulfuric acid), SO4-2
Common Reducing Agents
-
Hydrogen peroxide, H2O2
Sulfite, SO3Hydrogen gas, H2
Free Metals, Mo
Iodide, I-
Reduced To
NO (dilute acid), NO2
(concentrated)
Mn+2 (acid)
H2O
Cr+3 (acid)
IHalide ions
SO2
Oxidized To
O2
SO4-2
H+
M+
I2
We will focus more attention on the nontrivial redox reaction when we balance redox
reactions in the electrochemistry unit. Until then, I will recommend that you try to
memorize these matching pairs.
III.
Organic Reactions – Below are examples of the most common organic reactions that appear on
the AP Test. It will be very difficult to do an organic reaction unless you know a little background
information. You should know the following information:
 General formulas for alkanes, alkenes, alkynes, and alcohols (see above).
 Prefixes that tell you the number of carbon atoms in the chain (see above).
 Some common functional groups and how they attach to the carbon chain.
This will be covered later in the year
 Fundamental naming schemes (We will cover this throughout the year).
With the above mentioned, below are three common organic reactions that we encounter:
A. combustive oxidation of hydrocarbons (already discussed above)
B. addition reactions that occur over a double bond (most often)
o C3H6 + Cl2 → C3H6Cl2
C. substitution reactions, where a hydrogen atom in the molecule is “displaced” by
something.
o CH4 + Br2 → CH3Br + HBr
Examples of organic reactions:
 A sample of 2-butene is treated with hydrogen bromide gas. What does the 2
indicate in the name 2-butene?
Ans: C4H8 + HBr → C4H9Br. The 2 is the numbered carbon where the
double bond is first found.
 An excess of chlorine gas is added to ethyne gas. What is the color of chlorine
gas?
Ans: C2H2 + 2Cl2 → C2H2Cl4. Pale green.
 Methane is mixed with excess bromine gas. At standard temperature and
pressure, what is the phase of elemental bromine?
Ans: CH4 + 2Br2 → CBr4 + 2H2. Liquid.