AP Chemistry
Last Update: 9/24/2013

Previous AP Chemistry exams…
 consistently had several multiple choice problems
requiring you to predict the products of a
reaction.
 always had a free response problem on chemical
reactions

The new AP Chemistry exam (spring 2014)
 will probably still emphasize chemical reactions
(no one is really sure what’s going to be on the
exam)
A solution of copper (II) sulfate is
spilled onto a sheet of freshly
polished aluminum metal.
Description
Nomenclature
Reaction
Conditions
Formula of
Reactants
CuSO4 + Al  ?
Type of Reaction
Element + Ionic Compound =
Single Replacement
Reaction Pattern
A + BC  AC + B
Products
Balanced Chemical Reaction
CuSO4 + Al  Cu + Al2(SO4)3
3 CuSO4 +2 Al  3 Cu + Al2(SO4)3

Certain key words and chemicals allow you
to identify a reaction.
 For each type of reaction, these key
words/chemicals will be listed as “You just
might have a _____ reaction if…”
 This is blatant piracy from Jeff Foxworthy’s skit
“You just might be a redneck if…”
▪ This was the equivalent of Chuck Norris facts in the
early 1990’s.


Play external video clip now
http://www.youtube.com/watch?v=_WAQGD
a9pJ8

You just might have a double replacement reaction
if…
 both reactants are soluble ionic compounds or
 the reactants are a solube ionic compound and an acid.


Pattern:
Examples:
AB + CD  AD + CB
 A solution of copper (II) chloride is added to a solution of
sodium sulfide.
▪ CuCl2+ Na2S  CuS + 2 NaCl
 Solutions of strontium nitrate and sodium sulfate are
mixed
▪ Sr(NO3)2 + Na2SO4  SrSO4 + 2 NaNO3
Fire at the Caribbean Company Oil Storage Depot (2009)
Source: news.bbc.co.uk Week in Pictures (downloaded 10/23/2009)


You just might have a combustion reaction if…
 the problem includes words like “burned” or “heated”; and
 the reactant is an organic compound, H2, a metal, P4, or S8.
General Pattern: AB + O2  AO + BO
 In general, the products are all oxides (H2O, CO2, Al2O3, SO2,

SO3, P4O10)
Examples:





Methane is burned in air: CH4 + 2 O2  CO2 + 2 H2O
Butane is burned in air: 2 C4H10 + 13 O2  8 CO2 + 10 H2O
White phosphorous is heated in air:
P4 + 5 O2  P4 O10
Magnesium ribbon is heated in air:
2 Mg + O2  2 MgO
note: ionic compounds do not burn when heated
 If ionic compounds are heated, then it is most likely a
decomposition reaction

You might have a single replacement reaction if…
 the reactants are an element and a compound.

General Patterns:
 if the element is a metal (M):
M + BC  MC + B
 if the element is a non-metal (X): X + BC  BX + C

Examples:
 Liquid bromine is shaken with a 0.5 M sodium iodide solution.
▪ Br2 + 2 NaI  2 NaBr + I2
 A strip of magnesium metal is added to a solution of silver
nitrate.
▪ Mg + 2 AgNO3  Ag + Mg(NO3)2
 Zinc metal powder is poured into a beaker of hydrochloric acid.
▪ Zn + 2 HCl  H2 + ZnCl2


You just might have an acid-base reaction if…
 the reactants are an acid and a base.
 acids: H+, NH4+, or H2O
 bases (B): OH-, O2-, CO32-, HCO3-, S2-, NH3, or H2O
General Pattern: HA + MB  MA + HB
 Often, the reaction produces an ionic compound called a salt
 there are a lot of exceptions, depending on the base
▪ Acid + OH- H2O + salt
▪ Acid + O2-  salt with OH- as the anion
▪ Acid + CO32- or HCO3- CO2 + H2O + salt
▪ Acid + S2-  H2S (smells like rotten eggs) + salt
▪ Acid + NH3  salt with NH4+ as the cation
 When H2O acts as an acid it produces OH When H2O acts as a base, it produces H+

Chemistry Joke: What does this mean?
NaCl
NaOH





Solutions of potassium hydroxide and acetic acid are
mixed.
 KOH + HC2H3O2  H2O + KC2H3O2
Calcium oxide powder is added to distilled water.
 CaO + H2O  Ca(OH)2
Solid lead (II) carbonate is added to a 0.5 M solution of
sulfuric acid
 PbCO3 + H2SO4  CO2 + H2O + PbSO4
An excess of hydrochloric acid is added to solid zinc
sulfide.
 2 HCl + ZnS  ZnCl2 + H2S
Ammonia is added to a solution of phosphoric acid.
 3 NH3 + H3PO4  (NH4)3PO4



Play external video clips now
http://www.youtube.com/watch?v=AkRvn0p
XTiw
http://www.youtube.com/watch?v=tZZv5Z2I
z_s

You just might have a combination reaction
if…
 both reactants are elements, or
 two molecules are mixed, or
 carbon dioxide is reacted with an oxide.

General Pattern:
A + B  AB
 multiple reactants  one product
 molecular oxide + water often  an acid
 ionic oxide + CO2  CO32-

Examples:
 Sulfur trioxide gas is bubbled through water.
▪ SO3 + H2O  H2SO4
▪ This reaction is responsible for acid rain
 Solid dinitrogen pentoxide is added to water.
▪ N2O5 + H2O  2 HNO3
 Carbon dioxide is passed over hot, solid sodium oxide:
▪ CO2 + Na2O  Na2CO3
▪ This reaction has been considered as a means of carbon
sequestration.
Source: Wikimedia Commons (downloaded 9/24/2013)

You just might have a decomposition reaction if…





there is only one reactant and
energy is added (light, electricity, or heat); or
a solid ionic compound is heated.
Note: heat can also mean a combustion reaction. The reactants
in a decomposition reaction must not be flammable.
General Pattern: A  B + C





One reactant  multiple products
CO32-  CO2 + O2HCO32-  CO2 + H2O + CO322 H2O2  2 H2O + O2
ClO3-, BrO3-, or IO3-  O2 + Cl-, Br-, or I-

Examples
 Solid sodium hydrogen carbonate is strongly
heated:
▪ 2 NaHCO3  CO2 + Na2CO3 + H2O
 Solid sodium carbonate is strongly heated:
▪ Na2CO3  CO2 + Na2O
 A vial of ammonium sulfide is smashed, producing
a foul smell of rotting organic matter:
▪ (NH4)2S  2 NH3 + H2S

For each of the following lab situations, write
the balanced molecular equation for the
resulting reaction.
1. A strip of zinc is placed in a solution of nickel (II)
nitrate.
2. Ethyne is burned in air.
3. Solid calcium carbonate is added to a solution of
acetic acid.
4. Lithium metal is strongly heated in nitrogen gas.

Due next class:
 Download this PowerPoint from NetClassroom
 Read/review Mr. Tom’s Guide to Chemical
Reactions.
 Predicting Chemical Reactions Worksheet 1

Due on Tuesday
 Predicting Chemical Reactions Worksheet 2
AP Chemistry
Last Update: 9/24/2013
A solution of copper (II) sulfate is
spilled onto a sheet of freshly
polished aluminum metal.
Description
Nomenclature
Reaction
Conditions
Formula of
Reactants
CuSO4 + Al  ?
Type of Reaction
Element + Ionic Compound =
Single Replacement
Reaction Pattern
A + BC  AC + B
Products
Balanced Chemical Reaction
CuSO4 + Al  Cu + Al2(SO4)3
3 CuSO4 +2 Al  3 Cu + Al2(SO4)3
Identifying Factors
Reaction Type and
Pattern
2 ionic compounds or Double Repl.
Ionic + acid
AB + CD  AD + CB
Organic compound
or element is
burned/heated
AB + O2  AO + BO
Element +
Compound
Single Repl.
M + BC  B + MC
X + BC  C + BX
Acids: H+, NH4+, H2O
Bases (B): OH-, O2-,
CO32-, HCO3-, S2-,
NH3, H2O
Acid-Base
H+ is transferred
from acid to base
HA + MBMA + HC
1 reactant + energy
Ionic comp. + energy
Decomposition
AB+C
Identifying Factors
Reaction Type and
Pattern
2 elements or
Combination
2 molecular comp. or A + B  AB
CO + O2-

Coordination compounds/coordination complexes have covalent
bonds between a metal ion and a ligand.
 The metal ion must…
▪ want more electrons and
▪ be able to pull electrons into a bond (high electronegativity).
▪ Transition metal cations (i.e. Cu2+, Co2+, Ni2+) and main group metals (i.e. Pb2+,
Sn4+) have these properties.
 The transition metal is bonded to a ligand.
▪ Any species that has an unshared pair of electrons (NH3, Cl-, H2O)
▪ In order to drive the formation of the coordination bond, the ligand must be
present in large quantities.
▪ The only exception is thiocyanate (SCN-). Even small quantities of thiocyanate can form a
coordination compound.
 Usually several ligands will bond to the metal ion
▪ The number of ligands per metal ion is called the coordination number.
Different colored coordination compounds of Nickel (II)
[Ni(NH3)6]2+
[Ni(en)3]2+
[NiCl4]2-
[Ni(H2O)6]2+
Source: Wikimedia Commons (downloaded 9/24/2013)

You just might have a coordination compound
if…
 You have a metal ion and…
▪ It must be either a main group metal ion or a transition metal
ion.
 You have a ligand and…
▪ Ligands must have a pair of unshaired electrons.
▪ Ligands must either be SCN- or be present in large quantities.
▪ Often words like “concentrated” or “excess” are used.
 The metal and the ligand cannot react in any other
way (i.e. double exchange won’t work).


Skip straight to the net ionic equation.
General pattern: Mx+ + n Ly-  [M(L)n]x-y
 Mx+ = metal ion
 Ly- = ligand
 n = coordination number (usually 2, 4, or 6)
▪ usually you just arbitrarily pick a either 2, 4, or 6
 [M(L)n]x-y = the coordination complex

Excess concentrated ammonia solution is added to a
solution of nickel (II) sulfate.





metal = Ni2+
ligand = NH3
coordination number: 4 (just pick either 2, 4, or 6)
reaction:
4 NH3 + Ni2+  [Ni(NH3)4]2+
Potassium thiocyanate is added to a solution of iron
(III) nitrate.




metal = Fe3+
ligand = SCNcoordination number: 6
reaction:
6 SCN- + Fe3+  [Fe(SCN)6]3-

Excess concentrated hydrochloric acid is added to a solution of 1.0
M cobalt (II) chloride.





try a double exchange rxn: 2 HCl + CoCl2  CoCl2 + 2 HCl
metal = Co2+
ligand = Clcoordination number:
2
4
reaction:
2 Cl- + Co2+  [Co(Cl)2]
4 Cl- + Co2+  [Co(Cl)4]2-
Excess concentrated sodium nitrate is added to a solution of iron
(III) nitrate.




try a double exchange rxn: 3 NaNO3 + Fe(NO3)3  Fe(NO3)3 + 3 NaNO3
metal = Fe3+
ligand = NO3coordination number: 2
6
reaction: 2 NO3- + Fe3+  [Fe(NO3)2]+
6 NO3- + Fe3+  [Fe(NO3)6]3-
+ Energy 


Play external video clip now (heating copper
(II) sulfate.
http://www.youtube.com/watch?v=M6IIbZx7
xvQ

Almost always a dehydration reaction.
 In the solid state, many transition metals form a
hydrated crystal.
 These crystals have water covalently bonded into
their structure.
 These bonds are weak and can be broken with a small
input of energy.
▪ The coordination compound decomposes
▪ This is sometimes called a dehydration reaction
▪ This usually occurs at such high temperature that the water is
released as water vapor.

General Pattern
 Hydrated ionic solid  anhydrous ionic solid +
water
 MA • n H2O (s)  MA (s) + n H2O (g)

Examples:
 Solid copper (II) sulfate pentahydrate is heated.
▪ CuSO4 • 5 H2O  CuSO4 + 5 H2O
 Solid nickel (II) chloride hexahydrate heated.
▪ NiCl2 • 6 H2O  NiCl2 + 6 H2O

You just might have a non-trivial redox reaction
if…
 One of your reactants is a multivalent metal such as
Sn, Mn, Fe, or Cu; or
 One of your reactants is Ag+, Cr2O72-, MnO4-, CO, or
O22-; or
 The reaction happens in solution and the problem
specifies whether the solution is acidic or basic.

Often, with non-trivial redox reactions, you will
be given some of the products.
 The challenge is balancing the reaction.
 Skip straight to the net ionic equation.
Balancing non-trivial redox reactions
1.
Separate the overall reaction into two half-reactions.

In each half-reaction, pair up the elements (i.e. the reactant with Cr is in the
same half-reaction as the product with Cr).
▪
▪
▪
4 substances  1 reactant and 1 product per half reaction
If you do not have enough substances, use the same substance in both reactions.
Substances with just H and O can be alone
Balance all elements except the H and O
Balance O using H2O.
Balance H using H+
Balance charge using e-.
(basic solutions only) For every H+, add an OH- to each side. Combine
H+ + OH-  H2O. Cancel out H2O.
Combine the half-reactions.
2.
3.
4.
5.
6.
7.
1.
2.
3.
Multiply each half-reaction by a coefficient so that the e- cancel out.
Add the two half-reactions to get a net ionic reaction.
Cancel out anything which occurs on both sides.

Examples (full procedure on board)
 Fe2+ + Cr2O72-  Fe3+ + Cr3+
 Cr2O72- + C2O42-  Cr3+ + CO2
 Cu + NO3-  Cu2+ + NO2
 Mn2+ + H2O2  MnO2
(in acid)
(in acid)
(in acid)
(in base)

Simple redox reactions can be broke into halfreactions as well.
 Molecular reaction: M + AB  A + MB
 Net Ionic reaction: M + A+  M+ + A
 Half reactions: M  M+
and A+  A

Example: Magnesium metal is added to a
solution of copper (II) chloride.
 Molecular Reaction: Mg + CuCl2  MgCl2 + Cu
 Net Ionic Reaction: Mg + Cu2+  Mg2+ + Cu
 Half Reactions:
Mg  Mg2+ + 2 e
Cu2+ + 2 e-  Cu
We’re only half way through
today’s presentation!
Identifying Factors
Reaction Type and
Pattern
2 ionic compounds or Double Repl.
Ionic + acid
AB + CD  AD + CB
Organic compound
or element is
burned/heated
AB + O2  AO + BO
Element +
Compound
Single Repl.
M + BC  B + MC
X + BC  C + BX
Acids: H+, NH4+, H2O
Bases (B): OH-, O2-,
CO32-, HCO3-, S2-,
NH3, H2O
Acid-Base
H+ is transferred
from acid to base
HA + MBMA + HC
1 reactant + energy
Ionic comp. + energy
Decomposition
AB+C
Identifying Factors
Reaction Type and
Pattern
2 elements or
Combination
2 molecular comp. or A + B  AB
CO + O2Transition/main grp.
metal + excess
ligand
Coordination
Mx+ + n Ly- 
[M(L)n]x-y
Hydrate is heated
Dehydration
MA • n H2O 
MA + n H2O (g)
Multivalent metal
Ag+, Cr2O72-, MnO4-,
CO or O22Acidic or basic soln.
Non-Trivial Redox
1. Solid tetraphosphorous decoxide is added to
distilled water.
2. Equal volumes of 0.1 M solutions of lead (II)
nitrate and magnesium iodide are combined.
3. Excess concentrated sodium chloride is added to
a solution of tin (II) chloride.
4. What is the coefficient of H+ after the following
reaction is balanced?
▪
Sn2+ + Cr2O72- + H+ Sn4+ + Cr3+ + H2O
5. Iron metal is burnt in a thermic lance.

Due next class:
 Predicting Chemical Reactions Worksheet 2