Transcript Rxn Pred students

Reaction Predictions
Rev. 01/23/12
Objectives
 SWBAT
 Review their knowledge of cations/anions, salts,
diatomic molecules, strong acids and bases, solubility
rules and the activity series.
 Review the proper format required to write molecular,
and net ionic equations.
 Practice using Solubility Rules to determine if a
reaction occurs.
New Format
 You will have a reaction prediction quiz every Wed.
until the AP exam.
 The first quiz will be a group quiz (groups of 3)
 The next two quizzes will be pairs.
 The remaining quizzes will be individual.
The AP Way
 Always write net ionic equations.
 Balance the equations.
 There are 3 reaction prediction problems on the exam.
 There is an associated question with each reaction
prediction question.
Most Commonly Used
Cations and Anions

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Hydrogen H+
Sodium Na+
Potassium K+
Calcium Ca+²
Magnesium Mg+²
Iron (Ferrous) Fe+²
Iron (Ferric) Fe+³
•Hydroxide OHˉ
•Chloride Clˉ
•Sulfide Sˉ²
•Bicarbonate HCOзˉ
•Carbonate COзˉ²
•Sulfate SO4ˉ²
•Phosphate PO4ˉ ³
Tip
 Group 1A cations are spectator ions.
Cations/ Anions, contd.
 You can figure out the charge of an ion by using
the periodic table.
 Ex:
 Alkali metals such as Lithium can easily lose an
electron to become stable (just like a Noble gas)
so taking away an electron give Lithium a +1
charge.
 On the other hand Halogens can easily accept
an electron to become stable. Accepting an
electron gives halogens a -1 charge.
Practice
 What is the oxidation state of Oxide?
 What is the oxidation state of Iodide?
 What is the oxidation state of a Calcium ion?
 What is the oxidation state of a Lithium ion?
Answers
 -2
 -1
 +2
 +1
Net Ionic Equation
 To create a net ionic equation, you break apart all
ionic molecules in a balanced molecular equation
into their ions if they are soluble.
 Do not break up gases or solids !!!
 Solids, pure liquids and gases have no charges.
 If there are spectator ions, ions that appear on both
sides of the equation, they cancel each other.
Net Ionic Example
 Silver nitrate is mixed with potassium chromate
Molecular Equation
2AgNO3 + K2CrO4 → Ag2CrO4 + 2KNO3
Complete ionic equation
2Ag+ + 2NO3ˉ + 2K+ + CrO4-2 → Ag2CrO4 + 2K+ + 2NO3-2
Net Ionic Equation
2Ag+ + CrO4-2 → Ag2CrO4
Solubility Rules
 NO3-
all nitrates are soluble
 CH3COO- or C2H3O2all acetates are soluble except AgCH3COO-1
 ClO3- all chlorates are soluble
 Cl- all chlorides are soluble except AgCl, Hg Cl , PbCl
2
 Br-
2
2
all bromides are soluble except AgBr, PbBr2, Hg2Br2, and
HgBr2
 I-
all iodides are soluble except AgI, Hg2I2, HgI, and PbI2
Solubility Rules, contd.
 SO4 -2
all sulfates are soluble except BaSO4, PbSO4,
Hg2SO4, CaSO4, AgSO4 and SrSO4
 Alkali metal cations, and NH4+1 are all soluble
 H+
all common inorganic acids and low molecular mass
organic acids are soluble
(In)Solubility Rules, contd.
-
 CO3 ²
all carbonates are insoluble except those of alkali
metals and NH4
-
 CrO4 ²
all chromates are insoluble except those of alkali
metals, NH4, CaCrO4, and SrCO4
-
 OH
all hydroxides are insoluble except those of the
alkali metals, NH4, Ba(OH)2, Sr(OH)2, and Ca(OH)2
-
 PO4 ³
all phosphates are insoluble except those of alkali
metals and NH4
-
 SO3 ²
all sulfites are insoluble except those of alkali
metals and NH4
-
 S²
all sulfides are insoluble except those of alkali
metals and NH4
Strong Acids
HCl
HNO3
HBr
H2SO4
HI
HClO4
Strong Bases
 Generally, strong bases are made up of a metal ion and
a hydroxide ion.
LiOH
Ca(OH)2
NaOH
Sr(OH)2
KOH
Ba(OH)2
Strong Acids and Bases
 Strong acids dissociate completely in water, so
the reaction goes to completion and they never
reach equilibrium with their conjugate bases.
 Because there is no equilibrium, there is no
equilibrium constant, so there is no dissociation
constant for strong acids and bases.
Salts
 Salts are generally formed from a
cation (on the far left side of the periodic table) and
an anion (on the far right side of the table)
 Salts that are soluble in water include all of the salts of:
Cations
lithium
sodium
potassium
ammonium
Anions
nitrate
acetate
Check the solubility rules for other soluble/insoluble salts
Diatomic Molecules
 You can use a mnemonic device to help you remember
the diatomic molecules:
 BrINClHOF (say “Brinkelhof”)
 Help Our Needy Class Find Brains Immediately
Synthesis
 Synthesis occurs when two or more reactants
combine to form a single product.

 There are several common types of
synthesis reaction.
Synthesis Examples
metal combines with a nonmetal to form a binary
salt.
A piece of lithium metal is dropped into a container of
nitrogen gas.
6Li+ N2  2Li3N
Metal oxide and water forms a base
(metallic hydroxide)
Solid sodium oxide is added to water.
Na2O + H2O 2NaOH
Synthesis, contd.
 Nonmetal oxide and water forms acids.
Nonmetal retains its oxidation number.
-Carbon dioxide is burned in water.
CO2 + H2O  H2CO3
 Metallic oxide and nonmetallic oxide form salt.
-Solid sodium oxide is added to carbon dioxide.
CaO + SO2  CaSO3
Decomposition
 Occurs when a single reactant is broken down into two
or more products.
 The reactants react to form basic compounds or
elements.
 When a compound is heated or electrolyzed, it means
that it is broken up into its ions.
 AB A+B
Decomposition Example
Base  metal oxide + water
Ca(OH)2  CaO + HOH
Acid containing oxygen  non metal oxide + water
H2CO3  CO2 + HOH
Salt containing oxygen  metal oxide + nonmetal oxide
CaCO3  CaO + CO2
Examples of Decomposition
 A sample of magnesium carbonate is heated.
MgCO3 
MgO + CO2
 Molten sodium chloride is electrolyzed.
2NaCl  2Na + Cl2
 A sample of ammonium carbonate is heated.
(NH4)2CO3 
2NH3 + H2O + CO2
Single Replacement
 Reactions that involve an element replacing one part of
a compound. The products include the displace
element and a new compound. An element can only
replace another element that is less active than itself.
(Look a activity series/ AP packet)
 Generally, synthesis reactions occur when the two
reactants come from the following types of compounds:
acid, base, salt, water
 A +BX B+AX
Single Replacement
Active metals replace less active metals from the less
active metals’ compounds in aqueous solutions
3Mg+ 2FeCl3 —> 2Fe + 3MgCl2
Active metals replace hydrogen in water
2Na + 2H2O —> H2 + 2NaOH
Active metals replace hydrogen in acids
2Li + 2HCl —> H2 + 2LiCl
Single Replacement Rules, contd.
Active nonmetals replace less active nonmetals from
their compounds in aqueous solutions
Cl2 + 2KI —> I2 + 2KCl
If a less reactive element is combined with a more
reactive element in compound form, there will be no
reaction
Cl2 + KF —> no reaction*
* On the AP test reactions will ALWAYS have products; it
will never be “no reaction.”
Activity Series (Single Replacement)
 Metals
Li, Ca, Na, Mg, Al, Zn, Fe, Pb, [H2], Cu, Ag, Pt
 Nonmetals
F2, Cl2, Br2, I2,
More active

Less Active
Double Replacement
 Two compounds react to form two new compounds. No
changes in oxidation numbers occur.
 Each cation pairs up with the anion in the other compound.
 The “driving force” in these reactions is the removal of at
least one pair of ions from solution.
 This removal of ions happens with the formation of a
precipitate, gas, or molecular species.
 When a double replacement reaction doesn’t go to
completion, it is a reversible reaction (no ions have been
removed).
 AX+ BY  AY+ BX
How do you know a double
replacement reaction occurs?
 One of the products will be a(n):
gas
insoluble precipitate
molecular species
*Remember– on the AP test the reaction will always occur
Examples of Dbl. Replacement
 Solutions of potassium bromide and silver nitrate are
mixed.
KBr + AgNO3  AgBr + KNO3
 A solution of sodium sulfate is added to a solution of
hydrochloric acid.
Na2SO3 + 2HCl  2NaCl + H2SO3
Remember that one of your products must be a solid or a gas.
Common Gases Released
(Dbl. Repl.)
 H2S Any sulfide plus any acid forms H2S and a salt.
 CO2 Any carbonate plus any acid form CO3, water, and
a salt.
 SO2 Any sulfite plus any acid form SO2, water, and a
salt.
 NH3 Any ammonium plus a soluble hydroxide form
NH3, water, and a salt.
Solubility Computer Tasks
 Task #1
 Go to the site listed below which is a tutorial on
precipitation reactions. Follow all directions.
 Record the complete molecular reaction for each
combination of solutions you mix. Identify the
precipitate (name and formula) produced.
 http: www.wisconline.com/objects/index_tj.asp?objID=GCH2904
Solubility Computer Tasks
 Task # 2
 Go to the site below and mix two solutions at a time.
 Write the complete molecular equations for each
combination of solutions.
 Identify the precipitate (name and formula) that is produced.
(You should have three reactions when you are finished.)

 http://
www.mhhe.com/physsci/chemistry/animations/chang_7e_es
p/crm3s2_3.swf
Acid/ Base Reactions
(Dbl. Repl.)
 An acid and a base will react and form water and a salt.
 Hydrochloric acid is added to sodium hydroxide.
HCl + NaOH  NaCl + H2O
Acid/Base Reactions
 This is a neutralization reaction.
 Remember:
 Weak acids & bases do not dissociate in water
 Strong acids & bases do dissociate in water
Hydrolysis (Dbl. Repl.)
 It is the reverse of neutralization and results when a salt plus
a water molecule yields an acid plus a base.
 Salt + water  acid + base
 Key things to know about hydrolysis reactions:
 Salts of a strong acid plus a weak base will hydrolyze into
an acidic solution.
 NH4+ +Cl- +H2O →
H+ +Cl- + (NH)4OH
 Salts of a weak acid and a strong base will always
hydrolyze to give a basic solution.
 K+ +F- +H2O → K+ +OH- +HF
Hydrolysis
 Salts of a strong acid and a strong base will never
undergo hydrolysis and therefore make a neutral solution.
Na+ + Cl-1 + H2O → Na+1 + OH-1 + H+1 + Cl-1

 Salts of a weak acid plus salts of a weak base may
hydrolyze as an acid, base, or a neutral solution; the final
result depends on the Ka’s and Kb’s of the acids and
bases formed during the hydrolysis process.
 Disclaimer!! The spectator ions were not removed 
Hydrolysis Sample Problems
 Try these:
 An aqueous solution of manganese (II) sulfate undergoes
hydrolysis.
 Ammonium fluoride and water are mixed together.
 Answers are on the next slide.
Hydrolysis answers
 MnSO4 + 2H2O → H2SO4 + Mn(OH)2
 NH4F + H2O → HF + NH4OH
Gas Producing Reactions
Acid + Metal carbonate → Salt + Water + Carbon dioxide
H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)
Combustion (Organic Rxns.)
 An organic compound reacts with O2 and an ignition
source to form water and carbon dioxide.
 If something is burned there is a combustion reaction.
 Methanol is burned in oxygen gas.
2CH3OH + 3O2  4H2O + 2CO2
Combustion
 On the AP exam:
 If the reaction is a combustion reaction and you don’t
know the chemical formula for the hydrocarbon, make
up a chemical formula and complete the reaction. You
will earn partial points.
Addition (Organic Rxns)
 A halogen, or hydrogen, is added to an alkene or
alkyne, breaking apart the double or triple bonds and
forming one compound with single bonds.
 This is an addition to multiple bonds.
 Fluorine is added to ethene
F2 + CH2=CH2  CH2F-CH2F
Substitution (Organic Rxns.)
 An atom attached to a carbon is removed and
something else takes its place. Classic reaction for
organic cpds with no multiple bonds.
 This is a substitution of single bonds.
 Bromine is added to methane
Br2 + CH4  CH3Br + HBr
Esterification
(ether formation)
 An organic acid reacts with an alcohol to form an ester and
water.
organic acid + alcohol  ester + water
CH3CH2COOH + CH3CH2CH2CH2OH 
CH3CH2COOCH2CH2CH2CH3 + H20
Ether Formation
alcohol + alcohol  ether + water
C2H5OH + C2H5OH  C2H5OC2H5 + H2O
Oxidizing Agents
(Redox Rxns.)
Common Oxidizing Agents
MnO4¯ in acidic solution

MnO2 in acidic solution

MnO4¯ in neutral or basic solution

Cr2O7ˉ² in acidic solution

HNO3, concentrated

HNO3, dilute

H2SO4, hot, concentrated

Metallic ions (higher oxidation #)

Free halogens

Na2O2

HClO4

C2O4ˉ²

H 2O2
Products Formed
Mn +²
Mn +²
MnO2(s)
Cr +³
NO2
NO
SO2
Metallous ions (lower oxidation #)
Halide ions
NaOH
Clˉ
CO2
O2
Handy Hint
 If the reaction prediction shows a chemical formula,
such as, manganese (IV) oxide as a reactant, the
reaction is probably an oxidation/reduction reaction.
Reduction Agents
(Redox Rxns)
Common Reducing Agents

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
Halide ions
Free metals
Sulfite ions or SO2
Nitrite ions
Free halogens, dilute basic
solution
 Free halogens,
concentrated basic solution
 Metallous ions (lower
oxidation #)
Products Formed
Free halogen
Metal ions
Sulfate ions
Nitrate ions
Hypohalite ions
Halite ions
Metallic ions
(higher oxidation #)
Electrolysis (Redox Rxns)
 An electrolysis reaction is a reaction in which a
non-spontaneous redox reaction is brought about
by the passage of current under sufficient external
electrical potential. The devices in which
electrolysis reactions occur are called electrolytic
cells.
 In theory, E° values (Standard Reduction
Potentials) can be used to predict which element
will plate out at a particular electrode when various
solutions are combined.
 (B&L text)
Rules for Predicting Cathode
Reactions (Reduction)
 When a direct electric current is passed through a water
solution of an electrolyte, two possible reduction
processes may occur at the cathode.
 The cation may be reduced to the corresponding metal.
Mn+ + ne-  M(s) (reaction 1)
n = (charge of cation)
 Water molecule may be reduced to elementary hydrogen
2H2O + 2eˉ  H2 + 2OHˉ (reaction 2)
Rules for Predicting Cathode
Reactions, contd.
 For salts containing transition metal cations, which
are relatively easy to reduced compared to water,
reaction #1 will occur at the cathode (and the
transition metal will plate out).
Mn+ + ne-  M(s)
 If the cation is representative metal, the water
molecules will be easier to reduce compared to the
cation, and reaction #2 will occur at the cathode,
producing hydrogen gas and hydrogen ions.
2H2O + 2eˉ  H2 + 2OHˉ
Rules for Predicting Anode
Reaction (oxidation)
 The oxidation process that occurs at the anode of an
electrolytic cell operating in aqueous solution may be
one of two oxidation processes.
 The anion may be oxidized to the corresponding
nonmetal.
- 2Xˉ  X2 + 2eˉ (reaction 1)
 Water molecules may be oxidized to elementary
oxygen.
- HOH  ½ O2 + 2H+ + 2eˉ (reaction 2)
Rules for Predicting Anode
Reactions, contd.
 For salts containing iodide, bromide, or chloride ions, it
is usually easier to oxidize these nonmetals rather than
water. It will be found that the nonmetal is formed at the
anode.
 When the anion present is any other ion that is more
difficult to oxidize than water, Reaction #2 will occur at
the anode producing elementary oxygen and aqueous
hydrogen ions.
Example Electrolysis
Reactions
1. Copper (II) chloride in water
Cu+2 + 2Clˉ  Cu + Cl2
2. Copper (II) sulfate in water
Cu+2 + HOH  Cu + ½ O2 + 2H+
3. Sodium chloride in water
2Clˉ + 2HOH  H2 + Cl2 + 2OHˉ
4. Sodium sulfate in water
2HOH  2H2 + O2
Metals w/ Multiple Oxidation
Levels (Redox Rxns)

These metals can change their oxidation state in a redox reaction
 Antimony (III) or (V)
 Bismuth (III) or (IV)
 Cerium (III) or (IV)
 Chromium (II) or (III)
 Cobalt (II) or (III)
 Copper (I) or (II)
 Gallium (I) or (II) or (III)
 Germanium (II) or (IV)
 Gold (I) or (III)
 Iron (II) or (III)
 Lead (II) or (IV)
 Mercury (I) or (II)
 Nickel (II) or (III)
 Thallium (I) or (III)
 Thorium (II) or (IV)
 Tin (II) or (IV)

Tin (II) sulfate is added to iron (III) sulfate
SnSO4 + Fe2(SO4)3  Sn(SO4)2 + 2FeSO4
Complex Ion Reactions
 Nomenclature is on pages 23-27 of The
Ultimate Chemical Equations Handbook
 There are a lot of very complicated types of
these reactions, but, for all intensive purposes
and for the AP test, you only need to be familiar
with those reactions pertaining to ammonia and
water.
 In a complex ion reaction, ligands will attach to
a transition metal ion.
 There will usually be twice as many ligands as
the metal’s oxidation number
Complex Ion Reactions,
contd.
 These reactions usually occur in a
concentrated solution of the ligand.
 Copper chloride (II) is added to a
concentrated solution of ammonia
 Cu2+ +NH3  [Cu(NH3)4]2+
Common Reaction Terms
 Electrolysis: Electricity is run through a compound,
resulting in a change of oxidation states.
 Hydrolysis: The reaction of a salt with water to form
molecular species. Salts of a strong acid + a weak base
will always hydrolyze to give an acidic solution.
 Neutralization: Acid and base react to form a salt and
water.
 Catalyst: A molecule that speeds that speeds a reaction
but that does not appear in the reaction.
 Oxidation number: the charge that it would have if all
the ligands (atoms that donate electrons) were removed
along with the electron pairs that were shared with the
central atom
Common Reaction Terms,
contd.
 Precipitate: an insoluble substance formed by the
reaction of two aqueous substances.
 Anode: the electrode where oxidation occurs
an ox
 Cathode: the electrode where reduction occurs
red cat
 By: Will Lambert, Adam Robinson, Michelle Klassen,
and Tori Waldron
 (AP Chem ‘06-’07)