Reaction PredictionsRev. 01/23/12

ObjectivesSWBAT

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 FormatYou 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 WayAlways 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

Hydrogen H+

Sodium Na+

Potassium K+

Calcium Ca+²Magnesium Mg+²Iron (Ferrous) Fe+²Iron (Ferric) Fe+³

•Hydroxide OHˉ•Chloride Clˉ•Sulfide Sˉ²•Bicarbonate HCOзˉ•Carbonate COзˉ²•Sulfate SO4ˉ²•Phosphate PO4ˉ ³

TipGroup 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.

PracticeWhat 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 EquationTo 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 ExampleSilver nitrate is mixed with potassium

chromate

Molecular Equation2AgNO3 + K2CrO4 → Ag2CrO4 + 2KNO3

Complete ionic equation

2Ag+ + 2NO3ˉ + 2K+ + CrO4-2 → Ag2CrO4 + 2K+ + 2NO3-2

Net Ionic Equation

2Ag+ + CrO4-2 → Ag2CrO4

Solubility RulesNO3

- all nitrates are soluble

CH3COO- or C2H3O2-

all acetates are soluble except AgCH3COO-1

ClO3- all chlorates are soluble

Cl- all chlorides are soluble except AgCl, Hg2Cl2, PbCl2

Br- 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

S-² all sulfides are insoluble except those of alkali metals and NH4

Strong AcidsHCl HNO3

HBr H2SO4

HI HClO4

Strong BasesGenerally, 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 BasesStrong 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.

SaltsSalts 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 Anionslithium nitratesodium acetatepotassiumammonium

Check the solubility rules for other soluble/insoluble salts

Diatomic MoleculesYou can use a mnemonic device to help you

remember the diatomic molecules:

BrINClHOF (say “Brinkelhof”)

Help Our Needy Class Find Brains Immediately

SynthesisSynthesis occurs when two or more reactants

combine to form a single product.

There are several common types of synthesis reaction.

 

Synthesis Examplesmetal 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

DecompositionOccurs 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 ExampleBase 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 ReplacementReactions 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 water2Na + 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 solutionsCl2 + 2KI —> I2 + 2KCl

If a less reactive element is combined with a more reactive element in compound form, there will be no reactionCl2 + KF —> no reaction*

* On the AP test reactions will ALWAYS have products; it will never be “no reaction.”

Activity Series (Single Replacement)

MetalsLi, Ca, Na, Mg, Al, Zn, Fe, Pb, [H2], Cu, Ag, Pt 

NonmetalsF2, Cl2, Br2, I2,

More active Less Active

Double ReplacementTwo 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 TasksTask #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.wisc-online.com/objects/index_tj.asp?objID=GCH2904

Solubility Computer TasksTask # 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_esp/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 ReactionsThis is a neutralization reaction.

Remember:Weak acids & bases do not dissociate in waterStrong 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 ProblemsTry these:

An aqueous solution of manganese (II) sulfate undergoes hydrolysis.

Ammonium fluoride and water are mixed together.

Answers are on the next slide.

Hydrolysis answersMnSO4 + 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

CombustionOn 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 FormedMn +²Mn +²MnO2(s)Cr +³NO2

NOSO2

Metallous ions (lower oxidation #)Halide ionsNaOHClˉCO2

O2

Handy HintIf 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 AgentsHalide ionsFree metalsSulfite ions or SO2

Nitrite ionsFree halogens, dilute

basic solutionFree halogens,

concentrated basic solution

Metallous ions (lower oxidation #)

Products FormedFree halogenMetal ionsSulfate ionsNitrate ionsHypohalite ionsHalite ionsMetallic 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) sulfateSnSO4 + Fe2(SO4)3 Sn(SO4)2 + 2FeSO4

Complex Ion ReactionsNomenclature is on pages 23-27 of The

Ultimate Chemical Equations HandbookThere 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 ammoniaCu2+ +NH3 [Cu(NH3)4]2+

Common Reaction TermsElectrolysis: 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 occursan ox

Cathode: the electrode where reduction occursred cat

By: Will Lambert, Adam Robinson, Michelle Klassen, and Tori Waldron

(AP Chem ‘06-’07)