Reaction Predictions

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Reaction Predictions
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Most Commonly Used Cations and Anions

• Hydroxide OH
• Chloride Cl
• Sulfide S²
• Bicarbonate HCO?
• Carbonate CO?²
• Sulfate SO4²
• Phosphate PO4³

• Hydrogen H
• Sodium Na
• Potassium K
• Calcium Ca²
• Magnesium Mg²
• Iron (Ferrous) Fe²
• Iron (Ferric) Fe³

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Cations/ Anions, contd.

• You can figure out the charge of an ion by using
  the periodic table. For Example
• 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.

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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?

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Answers

• -2
• -1
• 2
• 1

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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.
• If there are spectator ions, ions that appear on
  both sides of the equation, they cancel each
  other.

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Net Ionic Example

• Silver nitrate is mixed with potassium chromate
• 2AgNO3 K2CrO4 ? Ag2CrO4 2KNO3 Molecular
  Equation
• 2Ag 2NO3 2K CrO4-2 ? Ag2CrO4 2K
  2NO3-2 Complete ionic equation
• 2Ag CrO4-2 ? Ag2CrO4 Net Ionic Equation

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Solubility Rules

• NO3- all nitrates are soluble
• CH3COO- or C2H3O2-
• all acetates are soluble except AgCH3COO
• 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

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Solubility Rules, contd.

• SO4² all sulfates are soluble except BaSO4,
  PbSO4, Hg2SO4, CaSO4, AgSO4 and SrSO4
• Alkali metal, cations, and NH4 all are soluble
• H all common inorganic acids and low
  molecular mass organic acids are soluble

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(In)Soubility 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

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Synthesis

• Synthesis occurs when two or more reactants
  combine to form a single product. There are
  several common types of synthesis reaction.
•  
• You know it happens when you have
• -A metal combines with a nonmetal to form a
  bianary 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

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Synthesis, contd.

• Nonmetal oxide and water forms acids. Nonmetal
  retains its oxidation number.
•   -Carbon dioxide is burned in water.
• CO2 H2O ?  H2CO3
• Metallic oxides and nonmetallic oxides form
  salts.
•   -Solid sodium oxide is added to carbon
  dioxide.
• Na2O CO2 ? Na2CO2

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Decomposition

• Occurs when a single reactant is broken down into
  two or more products.
• The reactions 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 ?AB

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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

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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)
• A BX ?BAX

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Single Replacement Rules

• Active metals replace less active metals from the
  less active metals compounds in aqueous
  solutionsex. 3Mg 2FeCl3gt 2Fe 3MgCl2
• Active metals replace hydrogen in waterex. 2Na
  2H2Ogt H2 2NaOH
• Active metals replace hydrogen in acids ex. 2Li
  2HCl gt H2 2LiCl

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Single Replacement Rules, contd.

• 4. Active nonmetals replace less active nonmetals
  from their compounds in aqueous solutionsex. Cl2
  2KI gt I2 2KCl
• 5. If a less reactive element is combined with a
  more reactive element in compound form, there
  will be no reactionex. Cl2 KF gt no reaction
• On the AP test reactions will ALWAYS have
  products it will never be no reaction.

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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

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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 doesnt go to
  completion, it is a reversible reaction (no ions
  have been removed).
• AX BY ? AY BX

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How do you know a double replacement reaction
occurs?

• The reactants will contain a(n)
• -gas
• -insoluble precipitate
• -molecular species
• Remember on the AP test the reaction will
  always occur

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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.

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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

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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 
• Salts of a strong acid and a strong base will
  never undergo hydrolysis and therefore make a
  neutral solution.
• Na   Cl-  H2O   ?   Na   OH-   H   Cl- 
• 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 Kas
  and Kbs of the acids and bases formed during the
  hydrolysis process.
• Disclaimer!! The spectator ions were not removed ?

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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

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Hydrolysis Sample Problems

• Try these
• An aqueous solution of manganese (II) sulfate
  undergoes hydrolysis.
• Ammonium fluoride and water are mixed together.

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Hydrolysis answers

• MnSO4 2H2O ?  H2SO4 Mn(OH)2
• NH4F H2O ? HF NH4OH

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Combustion (Organic Reacs.)

• An organic compound reacts with O2 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

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Addition (Organic Reacs.)

• A halogen or hydrogen is added to an alkene or
  alkyne, breaking apart the double or triple bonds
  and forming single bonds.
• Fluorine is added to ethene F2 CH2CH2 ?
  CH2F-CH2F

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Substitution (Organic Reacs.)

• An atom attached to a carbon is removed and
  something else takes its place.
• Bromine is added to methane Br2 CH4 ? CH3Br
  HBr

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Oxidizing Agents (Redox Reacs.)

• Common Oxidizing Agents
• MnO4 in acidic solution
• MnO2 in acidic solution
• MnO4 in neutral or basic solution
• Cr2O7² in acidic solution
• HNO3, concentrated
• HNO3, dilute
• H2SO4, hot, concentrated
• Metallic ions (higher oxidation )
• Free halogens
• Na2O2
• HClO4
• C2O4²
• H 2O2

Products Formed Mn² Mn² MnO2(s) Cr³ NO2 NO SO2
Metallous ions (lower oxidation ) Halide
ions NaOH Cl CO2 O2
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Reduction Agents (Redo Reacs.)

• Common Reducing Agents
• 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 )
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Electrolysis (Redox Reacs.)

• 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.
• (BL text)

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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 2e ? H2 2OH (reaction 2)

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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 2e ? H2 2OH

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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.
• - 2X ? X2 2e (reaction 1)
• Water molecules may be oxidized to elementary
  oxygen.
• - HOH ? ½ O2 2H 2e (reaction 2)

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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.

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Example Electrolysis Reactions

• Copper (II) chloride in water
• Cu2 2Cl ? Cu Cl2
• 2. Copper (II) sulfate in water
• Cu2 HOH ? Cu ½ O2 2H
• 3. Sodium chloride in water
• 2Cl 2HOH ? H2 Cl2 2OH
• 4. Sodium sulfate in water 2HOH ? 2H2 O2

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Metals w/ Multiple Oxidation Levels (Redox Reacs.)

• 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

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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 metals oxidation number

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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)42

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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

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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

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• By Will Lambert, Adam Robinson, Michelle
  Klassen, and Tori Waldron
• (APChem 06-07)