Predicting Reaction Products - Question 4

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Predicting Reaction Products - Question 4

• David Lee
• Retired AP Chemistry Teacher
• 35 years at Mountain Lakes HS

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Predicting Reaction Products - Question 4

• All workshop participants will receive a CD
  containing this PowerPoint slide presentation as
  well as the three papers Predicting Reaction
  Products, AP Chem Exam - Question 4, and AP
  Chem Exam - Question 4 Answers.

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Predicting Reaction Products - Question 4

• This PowerPoint slide presentation may be used as
  a classroom introduction to solving Question 4
  reactions. You may modify it to meet the needs
  of your students.

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Agenda

• Why are we here?
• Classification of reactions
• Sample reactions
• How to get the highest possible score
• A short quiz (wont be scored)
• Q A

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Why Are We Here?

• Question 4 is found on EVERY AP Chemistry Exam
• 15 of total exam grade
• Students have poor results
• Textbooks do not have a chapter devoted to this
  topic.

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Poor Student Scores

• In 2002 the average score was 5.5 out of a
  possible 15 points.
• Generally the LOWEST score of the Free
  Response Section

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Free Response Section of the AP Chemistry Exam

• Choice of 8 reactions
• Answer 5 to get full credit
• 1 point for correct reactants
• 2 points for correct products
• 3 points each for a total of 15 points.
• Physical states balancing are not necessary

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Successfully Predicting Reaction Products

• Know the list of Common Ions
• Knowledge of Nomenclature
• Learn the Solubility Rules
• Know the Reaction Classifications
• Write net ionic equations

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Classification of Reactions

• Acid/Base
• Precipitation
• Hydrolysis
• Decomposition ( reversed)
• Ligands
• REDOX
• Organic

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Acid/Base Reactions

• HX MOH ----gt MX HOH
• Weak acids weak bases must be written as
  molecules
• Strong acids strong bases must be written as
  ions.

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Acid/Base Reactions

• Soluble salts (MX) are completely ionized in
  water.
• Remove spectator ions write the net ionic
  equation.

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Acid/Base Reaction Sample 1

• 1991 (c) equal volumes of 0.1-molar sulfuric
  acid and 0.1-molar potassium hydroxide are mixed.
• H2SO4 is a strong acid
• KOH is a strong base
• Both are written as ions in water
• H2SO4 KOH ----gt (1 point scored for correct
  reactants)

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Acid/Base Reaction Sample 1

• H2SO4 KOH ---gt K2SO4 HOH (scores 2 points
  total since it is NOT written as a net ionic
  equation)
• H OH- ----gt HOH (scores all 3 points
  since it is a net ionic equation)

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Acid/Base Sample 2

• 1998 (d) Equal volumes of equimolar solutions
  of phosphoric acid and potassium hydroxide are
  mixed.
• Phosphoric acid is a weak acid.
• Potassium hydroxide is a strong base.

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Acid/Base Sample 2

• H3PO4 KOH ----gt (1 point)
• H3PO4 KOH ----gt KH2PO4 HOH (2
  points - NOT net ionic)

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Acid/Base Sample 2

• H3PO4 OH- ----gt H2PO4- HOH (3 points)
• H3PO4 OH- ----gt PO43- HOH (2 points -
  does NOT show equimole relationship)

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Precipitation Reactions

• One or more products is(are) not significantly
  soluble in water.
• Generally both reactants are salts in solution

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Precipitation Reactions

• General equation
  AX BY -----gt AY BX Where AY
  and/or BX is(are) insoluble in water

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Precipitation Reactions

• Net ionic equation
• A Y- -----gt AY
• where AY is insoluble in water BX is soluble
  in water

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Precipitation Reactions Sample 1

• 2003B (d) A solution of lead(II) nitrate is
  added to a solution of potassium sulfate.
• Pb(NO3)2 K2SO4 -----gt (scores 1
  point for correct reactants)

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Precipitation Reactions Sample 1

• Pb(NO3)2 K2SO4 -----gt PbSO4
  KNO3(scores 2 points for correct answer but not
  in net ionic form)
• Pb2 SO42- -----gt PbSO4 (scores 3 points
  for correct net ionic answer)

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Precipitation Reactions Sample 2

• 2002 (a) A solution of sodium iodide is added
  to a solution of lead(II) acetate.
• NaI Pb(C2H3O2)2 ----gt (1 point)
• NaI Pb(C2H3O2)2 ----gt PbI2 Na C2H3O2
  (2 points since it is NOT net ionic)

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Precipitation Reactions Sample 2

• I- Pb2 ----gt PbI2 (3 points
  for net ionic equation)

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Hydrolysis Reactions

• Generally three types
• A metal oxide reacts with water to form a base.
• A nonmetal oxide reacts with water to form an
  acid.
• A metal hydride reacts with water to form a base
  hydrogen gas.

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Hydrolysis Reaction Sample 1

• A metal oxide reacts with water to form a
  base.
• 2002 (c) Solid cesium oxide is added to water.
• Cs2O H2O -----gt (1 point)
• Cs2O H2O -----gt CsOH (2 points)
• Cs2O H2O -----gt Cs OH- (3
  points)

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Hydrolysis Reaction Sample 2

• A nonmetal oxide reacts with water to form an
  acid.
• 2003 (h) solid dinitrogen pentoxide is added
  to water.
• N2O5 H2O -----gt (1 point)
• N2O5 H2O -----gt HNO3 (2 points)
• N2O5 H2O -----gt H NO3-
  (3 points)

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Hydrolysis Reaction Sample 3

• A metal hydride reacts with water to form a
  base hydrogen gas.
• 1995 (g) Solid calcium hydride is added to
  distilled water.
• CaH2 H2O -----gt (1 point)
• CaH2 H2O -----gt Ca(OH)2 H2 (2
  points)

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Hydrolysis Reaction Sample 3

• CaH2 H2O -----gt Ca2 OH - H2
  (3 points)

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Decomposition Reactions

• A lone compound is strongly heated, exposed to
  strong sunlight or electric current.

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Decomposition Reactions

• Compounds that readily decompose
• Metallic carbonates
• Most metallic hydroxides
• Metallic chlorates
• Metallic sulfites
• Some acids
• Peroxides
• Electrolysis of salts

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Decomposition Reaction Sample 1

• Metallic carbonates decompose to form a
  metallic oxide carbon dioxide.
• 1996 (a) Solid calcium carbonate is strongly
  heated.
• CaCO3 -----gt (1 point)
• CaCO3 -----gt CaO CO2 (3 points)

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Decomposition Reaction Sample 2

• Most metallic hydroxides, when strongly
  heated, form metal oxides and water.
• Solid calcium hydroxide is strongly heated.
• Ca(OH)2 -----gt (1 point)
• Ca(OH)2 -----gt CaO H2O (3 points)

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Decomposition Reaction Sample 3

• Metallic chlorates, when strongly heated, form
  metallic chlorides and oxygen gas.
• Solid potassium chlorate is strongly heated.
• KClO3 -----gt (1 point)
• KClO3 -----gt KCl O2 (3 points)

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Decomposition Reaction Sample 4

• Metallic sulfites, when strongly heated form
  metallic oxides and sulfur dioxide gas.
• 1998 (e) Solid calcium sulfite is heated in
  a vacuum.
• CaSO3 -----gt (1 point)
• CaSO3 -----gt CaO SO2 (3 points)

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Decomposition Reaction Sample 5

• Some acids decompose into nonmetallic oxides
  water.
• Carbonic acid readily decomposes in water
  solution to form carbon dioxide and water.
• H2CO3 -----gt (1 point)
• H2CO3 -----gt CO2 H2O (3 points)

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Decomposition Reaction Sample 6

• Sulfurous acid readily decomposes in water
  solution to form sulfur dioxide and water.
• H2SO3 -----gt (1 point)
• H2SO3 -----gt SO2 H2O (3 points)

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Decomposition Reaction Sample 7

• Hydrogen peroxide decompose into water and
  oxygen gas.
• H2O2 -----gt (1 point)
• H2O2 -----gt H2O O2 (3 points)

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Decomposition Reaction Sample 8

• Electrolysis of molten salts produces elements
  from the ions.
• Molten magnesium bromide is electrolyzed using
  inert electrodes.
• MgBr2 -----gt (1 point)
• MgBr2 -----gt Mg Br2 (3 points)
• Since water is not present MgBr2 is not
  written as separate ions.

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Ligand Reactions

• Ligand reactions involve the reaction between
  ligands and some metal anions (Fe, Cu, Pb, Ag,
  Au, Sn, Pt, Co, etc).
• Learn the common ligands CN-, SCN-, NO2- ,
  NH3, H2O, OH-, halides (F-, Cl-, Br-, I-)

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Ligand Reactions

• General rule The number of ligands attached
  to the metallic anion is usually DOUBLE the
  anions charge.
• Ag(NH3)2 Cu(NH3)42 Fe(NH3)63 Ag
  Cu2 Fe3

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Ligand Reactions Sample 1

• 2003 (e) Excess concentrated aqueous ammonia
  is added to solid silver chloride.
• NH3 AgCl -----gt (1 point)
• NH3 AgCl -----gt Ag(NH3)2 Cl-
  (3 points)

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Ligand Reactions Sample 2

• 1989 (f) A solution of ammonium thiocyanate
  is added to a solution of iron(III) chloride.
• NH4SCN FeCl3 -----gt (1 point)
• NH4SCN FeCl3 -----gt
• (NH4)3 Fe(SCN)6 NH4Cl
  (2 points)

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Ligand Reactions Sample 2

• SCN- Fe3 -----gt Fe(SCN)63-
• (3 points)

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REDOX Reactions

• REDOX reactions make up about 33 of the Question
  4. Thats about 2 out of the 8 reactions!!!
• These are reactions that involve CHANGES in
  oxidation state.
• Learn the list of important oxidizers and
  reducers from pages 7 9 of Predicting Reaction
  Products.

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REDOX ReactionsSample 1

• Sample Composition reactions where metal
  nonmetal elements react to form a compound.
• 2003 (f) Magnesium ribbon is burned in
  oxygen.
• Mg O2 -----gt (1 point)
• Mg O2 -----gt MgO (3 points)

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REDOX ReactionsSample 2

• Sample Single replacement reactions where a
  metal replaces the metal anion from a metallic
  compound.
• 2003 (g) A bar of strontium metal is immersed
  in a 0.1 M copper(II) nitrate solution.
• Sr Cu(NO3)2 -----gt (1 point)

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REDOX ReactionsSample 2

• Sr Cu(NO3)2 -----gt Sr(NO3)2 Cu (2
  points)
• Sr Cu2 -----gt Sr2 Cu (3 points)

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REDOX ReactionsSample 3

• Sample Single replacement reactions where
  halogen replaces the halide from a halide salt.

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REDOX ReactionsSample 3

• 2001 (f) Chlorine gas is bubbled through a
  solution of potassium bromide.
• Cl2 KBr -----gt (1 point)
• Cl2 KBr -----gt KCl Br2 (2
  points)
• Cl2 Br- -----gt Cl- Br2 (3
  points)

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REDOX ReactionsSample 4

• 2002 (g) Acidified solutions of potassium
  permanganate and iron(II) nitrate are mixed
  together.
• H KMnO4 Fe(NO3)2 -----gt (1
  point)
• H KMnO4 Fe(NO3)2 -----gt Fe (NO3)3
  Mn (NO3)2 H2O (2 points)

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REDOX ReactionsSample 4

• H MnO4- Fe2 -----gt Fe3
  Mn2 H2O (3 points)

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REDOX ReactionsSample 5

• 2001 (e) A solution of iron(II) chloride is
  added to an acidified solution of sodium
  dichromate.
• FeCl2 H Na2Cr2O7 -----gt (1
  point)
• FeCl2 H Na2Cr2O7 -----gt FeCl3
  CrCl3 NaCl H2O (2 points)

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REDOX ReactionsSample 5

• Fe2 H Cr2O72- -----gt Fe3
  Cr3 H2O (3 points)

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REDOX ReactionsSample 6

• 1993 (a) A strip of copper is immersed in
  dilute nitric acid
• Cu HNO3 ----gt (1 point)
• Cu HNO3 ----gt Cu(NO3)2 NO
  H2O (2 points)
• Cu H NO3- ----gt Cu2 NO H2O
  (3 points)

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Organic Reactions

• Reactions involving compounds containing
  hydrogen, carbon, and sometimes other nonmetal
  elements.
• Learn the hydrocarbon nomenclature and common
  functional groups. (page 10 of Predicting
  Reaction Products)
• About 1 organic question per exam.

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Organic ReactionsSample 1

• Combustion of organic compounds.
• Burning in air (oxygen) produces carbon dioxide,
  water, and nonmetal oxides of the other nonmetal
  elements.
• 2003B (c) Propanone is burned in air
• C3H6O O2 -----gt (1 point)
• C3H6O O2 -----gt CO2 H2O (3
  points)

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Organic ReactionsSample 2

• Halogen substitution with alkanes
• one X replaces one H
• 1982 (e) Methane gas is heated with an excess
  of chlorine gas.
• CH4 Cl2 -----gt (1 point)
• CH4 Cl2 -----gt CH3Cl HCl
  (3 points)

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Organic ReactionsSample 3

• Halogen addition with alkenes alkynes
• X2 is added to the alkene or alkyne.
• 1986 (g) ethene (ethylene) gas is bubbled
  through a solution of bromine.
• C2H4 Br2 -----gt (1 point)
• C2H4 Br2 ----gt C2H4 Br2 (3 points)

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Organic ReactionsSample 4

• Carboxylic acids react with alcohols to form
  esters and water.
• These are similar to acid/base reactions
• R-COOH ROH --gt R-COO-R H2O acid
  alcohol ester

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Organic ReactionsSample 4

• R-COOH ROH -----gt R-COO-R H2O
  acid alcohol ester
• 1985 (c) Ethanol and formic acid (methanoic
  acid) are mixed and warmed.
• C2H5OH HCOOH -----gt (1 point)
• C2H5OH HCOOH -----gt HCOO-C2H5 H2O
  (3 points)

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How to get the highest possible score on Question
4

• 1. Write the reactants in symbol form for
  all eight reactions, showing each reactant in net
  ionic form. Score 5 points
• 2. Classify each reaction.
• 3. Eliminate 3 questions.
• 4. Do your best on the remaining 5 questions.

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How to get the highest possible score on Question
4

• 5. If you get 2 correct your score 9.
• 6. 3 correct and your score is 11.
• These are terrific scores!!!

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Sample Quiz for Question 4

• (a) Sulfur trioxide gas is bubbled into water.
• (b) A solution of potassium phosphate is mixed
  with a solution of calcium acetate.
• (c) A sample of 1-propanol is burned in air.
• (d) A piece of copper wire is placed in a
  solution of silver nitrate.

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Sample Quiz for Question 4

• (e) Powdered barium oxide is added to water.
• (f) Chlorine gas is bubbled through a solution of
  lithium iodide.
• (g) Excess sodium cyanide solution is added to a
  solution of silver nitrate.
• (h) Equal volumes of 0.1 M sulfuric acid and 0.1
  M potassium hydroxide are mixed.

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Sample Quiz for Question 4Answers

• (a) Sulfur trioxide gas is bubbled into water.
• SO3 H2O -----gt H2SO4
• hydrolysis

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Sample Quiz for Question 4Answers

• (b) A solution of potassium phosphate is mixed
  with a solution of calcium acetate.
• PO43- Ca2 -----gt Ca3(PO4)2
• precipitation

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Sample Quiz for Question 4Answers

• (c) A sample of 1-propanol is burned in air.
• C3H7OH O2 -----gt CO2 H2O
• Organic combustion

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Sample Quiz for Question 4Answers

• (d) A piece of copper wire is placed in a
  solution of silver nitrate.
• Cu Ag -----gt Cu2 Ag
• REDOX single replacement

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Sample Quiz for Question 4Answers

• (e) Powdered barium oxide is added to water.
• BaO H2O -----gt Ba2 OH-
• hydrolysis

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Sample Quiz for Question 4Answers

• (f) Chlorine gas is bubbled through a solution of
  lithium iodide.
• Cl2 I- -----gt I2 Cl-
• REDOX single replacement

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Sample Quiz for Question 4Answers

• (g) Excess sodium cyanide solution is added to a
  solution of silver nitrate.
• CN- Ag -----gt Ag(CN)2-
• Ligand

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Sample Quiz for Question 4Answers

• (h) Equal volumes of 0.1 M sulfuric acid and 0.1
  M potassium hydroxide are mixed.
• H OH- -----gt H2O
• Acid/Base

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Questions?