Predicting Reaction Products - Question 4 David Lee Retired AP Chemistry Teacher 35 years at Mountain Lakes HS 11/23/2018

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.” 11/23/2018

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. 11/23/2018

Agenda Why are we here? Classification of reactions Sample reactions How to get the highest possible score A short quiz (won’t be scored) Q & A May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

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 May 22, 2004 Predicting Reaction Products

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 May 22, 2004 Predicting Reaction Products

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 May 22, 2004 Predicting Reaction Products

Classification of Reactions Acid/Base Precipitation Hydrolysis Decomposition (& reversed) Ligands REDOX Organic May 22, 2004 Predicting Reaction Products

Acid/Base Reactions HX + MOH ----> MX + HOH Weak acids & weak bases must be written as molecules Strong acids & strong bases must be written as ions. May 22, 2004 Predicting Reaction Products

Acid/Base Reactions Soluble salts (MX) are completely ionized in water. Remove spectator ions & write the net ionic equation. May 22, 2004 Predicting Reaction Products

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 ----> (1 point scored for correct reactants) May 22, 2004 Predicting Reaction Products

Acid/Base Reaction Sample #1 H2SO4 + KOH ---> K2SO4 + HOH (scores 2 points total since it is NOT written as a net ionic equation) H+ + OH- ----> HOH (scores all 3 points since it is a net ionic equation) May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

Acid/Base Sample #2 H3PO4 + KOH ----> (1 point) H3PO4 + KOH ----> KH2PO4 + HOH (2 points - NOT net ionic) May 22, 2004 Predicting Reaction Products

Acid/Base Sample #2 H3PO4 + OH- ----> H2PO4- + HOH (3 points) H3PO4 + OH- ----> PO43- + HOH (2 points - does NOT show equimole relationship) May 22, 2004 Predicting Reaction Products

Precipitation Reactions One or more products is(are) not significantly soluble in water. Generally both reactants are salts in solution May 22, 2004 Predicting Reaction Products

Precipitation Reactions General equation: AX + BY -----> AY + BX Where AY and/or BX is(are) insoluble in water May 22, 2004 Predicting Reaction Products

Precipitation Reactions Net ionic equation: A+ + Y- -----> AY where AY is insoluble in water & BX is soluble in water May 22, 2004 Predicting Reaction Products

Precipitation Reactions Sample #1 2003B (d) A solution of lead(II) nitrate is added to a solution of potassium sulfate. Pb(NO3)2 + K2SO4 -----> (scores 1 point for correct reactants) May 22, 2004 Predicting Reaction Products

Precipitation Reactions Sample #1 Pb(NO3)2 + K2SO4 -----> PbSO4 + KNO3(scores 2 points for correct answer but not in net ionic form) Pb2+ + SO42- -----> PbSO4 (scores 3 points for correct net ionic answer) May 22, 2004 Predicting Reaction Products

Precipitation Reactions Sample #2 2002 (a) A solution of sodium iodide is added to a solution of lead(II) acetate. NaI + Pb(C2H3O2)2 ----> (1 point) NaI + Pb(C2H3O2)2 ----> PbI2 + Na C2H3O2 (2 points since it is NOT net ionic) May 22, 2004 Predicting Reaction Products

Precipitation Reactions Sample #2 I- + Pb2+ ----> PbI2 (3 points for net ionic equation) May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

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 -----> (1 point) Cs2O + H2O -----> CsOH (2 points) Cs2O + H2O -----> Cs+ + OH- (3 points) May 22, 2004 Predicting Reaction Products

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 -----> (1 point) N2O5 + H2O -----> HNO3 (2 points) N2O5 + H2O -----> H+ + NO3- (3 points) May 22, 2004 Predicting Reaction Products

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 -----> (1 point) CaH2 + H2O -----> Ca(OH)2 + H2 (2 points) May 22, 2004 Predicting Reaction Products

Hydrolysis Reaction Sample #3 CaH2 + H2O -----> Ca2+ + OH - + H2 (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reactions A lone compound is strongly heated, exposed to strong sunlight or electric current. May 22, 2004 Predicting Reaction Products

Decomposition Reactions Compounds that readily decompose: Metallic carbonates Most metallic hydroxides Metallic chlorates Metallic sulfites Some acids Peroxides Electrolysis of salts May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #1 Metallic carbonates decompose to form a metallic oxide & carbon dioxide. 1996 (a) Solid calcium carbonate is strongly heated. CaCO3 -----> (1 point) CaCO3 -----> CaO + CO2 (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #2 Most metallic hydroxides, when strongly heated, form metal oxides and water. Solid calcium hydroxide is strongly heated. Ca(OH)2 -----> (1 point) Ca(OH)2 -----> CaO + H2O (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #3 Metallic chlorates, when strongly heated, form metallic chlorides and oxygen gas. Solid potassium chlorate is strongly heated. KClO3 -----> (1 point) KClO3 -----> KCl + O2 (3 points) May 22, 2004 Predicting Reaction Products

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 -----> (1 point) CaSO3 -----> CaO + SO2 (3 points) May 22, 2004 Predicting Reaction Products

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 -----> (1 point) H2CO3 -----> CO2 + H2O (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #6 Sulfurous acid readily decomposes in water solution to form sulfur dioxide and water. H2SO3 -----> (1 point) H2SO3 -----> SO2 + H2O (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #7 Hydrogen peroxide decompose into water and oxygen gas. H2O2 -----> (1 point) H2O2 -----> H2O + O2 (3 points) May 22, 2004 Predicting Reaction Products

Decomposition Reaction Sample #8 Electrolysis of molten salts produces elements from the ions. Molten magnesium bromide is electrolyzed using inert electrodes. MgBr2 -----> (1 point) MgBr2 -----> Mg + Br2 (3 points) Since water is not present MgBr2 is not written as separate ions. May 22, 2004 Predicting Reaction Products

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-) May 22, 2004 Predicting Reaction Products

Ligand Reactions General rule: The number of ligands attached to the metallic anion is usually DOUBLE the anion’s charge. Ag(NH3)2+ Cu(NH3)42+ Fe(NH3)63+ Ag+ Cu2+ Fe3+ May 22, 2004 Predicting Reaction Products

Ligand Reactions Sample #1 2003 (e) Excess concentrated aqueous ammonia is added to solid silver chloride. NH3 + AgCl -----> (1 point) NH3 + AgCl -----> Ag(NH3)2+ + Cl- (3 points) May 22, 2004 Predicting Reaction Products

Ligand Reactions Sample #2 1989 (f) A solution of ammonium thiocyanate is added to a solution of iron(III) chloride. NH4SCN + FeCl3 -----> (1 point) NH4SCN + FeCl3 -----> (NH4)3 Fe(SCN)6 + NH4Cl (2 points) May 22, 2004 Predicting Reaction Products

Ligand Reactions Sample #2 SCN- + Fe3+ -----> Fe(SCN)63- (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions REDOX reactions make up about 33% of the Question 4. That’s 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.” May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #1 Sample: Composition reactions where metal + nonmetal elements react to form a compound. 2003 (f) Magnesium ribbon is burned in oxygen. Mg + O2 -----> (1 point) Mg + O2 -----> MgO (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #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 -----> (1 point) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #2 Sr + Cu(NO3)2 -----> Sr(NO3)2 + Cu (2 points) Sr + Cu2+ -----> Sr2+ + Cu (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #3 Sample: Single replacement reactions where halogen replaces the halide from a halide salt. May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #3 2001 (f) Chlorine gas is bubbled through a solution of potassium bromide. Cl2 + KBr -----> (1 point) Cl2 + KBr -----> KCl + Br2 (2 points) Cl2 + Br- -----> Cl- + Br2 (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #4 2002 (g) Acidified solutions of potassium permanganate and iron(II) nitrate are mixed together. H+ + KMnO4 + Fe(NO3)2 -----> (1 point) H+ + KMnO4 + Fe(NO3)2 -----> Fe (NO3)3 + Mn (NO3)2 + H2O (2 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #4 H+ + MnO4- + Fe2+ -----> Fe3+ + Mn2+ + H2O (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #5 2001 (e) A solution of iron(II) chloride is added to an acidified solution of sodium dichromate. FeCl2 + H+ + Na2Cr2O7 -----> (1 point) FeCl2 + H+ + Na2Cr2O7 -----> FeCl3 + CrCl3 + NaCl + H2O (2 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #5 Fe2+ + H+ + Cr2O72- -----> Fe3+ + Cr3+ + H2O (3 points) May 22, 2004 Predicting Reaction Products

REDOX Reactions Sample #6 1993 (a) A strip of copper is immersed in dilute nitric acid Cu + HNO3 ----> (1 point) Cu + HNO3 ----> Cu(NO3)2 + NO + H2O (2 points) Cu + H+ + NO3- ----> Cu2+ + NO + H2O (3 points) May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

Organic Reactions Sample #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 -----> (1 point) C3H6O + O2 -----> CO2 + H2O (3 points) May 22, 2004 Predicting Reaction Products

Organic Reactions Sample #2 Halogen substitution with alkanes one X replaces one H 1982 (e) Methane gas is heated with an excess of chlorine gas. CH4 + Cl2 -----> (1 point) CH4 + Cl2 -----> CH3Cl + HCl (3 points) May 22, 2004 Predicting Reaction Products

Organic Reactions Sample #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 -----> (1 point) C2H4 + Br2 ----> C2H4 Br2 (3 points) May 22, 2004 Predicting Reaction Products

Organic Reactions Sample #4 Carboxylic acids react with alcohols to form esters and water. These are similar to acid/base reactions R-COOH + R’OH --> R-COO-R’ + H2O acid alcohol ester May 22, 2004 Predicting Reaction Products

Organic Reactions Sample #4 R-COOH + R’OH -----> R-COO-R’ + H2O acid alcohol ester 1985 (c) Ethanol and formic acid (methanoic acid) are mixed and warmed. C2H5OH + HCOOH -----> (1 point) C2H5OH + HCOOH -----> HCOO-C2H5 + H2O (3 points) May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

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!!! May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

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. May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (a) Sulfur trioxide gas is bubbled into water. SO3 + H2O -----> H2SO4 hydrolysis May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (b) A solution of potassium phosphate is mixed with a solution of calcium acetate. PO43- + Ca2+ -----> Ca3(PO4)2 precipitation May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (c) A sample of 1-propanol is burned in air. C3H7OH + O2 -----> CO2 + H2O Organic combustion May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (d) A piece of copper wire is placed in a solution of silver nitrate. Cu + Ag+ -----> Cu2+ + Ag REDOX single replacement May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (e) Powdered barium oxide is added to water. BaO + H2O -----> Ba2+ + OH- hydrolysis May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (f) Chlorine gas is bubbled through a solution of lithium iodide. Cl2 + I- -----> I2 + Cl- REDOX single replacement May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (g) Excess sodium cyanide solution is added to a solution of silver nitrate. CN- + Ag+ -----> Ag(CN)2- Ligand May 22, 2004 Predicting Reaction Products

Sample Quiz for Question 4 Answers (h) Equal volumes of 0.1 M sulfuric acid and 0.1 M potassium hydroxide are mixed. H+ + OH- -----> H2O Acid/Base May 22, 2004 Predicting Reaction Products

Questions? May 22, 2004 Predicting Reaction Products