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Predicting Reactions

Predicting Reactions

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Predicting Reactions

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  1. Predicting Reactions Presented by Mr. Mark Langella AP Chemistry Instructor College Board Consultant And Dr. Robert Gamper AP Chemistry Instructor 9/9/2014 Sponsored by

  2. Why do the reactions occur? • Gibbs Free Energy drives the Spontaneous reactions • Lower PE energy • Formation of Stronger Bonds • Greater Entropy ( Formation of Gases) • Solubility • Formation Constant Sponsored by

  3. Ways of Expressing CHEMICAL EQUATIONS • Word equation • In word equations, the names of the reactants and products are written out. The following example is a word equation: • carbon + oxygen carbon dioxide Sponsored by

  4. Formula equations • Formula equations consist of formulas substituted for the names in the word equation. The reaction above becomes • C + O2 CO2 Sponsored by

  5. Ionic equations • In ionic equations, all water soluble compounds in an aqueous solution are separated into ions. • 2NaI(aq) + Pb(NO3)2(aq) 2NaNO3(aq) + PbI2(s) • 2Na+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) 2Na+(aq) + 2NO3-(aq) + PbI2(s) • Spectator ions - Spectator ions do not participate in the chemical reaction. That is, they are identical on both sides of the equation. Sponsored by

  6. Net ionic equations • The net ionic equation contains all of the particles in the ionic equation less any spectator ions. • 2Na+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) 2Na+(aq) + 2NO3-(aq) + PbI2(s) • Pb2+(aq) + 2I-(aq) PbI2(s) Sponsored by

  7. Changes to Format • 3 questions, no choices • The equations will still be "net ionic" as they always have been, just balanced. • There will, as the acorn book also states, be a small question about the reaction that the student will have to answer. • The exact point values are not determined yet, the majority of the weight for each part will be on the balanced equation, rather than on the question. • The stems of the questions in some cases contain a little more guidance than we have seen in the past--for example, the equation on this year's question 4 that involves the addition of hydrochloric acid to silver chloride next year will be asked in such a way that the students are guided toward the formation of a complex. • The questions are simple things like what our students already are seeing on the multiple choice. • Posted on AP Central soon . Look for it there. Sponsored by

  8. Changes to Format • The scoring changes have reduced the weight of this section to about 5% of the overall points available on the exam. • The student must write the balanced net ionic equation and then answer a question about the reaction. •  Points would be given for correct reactants, correct products, correct balancing, and the correct answer to the question asked. • The majority of the points available will be given for the correct balanced equation. Sponsored by

  9. Examples • 1. A strip of magnesium metal is added to an aqueous solution of silver nitrate.        Question: Which substance is oxidized in the reaction?2. Solid potassium chlorate is strongly heated.        Question: What is the oxidation number of chlorine before and after the reaction occurs?3. Solid silver chloride is added to a solution of concentrated hydrochloric acid to form a complex ion.        Question: Which species acts as a Lewis base in the reaction?  Explain.4.  A solution of ethanoic (acetic) acid is added to a solution of barium hydroxide.        Question: Explain why a mixture of equal volumes of equimolar solutions of acetic acid and barium hydroxide is basic. Sponsored by

  10. Examples • 5. Ammonia gas is bubbled into a solution of hydrofluoric acid.        Question: Identify a conjugate acid-base pair in the reaction.6. Zinc metal is placed into a solution of copper (II) sulfate.        Question: Describe the change in color that the original solution undergoes as the reaction proceeds.7. Hydrogen phosphide (phosphine) gas is added to boron trichloride gas.        Question: Which species acts as a Lewis acid in the reaction? Explain. Sponsored by

  11. Examples • 8. A solution of nickel (II) bromide is added to a solution of potassium hydroxide.        Question: Identify the spectator ions in the reaction mixture.9. Hexane is combusted in air.        Question: When one molecule of hexane is completely combusted, how many molecules of products are formed? •,3046,151-165-0-52321,00.html Sponsored by

  12. Balancing • We were reminded (especially by the combustion reaction above) that the coefficients used for balancing should be the lowest possibleWHOLE NUMBER coefficients.   • All other rules for the balanced equations are the same - omit spectator ions, assume a reaction occurs, write the formulas for molecular compounds (e.g. HF) as undissociated species in solution, etc. Sponsored by

  13. Synthesis or Combination Reactions • In synthesis or combination reactions, two or more substances combine together to form a single product. • The general form is A + B C • The products must contain only those elements found in the reactants. Sponsored by

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  15. Metal + Nonmetal Salt • Magnesium ribbon is burned in oxygen • A strip of magnesium metal is heated strongly in pure nitrogen gas Sponsored by

  16. Online Demos • Reaction of Magnesium and Oxygen • • Reaction of Iron and Sulfur • • Reaction of Potassium and Oxygen • • Reaction of Lithium and Oxygen • • Reaction of Lithium and Chlorine • • Reaction of Sodium and Oxygen • • Reaction of Zinc and Sulfur • Sponsored by

  17. Nonmetal + Nonmetal Molecular compounds • Pure Solid Phosphorus (White Form) is burned in air • Reaction of Phosphorus and Chlorine • Website: • Reaction of Hydrogen and Oxygen • Website: Sponsored by

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  19. Hydrides • Preparation of the Group 1 hydrides • These are made by passing hydrogen gas over the heated metal. For example, for lithium hydride: Sponsored by

  20. Nonmetal Oxide + Water Oxyacid • Oxy Acid= Contains H+ ions attached to common Polyatomic ion of Nonmetal Oxide plus one more oxygen • Solid dinitrogen pentoxide is added to water • Sulfur trioxide gas is bubbled into water Sponsored by

  21. Phosphorus(V) oxide powder is sprinkled over dis­tilled water • Sulfur dioxide gas is bubbled into distilled water Sponsored by

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  23. Metal oxide + water metal hydroxide • Solid Cesium Oxide is added to water • Solid sodium oxide is added to distilled water • Powdered strontium oxide is added to distilled water • Calcium oxide powder is added to distilled water • Solid barium oxide is added to distilled water Sponsored by

  24. Demo Sponsored by

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  26. Nonmetal Oxide and Metal Hydroxide • ) Reaction of Carbon Dioxide and Limewater • Website: • CO2(g) + Ca(OH)2(l)  CaCO3(s) + H2O(l) Sponsored by

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  28. Hydrogen-Nonmetal + Water Acidic Solution • Hydrogen Chloride gas bubbled into water Sponsored by

  29. Metal oxide + nonmetal oxide metal ion attached to common polyatomic ion • Metal oxide + carbon dioxide metal carbonate • Carbon dioxide gas is passed over hot, solid sodium oxide • Metal oxide + sulfur dioxide Metal sulfite • Sulfur Dioxide is passed over solid calcium oxide Sponsored by

  30. DECOMPOSITION REACTIONS • Substances break down by means of decomposition reactions • The general form of a decomposition reaction is • C A + B • Decomposition reactions are the opposite of combination or synthesis reactions Sponsored by

  31. Decomposition of Metal Carbonate • Heating a metal carbonate always yields the metal oxide and carbon dioxide. • MCO3 MO + CO2 • Powdered magnesium carbonate is heated strongly • Solid calcium carbonate is strongly heated Sponsored by

  32. Metal Hydrogen Carbonate Decomposition • Heating a metal bicarbonate gives the metal oxide, carbon dioxide, and water. • MHCO3 MO + H2O + CO2 • • Solid Sodium Hydrogen Carbonate is strongly heated Sponsored by

  33. Heating the nitrates • Most nitrates tend to decompose on heating to give the metal oxide, brown fumes of nitrogen dioxide, and oxygen. • For example, a typical Group 2 nitrate like magnesium nitrate decomposes like this: • In Group 1, lithium nitrate behaves in the same way - producing lithium oxide, nitrogen dioxide and oxygen. • The rest of the Group, however, don't decompose so completely (at least not at Bunsen temperatures) - producing the metal nitrite and oxygen, but no nitrogen dioxide. Sponsored by

  34. Decomposition of Metal Hydroxides • Heating a metal hydroxide gives the metal oxide and water • MOH MO + H2O Sponsored by

  35. Metal Sulfite Decomposition • Heating a metal sulfite produces a metal oxide and sulfur dioxide • MSO3 MO + SO2 • Solid calcium sulfite is heated in a vacuum Sponsored by

  36. Metal Chlorate Decomposition • Heating a metal chlorate gives the metal chloride plus oxygen. • MClO3 MCl + O2 • Shortcut to Combustion of a peanut M&M • Burning Gummi Bears • Website: Sponsored by

  37. Electrolysis of Binary Compound • Electrolysis of a molten salt (ionic compound) separates the substance into its elements. • MN M + N Sponsored by

  38. Ammonium Compound Decomposition • Ammonium Carbonates • Solid ammonium carbonate is heated • Ammonium Hydroxide Sponsored by

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  40. Ammonium Dichromate Volcano • Website: • Decomposition of Ammonium Dichromate • Website: • (NH4)2Cr2O7(s)  Cr2O3(s) + N2(g) + 4H2O(g) Sponsored by

  41. Peroxide Decomposition • Elephant’s Toothpaste • Website: • Genie in a Bottle Demo • Website: Sponsored by

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  43. Reactions Based on Reduction Potentials EMF Potential • Reduction and Oxidation • Single replacement Sponsored by

  44. Cation Replacement • There are two types of single replacement reactions, in one, a metal or hydrogen replaces a positive ion • M0 + A+B- M+B- + A0 Sponsored by

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  46. Replacement of Hydrogen • Reaction of Magnesium and Different Concentrations of Acids • Website: • Hydrochloric Acid(g) + Magnesium(s)  Magnesium(II)Chloride(aq) + Hydrogen(g) • 2HCl(g) + Mg(s)  MgCl2(aq) + H2(g) • Small piece of sodium metal is added to distilled water • Website: • Sodium(s) + Water(l)  Sodium Hydroxide(aq) + Hydrogen(g) • 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) Sponsored by

  47. ) Reaction of Potassium and Water • Website: • Potassium(s) + Water(l)  Potassium Hydroxide(aq) + Hydrogen(g) • 2K(s) + 2H2O  2KOH + H2(g) • A strip of zinc is added to a solution of 6.0-molar hydrobromic acid • Group I with water video • Sponsored by

  48. Cation Replacement • Reaction of Zinc and Tin (II) Chloride • Website: • Zinc(s) + Tin (II) Chloride(aq)  Tin(s) + Zinc (II) Chloride(aq) • Zn(s) + SnCl2(aq)  Sn(s) + ZnCl2(aq) Sponsored by

  49. Thermite Reaction • 2Al(s) + Fe2O3 (s)  Al2O3 (s) + 2Fe(l) • • Sponsored by

  50. A solution of copper(II) sulfate is spilled onto a sheet of freshly polished aluminum metal. • Bar of strontium metal is immersed in a 1.0 M copper (II) nitrate solution. • A piece of copper wire is placed in a solution of silver nitrate • A small piece of calcium metal is added to hot distilled water • A solution of tin(II) nitrate is added to a solution of silver nitrate Sponsored by