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Each reaction will usually be worth a total of 5 points.

ulric-padilla
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Each reaction will usually be worth a total of 5 points.

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  1. WRITING AP EQUATIONSAP equation sets are found in the free-response section of the AP test. You are given three sets of reactants and you must write balanced net ionic equations for the reaction that would occur. The equations are of mixed types. You will also answer a short question about each reaction. The section is worth 15 points and is 15 % of the free response grade. Free response is 50% of the total AP test grade.

  2. All AP equations "work". In each case, a reaction will occur. These equations need to be written in net ionic form. All spectator ions must be left out and all ions must be written in ionic form. All molecular substances and insoluble compounds must be written together (not ionized!). Know your solubility rules!!!

  3. Ca(OH)2 and Sr(OH)2 are moderately soluble and can be written together or as ions. Ba(OH)2 is soluble and Mg(OH)2 is insoluble. CaSO4 and SrSO4 are moderately soluble and can be written together or as ions.BaSO4 is insoluble and MgSO4 is soluble.

  4. Weak electrolytes, such as acetic acid, are not ionized. Solids and pure liquids are written together, also. A saturated solution is written in ionic form while a suspension is written together.

  5. Each reaction will usually be worth a total of 5 points. General guidelines (may not always be true!): One point is given for the correct reactants and two points for all correct products. If a reaction has three products, one point is given for two correct products and two points for all correct products. One point will be given for correct balancing and the final point will be given for correctly and completely answering the question concerning the reaction.

  6. The best way to prepare for the equation section of the AP test is to practice lots of equations. The equation sets are similar and some equations show up year after year. Save the reactions that you write and practice them again before the AP test in May.

  7. When you are reading an equation, first try to classify it by type. If it says anything about acidic or basic solution, it is redox. If you are totally stuck, look up the compounds in the index of your book or other reference books and try to find information that will help you with the equation. All reactions do not fit neatly into the fivetypes of reactions that you learned in Chemistry I.

  8. Double Replacement (metathesis)

  9. Two compounds react to form two new compounds. No changes in oxidation numbers occur. All double replacement reactions must have a "driving force" that removes a pair of ions from solution.

  10. Formation of a precipitate: A precipitate is an insoluble substance formed by the reaction of two aqueous substances. Two ions bond together so strongly that water can not pull them apart. You must know your solubility rules to write these net ionic equations!

  11. Ex. Solutions of silver nitrate and lithium bromide are mixed. AgNO3(aq) + LiBr(aq)  AgBr(s) + LiNO3(aq) Ag+ + NO3- + Li+ + Br- AgBr + Li+ +NO3- Ag+ + NO3- + Li+ + Br- AgBr + Li+ +NO3- Ag+ + Br- AgBr

  12. Formation of a gas: Gases may form directly in a double replacement reaction or can form from the decomposition of a product such as H2CO3 or H2SO3.

  13. Ex. Excess hydrochloric acid solution is added to a solution of potassium sulfite. 2HCl(aq) + K2SO3(aq) H2SO3 H2O(l) + SO2(g) + 2KCl(aq) 2H+ + 2Cl- + 2K+ + SO32- H2O + SO2 + 2K+ +2Cl- 2H+ + 2Cl- + 2K+ + SO32- H2O + SO2 + 2K+ +2Cl- 2H+ + SO32-  H2O + SO2

  14. Ex. A solution of sodium hydroxide is added to a solution of ammonium chloride. NaOH(aq) + NH4Cl(aq) NaCl(aq) + NH4OH NH3(g) + H2O(l) Na+ + OH- + NH4+ + Cl-  Na+ + Cl- +NH3 + H2O Na+ + OH- + NH4+ + Cl-  Na+ + Cl- +NH3 + H2O OH- + NH4+ NH3 + H2O

  15. Formation of a molecular substance:When a molecular substance such as water or acetic acid is formed, ions are removed from solution and the reaction "works".

  16. Ex. Dilute solutions of lithium hydroxide and hydrobromic acid are mixed. LiOH(aq) + HBr(aq)  LiBr(aq) +H2O(l) Li+ + OH- + H+ + Br- Li+ +Br- + H2O Li+ + OH- + H+ + Br- Li+ +Br- + H2O OH- + H+ H2O(HBr, HCl, and HI are strong acids)

  17. Ex. Gaseous hydrofluoric acid reacts with solid silicon dioxide. 4HF(g) + SiO2(s) SiF4(g) + 2H2O(l) 4HF + SiO2 SiF4 + 2H2O 4HF + SiO2 SiF4 + 2H2O

  18. Single Replacement

  19. Reaction where one element displaces another in a compound. One element is oxidized and another is reduced. A + BC  B + AC

  20. Active metals replace less active metals or hydrogen from their compounds in aqueous solution.Usean activity series or a reduction potential table to determine activity. The more easily oxidized metal replaces the less easily oxidized metal. The metal with the most negative reduction potential will be the most active.

  21. Ex. Magnesium turnings are added to a solution of iron(III) chloride. 3Mg(s) + 2FeCl3(aq) 2Fe(s)+3MgCl2(aq) 3Mg + 2Fe3+ + 6Cl- 2Fe + 3Mg2+ + 6Cl- 3Mg + 2Fe3+ + 6Cl- 2Fe + 3Mg2+ + 6Cl- 3Mg + 2Fe3+ 2Fe + 3Mg2+ Always make sure that charge is balanced, as well as mass (atoms)!

  22. Ex. Sodium is added to water. 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) 2Na + 2H2O  2Na+ + 2OH- + H2 2Na + 2H2O  2Na+ + 2OH- + H2 Alkali metal demo

  23. Active nonmetals replace less active nonmetals from their compounds in aqueous solution. Each halogen will displace less electronegative (heavier) halogens from their binary salts.

  24. Ex. Chlorine gas is bubbled into a solution of potassium iodide. Cl2(g) + 2KI(aq) 2KCl(aq) + I2(s) Cl2 + 2K+ + 2I- 2K+ + 2Cl- + I2 Cl2 + 2K+ + 2I- 2K+ + 2Cl- + I2 Cl2 + 2I- I2 + 2Cl-

  25. Anhydrides

  26. Anhydride means "without water".Water is a reactant in each of these equations.

  27. Nonmetallic oxides (acidic anhydrides) plus water yield acids.

  28. Ex. Carbon dioxide is bubbled into water. CO2 + H2O  H2CO3

  29. Metallic oxides (basic anhydrides) plus water yield bases.

  30. Ex. Solid sodium oxide is added to water. Na2O + H2O  2Na+ + 2OH-

  31. Metallic hydrides (ionic hydrides) plus water yield metallic hydroxides and hydrogen gas.

  32. Ex. Solid sodium hydride is added to water. NaH + H2O  Na+ + OH- + H2

  33. Phosphorus halides react with water to produce an acid of phosphorus (phosphorous acid or phosphoric acid) and a hydrohalic acid. The oxidation number of the phosphorus remains the same in both compounds. Phosphorus oxytrichloride reacts with water to make the same products.

  34. Ex. Phosphorus tribromide is added to water. PBr3 + 3H2O  H3PO3 + 3H++ 3Br-

  35. Group I&II nitrides react with water to produce the metallic hydroxide and ammonia.

  36. Amines react with water to produce alkylammonium ions and hydroxide ions.

  37. Ex. Methylamine gas is bubbled into distilled water. CH3NH2 + H2O CH3NH3+ + OH-

  38. OXIDATION-REDUCTION REACTIONS

  39. Redox reactions involve the transfer of electrons. The oxidation numbers of at least two elements must change. Single replacement, some combination and some decomposition reactions are redox reactions.

  40. To predict the products of a redox reaction, look at the reagents given to see if there is both an oxidizing agent and a reducing agent. When a problem mentions an acidic or basic solution, it is probably redox.

  41. Common oxidizing agents Products formedMnO4- in acidic solution Mn2+ MnO2 in acidic solution Mn2+ MnO4- in neutral or basic solution MnO2(s)Cr2O72- in acidic solution Cr3+HNO3, concentrated NO2 HNO3, dilute NO H2SO4, hot, concentrated SO2

  42. Common oxidizing agents Products formedmetal-ic ions metal-ous ionsfree halogens halide ions Na2O2 NaOH HClO4 Cl- H2O2 H2O

  43. Common Products reducing agentsformedhalide ionsfree halogen free metalsmetal ions sulfite ions or SO2 sulfate ionsnitrite ions nitrate ionsfree halogens, dilute basic solution hypohalite ionsfree halogens, conc. basic solution halate ionsmetal-ous ions metal-ic ions  H2O2 O2 C2O42- CO2

  44. Ex. A solution of tin(II) chloride is added to an acidified solution of potassium permanganate. 5Sn2+ + 16H+ + 2MnO4-5Sn4+ + 2Mn2+ + 8H2O

  45. Ex. A solution of potassium iodide is added to an acidified solution of potassium dichromate. 6I- + 14H+ + Cr2O72-2Cr3+ + 3I2 + 7H2O

  46. Ex. Hydrogen peroxide solution is added to a solution of iron(II) sulfate. H2O2 + 2Fe2+ +2H+ 2Fe3+ + 2H2O

  47. Ex. A piece of iron is added to a solution of iron(III) sulfate. Fe + 2Fe3+ 3Fe2+

  48. Tricky redox reactions that appear to be ordinary single replacement reactions:Hydrogen reacts with a hot metallic oxide to produce the elemental metal and water.

  49. Ex. Hydrogen gas is passed over hot copper(II) oxide. H2(g) + CuO(s)  Cu(s)+ H2O(l)

  50. A metal sulfide reacts with oxygen to produce the metallic oxide and sulfur dioxide.

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