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AP Chemistry AP Chemistry Notes - Types of reactions Mr. Ferwerda, Tecumseh HS 06/22/17 Name : Date : I. Introduction to writing AP equations One section of the AP test is always on writing chemical equations. The AP student will be expected to complete three reactions (recommended time allotment during the test is 15 min) in which he/she will have to predict the products, write and balance the equation for the reaction and answer a question regarding the reaction. Aspects of equation writing you should know are : - in all cases a reaction will take place (no "no reaction" answers) - there are no equilibrium ("double arrow") reactions - equations need to be balanced - the symbols (aq), (l), (g), and (s) are not necessary - all equations are to be written as net ionic equations (no spectator ions present) - all aqueous ions are written as aqueous ions (NaCl(aq) is "Na+ + Cl-") - molecular compounds, insoluble compounds, solids,, liquids, and suspended compounds are written in their molecular form (solid NaCl is "NaCl)". - Charges shown on ions must be correct. Each equations is worth five points, one for the correct reactants, two for the correct products and two for the correct answer to the given question. Points are lost for the presence of spectator ions and ionic species written as molecular. Examples : a. Equal volumes of 0.1 M hydrobromic acid and 0.1 M sodium hydroxide are combined. Ans. H+ + OH- H2O b. Magnesium metal is added to a solution of zinc chloride. Ans. Mg + Zn2+ Mg2+ + Zn A. Single replacement (or "single displacement") 1. metal displaces hydrogen from either water or an acid metal + acid salt and hydrogen gas e.g. Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g) (Net : Mg + 2H+ Mg2+ + H2) Group 1A or 2A metal and water base and hydrogen gas e.g. 2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g) (Net : Li + 2H2O Li+ + OH- + H2) 2. a more reactive metal replaces a less reactive metal ion from solution(see activity series) e.g. ZnCl2(aq) + Mg(s) MgCl2(aq) + Zn(s) ( Net : Zn2+ + Mg Mg2+ + Zn ) 3. a halogen replaces another halogen e.g. MgBr2(aq) + F2(g) MgF2(aq) + Br2(l) ( Net : 2 Br - + F2 2 F - + Br2 ) 4. Hydrides of alkali metals react with water to form hydroxides : • e.g. LiH(s) + H2O(l) LiOH + H2(g) (Net : LiH + H2O Li+ + OH- + H2) B. Double replacement (metathesis) (must form precipitate, gas or molecular compound) 1. formation of an insoluble ionic compound (precipitate) -solubility rules will need to be memorized!! Solubility Rules a. Nitrates, chlorates and acetates are soluble. b. Group 1 salts and ammonium salts are soluble. c. Most chloride, bromide and iodide salts are soluble, except for salts of Ag+, Pb2+ and Hg22+. d. Most sulfate salts are soluble. Exceptions include PbSO4, CaSO4, HgSO4 and BaSO4. e. Most hydroxide salts are slightly soluble (will form a precipitate). Ba(OH)2, Sr(OH)2 and Ca(OH) 2 are marginally soluble. f. Most sulfide, chromate, carbonate and phosphate salts are only slightly soluble. e.g. BaCl2(aq) + MgSO4(aq) BaSO4(s) + MgCl2(aq) ( Net :Ba2+ + SO42- BaSO4(s)) AP Chemistry Mr. Ferwerda, Tecumseh HS 06/22/17 2. neutralization reaction between an acid and a base (forms water) Common a. strong acid/strong base : gases : e.g. HCl + NaOH H2O + NaCl (net : H+ + OH- H2O) H2S b. strong acid/weak base CO2 e.g. HCl + NH3 NH4Cl (net : H+ + NH3 NH4+) SO2 e.g. HCl + CH3NH2 CH3NH3Cl (net : H+ + CH3NH2 CH3NH3+) NH3 c. weak acid/strong base e.g. HC2H3O2 + NaOH H2O + C2H3O2- (net : HC2H3O2 + OH- H2O + C2H3O2-) d. weak acids and weak bases e.g. NH3 + HF NH4+ + F- (net) 3. reactions with acids : a. carbonates or bicarbonates and acids form a salt, water and CO2 e.g. 2HCl + Na2CO3 2 NaCl + H2O + CO2 (net : H+ + CO32- H2O + CO2) b. sulfites and acids form a salt, water and SO2 e.g. 2 HCl + Na2SO3 2 NaCl + H2O + SO2 (net : H+ + SO32- H2O + SO2) c. metallic sulfides and acids form H2S and a salt e.g. 2 HCl(aq) + Na2S(aq) 2 NaCl(aq) + H2S(g) (net : H+ + S2- H2S ) d. metallic hydrides and acids form H2 and a salt e.g. HCl(aq) + LiH(aq) LiCl(aq) + H2(g) (net : H+ + H- H2) 4. strong acids with salts of weak acids (salts containing anions such as : OCl-, ClO2-, F-, NO2-, CN-, C2H3O2-) a. metallic acetates and acids form acetic acid and a salt e.g. HCl(aq) + NaC2H3O2(aq) NaCl(aq) + HC2H3O2(aq) (net : H+ + C2H3O2- HC2H3O2) b. metallic nitrites and acids form nitrous acid and a salt e.g. HCl(aq) + NaNO2(aq) HNO2(aq) + NaCl(aq) (net : H+ + NO2- HNO2) 5. reactions with bases : a. ammonium salts and soluble bases yield ammonia, water and a salt e.g. NH4Cl + LiOH NH3 + H2O + LiCl (net : NH4+ + OH- NH3 + H2O) 6. Amides with water e.g. sodium amide and water produce sodium hydroxide and ammonia Net : NaNH2 + H2O Na+ + OH- + NH3 C. Combination 1. metal and nonmetal form a binary ionic compound e.g. 2 Na + F2 2 NaF 2. two nonmetals form a binary covalent compound e.g. S + F2 SF2 3. metal or nonmetal combines with oxygen to form binary ionic or covalent compound e.g. 2 Mg + O2 2 MgO 4. nonmetallic element combines with a binary covalent compound e.g. oxygen and nonmetallic oxide (sulfur dioxide + oxygen sulfur trioxide) e.g. nonmetallic halide and additional halogen ( chlorine trifluoride and fluorine chlorine tetrafluoride) 5. Combination of two compounds a. metallic oxide and nonmetallic oxide form an ionic compound with a polyatomic ion e.g. Na2O + CO2 Na2CO3 b. metal oxides react with water to form hydroxides e.g. CaO + H2O Ca(OH)2 c. nonmetal oxides react with water to form acids e.g. SO2 + H2O H2SO3 (net : SO2 + H2O H+ + HSO3-) d. hydrates result when anhydrous compounds react with water to form hydrates e.g. CuSO4 + 5 H2O CuSO4·5H2O AP Chemistry Mr. Ferwerda, Tecumseh HS 06/22/17 e. Lewis acid (e- pr acceptor) and Lewis base (e- pr. donor) e.g. boron trifluoride (e- deficient) and ammonia (lone pair on N) : BF3 + NH3 BF3NH3 D. Decomposition 1. thermal decomposition a. hydrogencarbonates (bicarbonates) yield carbonates, water and carbon dioxide (relatively low temps) e.g. NaHCO3 Na2CO3 + H2O + CO2 b. carbonates and hydrogen carbonates yield oxides and carbon dioxide (high temp.) e.g. CaCO3 CaO + CO2 c. ammonium carbonate decomposes into ammonia, water and carbon dioxide d. sulfites yield oxides and sulfur dioxide e.g. FeSO3 FeO + SO2 e. oxides, chlorates and perchlorates yield oxygen e.g. 2HgO Hg + O2 e.g. 2KClO3 2KCl + 3O2 e.g. NaClO4 NaCl + 2O2 f. hydroxides, hydrates and some oxyacids release water e.g. Ca(OH)2 CaO + H2O e.g. CuSO4-5H2O CuSO4 + 5 H2O e.g. H2SO3 H2O + SO2 2. Electrolysis - use of electricity to decompose compounds e.g. 2 NaCl 2 Na + Cl2 E. Combustion of hydrocarbons produces water and carbon dioxide e.g. 2 C6H14 + 19 O2 14 H2O + 12 CO2 F. Redox reactions - involve a transfer of electrons (something is oxidized and something else is reduced) and a change of oxidation state. Single replacement and combustion reactions are always redox reactions. Combination and decomposition reactions are sometimes redox reactions. If a reaction takes place in an acidic or basic solution it is most likely a redox reaction. Reactions involving elements in their natural states (e.g. Al, Fe, Cl2, O2, etc.) are redox reactions. 1. Simple redox reactions : a. Hydrogen displacement e.g. Ca(s) + H2O Ca(OH)2(aq) + H2(g) b. Metal displacement e.g. Zn(s) + CuCl2(aq) ZnCl2(aq) + Cu(s) (Net : Zn + Cu2+ Zn2+ + Cu) c. Halogen displacement e.g. Cl2(g) + MgBr2(aq) MgCl2(aq) + Br2(l) (Net : Cl2 + Br- Cl- + Br2) d. Combustion reactions (see above) e. Combination and decomposition reactions (see above) 2. Reactions involving transition metals with multiple oxidation states : • e.g. tin(II) ion with Fe(III) ion (net : Sn2+ + Fe3+ Sn4+ 3. Free halogens in dilute basic solutions form hypohalite ions + Fe2+) • e.g. Cl2(g) + KOH(aq) KClO(aq) + KCl(aq) + H2O(l) (Net : Cl2 + OH- ClO- + Cl- + H2O) 4. Redox reactions involving oxyanions such as Cr2O72 e.g. 14H+(aq) + Cr2O72-(aq) + 6Fe2+(aq) 2Cr3+(aq) + 7 H2O(l) + 6Fe3+ The only way to be able to predict these types of reactions is to become with familiar (i.e. memorize) common oxidizing and reducing agents. See table below. Common Reducing Agents Halide ions Free metals Sulfite ions or SO2 Products formed Free halogen Metal ions Sulfate ions AP Chemistry Mr. Ferwerda, Tecumseh HS 06/22/17 Nitrite ion Nitrate ion Free halogens (dilute basic solution) Hypohalite ions Free halogens (concentrated basic solution) Halate ions Metallous ions (lower oxidation number) Metallic ions (higher oxidation number) Common Oxidizing Agents MnO4- (acidic solution) MnO2 (acidic solution) MnO4- (neutral or basic) Cr2O72- (acidic solution) HNO3 (concentrated) HNO3 (dilute) H2SO4 (hot, concentrated) Metallic ions (high oxidation number) Free halogens Na2O2 HClO4 C2O42H2O2 Products formed Mn2+ Mn2+ MnO2(s) Cr3+ NO2(g) NO(g) SO2(g) Metallous ions (lower oxidation number) Halide ions NaOH ClCO2(g) O2(g) G. Organic reactions 1. Oxidation (combustion reactions) (See E. above) 2. Substitution reactions by halogens • e.g. butane and bromine : C4H10 + Br2 C4H9Br + HBr 3. Esterification - organic acid and alcohol forms an ester and water • e.g. acetic acid and ethanol : CH3COOH + C2H5OH CH3COOC2H5 + H2O 4. Addition : A C=C bond is broken and atoms are attached to the carbon atoms • • e.g. butene and hydrogen gas form butane : C4H8 + H2 C4H10 e.g. hexene and bromine : C6H12 + Br2 C6H12Br2 H. Complexation reactions (coordination chemistry) : (look for terms "excess" or "concentrated") These reactions usually involve transition metal ions bonding to ligands (Lewis bases - electron pair donors) to form complex ions. E.g. Cr(H2O)63+, where the transition metal ion is the Cr3+ ions and the 6 water molecules are the ligands. They are bonded by a coordinate covalent bond which is formed by the sharing of the electron pairs donated by the water molecules. Common ligands and their names : Ligand H2O NH3 ClFBrICNOHNO3NO2O2SO42CH3NH2 (CH3)2NH NO Name aquo ammine chloro fluoro bromo iodo cyano hydroxo nitrato nitro oxo sulfatomethylamine dimethylamine nitrosyl AP Chemistry Mr. Ferwerda, Tecumseh HS CO 06/22/17 carbonyl Examples of cations : [Cr(H2O)6]3+ - hexaaquochromium(III) [Cu(NH3)4]2+ - tetraamminecopper [Ag(NH3)2]+ - diamminesilver [Cr(NH3)5(H2O) ]3+ - pentammineaquochromium(III) Examples of anions : [Cr(H2O)2Cl4]- - diaquotetrachlorochromate(III)* [GaCl3(OH)]- - trichlorohydroxogallate(III) [Al(OH)4]- tetrahydroxoaluminate Examples of compounds : Na[Al(OH)4] sodium tetrahydroxoaluminate *ligands are arranged alphabetically (aquo before chloro) - ligands are named before the metal ion The number of ligands attached to a central metal ion is called the coordination number. e.g. Cr(H2O)63+ has a coordination number of 6. Two, four and six are the most common coordination numbers. The coordination number is often twice the oxidation number of the metallic ion. Ligands are joined one at a time and have a formation constant for each reaction that joins a single ligand. This means that it would take six reactions to form Cr(H2O)63+, each successive reaction joining another water molecule. Likewise, each step would have its own formation constant. Al2O3 + OH- [Al(OH)4] NH3 + Zn2+ [Zn(NH3)4]2+ Fe2+ + SCN- [FeSCN] 2+ Keys to success in equation writing on the AP test : 1. 2. 3. 4. know ion formulas and charges know solubility rules know common oxidizing agents Identify reaction type - remember to add H+ and water to balance redox reactions (watch for term "acidified" indicates redox rxn) - free elements indicate redox reactions 5. Remember amphoteric substances Zn2+ and Al3+ form hydroxides that dissolve in both acids and bases. 6. Leave out spectator ions AP Test instructions : AP Test instructions : " For each of the following three reactions. Write a balanced equation for thte reaction in part (i) and answer the question about the reaction in part (ii). In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You may use the empty space at the bottom of the next page for scratch work, but only equations that are written in the answer boxes provided will be scored" The following website is designed to help you learn the various types of reactions. I highly recommend it. It is challenging and you may be learning by "trial and error" (especially with redox reactions - an emphasis of AP equations) at first, but you will catch on. http://dwb.unl.edu/Chemistry/Desc/Start2.html (login with something like first@timer)