11/11/20131Wed, Nov 13• Lecture 18 (Change)– Reactions that Form Water (7.4)– Reactions Between Metals and Nonmetals (7.5) – Ways to Classify Reactions (7.6)• Questions we’ll answer– What are some common types of chemical reactions?– There are a few different ways to classify chemical reactions. What are they, and why would we need more than one?Acid‐Base Reaction TheoriesArrhenius Theory: – Acids produce H+ions in aqueous solution: – Bases produce OH–ions in aqueous solution: • The Arrhenius theory was limited to bases that contained OH–explicitly, but other species such as ammonia, NH3, also increase OH–. Bronsted‐Lowry: acid/base reactions are proton‐transfer processes.– Acids are proton‐donors (H+ion donor). – Base are proton‐acceptors (H+ion acceptor).• A typical B‐L base is ammonia, NH3: • When NH3 dissolves in water, it increases the concentration of OH–: + + HA HB B + A2HO+ HA H + A2HO+ XO X + OH H+43 + HA NH + ANH 42+3 + HO NH + HNH O11/11/20132Strong AcidsA strong acid completely dissociates in water, giving separate H+ions and anions. Common examples: HCl, HNO3, H2SO4Most foods are acidic: http://www.engineeringtoolbox.com/food‐ph‐d_403.htmlStrong acids are strong electrolytes.The amount of protons in solution is often reported as “pH.”• Acidic: pH < 7.0• Neutral: pH = 7.0• Basic: pH > 7.0Strong BasesIn the Arrhenius definition, a strong base is a metal hydroxide that is completely soluble in water, giving separate OHions and cations. Common examples: NaOH and KOH+ KOHFat moleculeLyeFatty acid salt…soapGlycerol “Lye,” a metal hydroxide salt, is used in the production of soap:Soap molecules form micellesaround grease and oils.NaOH and KOH are strong electrolytes.11/11/20133H2SO4(aq) + NaOH(aq)HCl(aq) + NaOH(aq)Predicting Products of Acid/Base RxnsHNO3(aq) + KOH(aq)Oxidation‐Reduction ReactionsModern definition of “Redox” Chemistry: electron(s) transferr ed from one species to another:• Oxidation: Loss of electrons• Reduction: Gain of electrons (a reduction in oxidation number)OIL RIGOxidation Is Loss of electrons Reduction Is Gain of electronsExample: Glycerol + Potassium Permanganate (http://youtu.be/z_4j36cUcEw)14 KMnO4+ 4  7 K2CO3+ 7 Mn2O3+ 5 CO2+ 16 H2OHistorically, reactions in which oxygen atoms are transferred from one species to another were classified as oxidation‐reduction: • Oxidation: adding oxygen to form an oxide • Reduction: removing oxygen 11/11/20134Oxidation‐Reduction RxnsBefore rxn occurs... During rxnCu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s)Charge: 0 +1 +2 0oxidationreductionCopyright © Cengage Learning. All rights reserved8• Involve oxygen and produce energy (heat) so rapidly that a flame results. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) Special class of oxidation–reduction reactions.Combustion Reactions11/11/20135Oxidation Numbers• An “accounting” of the electrons in a chemical species. This helps us keep track of who is oxidized (loses electrons) and who is reduced (gains electrons).• Oxidation number represents the number of electrons required to produce the charge on a species.The oxidation number...1. ...for any elemental substance is 0 (zero).2. ...for a monatomic ion is its charge (e.g., Mg2+ +2).3. ...for oxygen in a compound is ‐2.4. ...for hydrogen in a compound is +1; for hydride ion (H‐) is ‐1.In molecular/ionic species, the oxidation numbers of the atoms/ions must sum to the total charge.Redox ExamplesFe2O3(s) + 2Al(s)  2Fe(s) + Al2O3(s)Mg(s) + 2HCl(aq)  H2(g) + MgCl2(aq)Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq) 11/11/2013611Reaction Classes• Precipitation: synthesis of an ionic solid– a solid precipitate forms when aqueous solutions of certain ions are mixed• Acid‐Base: proton (H+ion) transfer reactions– acid donates a proton to a base, forming a molecule and an aqueous salt– Acid: proton‐donor; Base: proton‐acceptor• Oxidation‐Reduction: electron transfer reactions– electron transfer from one species to another, causing a change in the oxidation state of the two species– OIL RIG: Oxidation Is Loss (of e‐), Reduction Is Gain (of e‐)3232Pb NO ( ) + 2 KI( ) PbI ( ) + 2 KNO ( )aq aq s aq2HCl( ) + NaOH( ) H O( ) + NaCl( )aq aq l aq332Cu( ) + 2 AgNO ( ) 2 Ag( ) + Cu NO ( )saq s aqClassifying ReactionsThere are two methods of classifying reactions:1. By the type of chemical change that occurs.– i.e., precipitation, acid‐base (proton transfer), oxidation‐reduction (electron transfer)2. By the type of atom rearrangement that occurs.– i.e., decomposition, combination, single‐replacement, double‐replacement The two classification methods can be used to describe the same reaction.11/11/20137Classifying by Chemical Change• Precipitation: synthesis of an ionic solid– a solid precipitate forms when aqueous solutions of certain ions are mixed• Acid‐Base: