CHEM 1211 Lecture 8 Outline of Last Lecture I Balancing Chemical Equations A Law of Conservation of Matter II Classification of Solutes A Aqueous Solutions B Two Classes of Solutes 1 Electrolytes 2 Non Electrolytes III Chemical Reactions Outline of Current Lecture I Chemical Equilibria II Types of Reactions A Precipitation B Acid Base Neutralization C Gas Forming D Reduction Oxidation III Classifying RXNs Current Lecture I Chemical Equilibria Chemical RXNs always proceed spontaneously toward equilibrium A Dynamic Equilibrium rate of forward rxn rate of reverse rxn Looks like nothing is happening B Product Favored Rxn reactants are completely or largely converted to products reactions proceed to products Most combustion Rxns CH4 2O2 CO2 2H2O C Reactant Favored Rxn only a small amount of reactant is converted to product II Weak Acids Types of Reactions A Precipitation A rxn where an insoluble solid precipitate forms and drops out of the solution Exchange double displacement or metathesis rxns A precipitation produces a water insoluble product known as a precipitate Example Formula unit equation AgNO3 aq KCl aq AgCl s KNO3 aq Total ionic equations Write the formula unit eqn in ionic form Only ionize strong acids bases and soluble salts need to know solubility rules Cannot write as ions if s l or g Ag aq NO3 aq K aq Cl aq AgCl s K aq NO3 aq Net ionic equations Remove spectator ions from both sides A spectator ion is one that doesn t participate in the reaction Ag aq Cl aq AgCl s B Acid Base Neutralization A rxn in which an acid reacts with a base to yield a salt plus water M HCl in stomach Drano solid NaOH with some Al chips Organic acids carboxylic acids occur in nature acetic acid vinegar There are 2 commonly used definitions of acids and bases 1 Arrhenius 2 Bronsted Lowry Arrhenius Theory Acid substance that contains hydrogen and produces H in aqueous solution Acid Examples HCl aq H2O l H3O aq Cl aq HCO2H aq H2O l H3O aq HCO2 aq Base substance that contains hydroxyl OH group and produces hydroxide ions OH in aqueous solutions Base Examples NaOH aq Na aq OH aq Ba OH 2 aq Ba2 aq 2 OH aq Hydronium Ion Hydrated hydrogen ion H aq protons generated in acid base reactions surrounded by solvent water molecules number of water molecules depends on solution H aq is really H H2O n write hydrated hydrogen ion as H3O called hydronium ion Strong Acids and Bases Essentailly 100 ionized in aq soln Weak Acids and Bases Usually 10 ionized in aq soln Bronsted Lowry Theory More general acid base theory acid is proton H donor base is proton H acceptor Examples HBr aq H2O l H3O aq Br aq acid base NH3 aq H2O l base NH4 aq HO aq acid Bronsted Lowry Acid Base Reactions transfer of a proton from an acid to a base Example HCl aq NH3 aq acid NH4 aq Cl aq base Coordinate covalent bonds bonds in which both electrons are supplied by one atom are made in Bronsted Lowry acid base reactions Bronsted Lowry Conjugate Acid Base pairs two species that differ by a proton Example HNO3 H2O H3O conjugate acid 1 conjugate base 2 NO3conjugate acid 2 conjugate base 1 HNO3 is the conjugate acid and NO3 is its conjugate base H2O is the conjugate base and H3O is its conjugate acid Amphiprotic a molecule species can act as an acid and a base Examples 1 H2O and NH3 2 H2O H H3O 3 H2O H OH4 NH3 H NH4 5 NH3 H NH2 Acid Base Theory Comparison Major differences between Arrhenius Bronsted Lowry For Br nsted Lowry theory The reaction does not have to occur in an aqueous solution Bases are not required to be hydroxides Example Acid Base neutralization Reactions formation of the nonelectrolyte H2O acid base salt water Oxides of Nonmetals and Metals Oxides of nonmetals Acidic oxides since they react with H2O to form acids Often called acid anhydrides Oxides of metals Basic oxides since the react with water to form bases Often called base anhydrides C Gas Forming A rxn where an insoluble gas is formed Gas forming reaction Insoluble or slightly soluble gas formed when there are no gaseous reactants Formula unit eqn 2 HCl aq CaCO3 s H2CO3 aq CaCl2 aq CO2 g H2O l Total Ionic 2 H aq 2 Cl aq CaCO3 s H2CO3 aq Ca2 aq 2Cl aq Net Ionic 2 H aq CaCO3 s H2CO3 aq Ca2 aq D Reduction Oxidation A rxn where electrons are transferred from one reactant to another Oxidation increase in oxidation number Reduction decrease in oxidation number reduces ON corresponds to loss of electrons corresponds to gain of electrons Oxidizing agents chemical species that oxidize some substance contain atoms that are reduced in the reaction gain electrons Reducing agents chemical species that reduce some substance contain atoms that are oxidized in the reaction lose electrons Examples KMnO4 and Fe2 Fe2 added to purple KMnO4 Fe2 is oxidized to Fe3 Fe2 Fe3 are colorless Mn2 is colorless MnO41 is reduced to Mn2 ON of Mn in MnO41 is 7 8H 5Fe2 MnO41 5Fe3 Mn2 4H2O Assigning Oxidation Numbers Example 1 NaNO3 Example 2 K2Sn OH 6 Which species are oxidized and reduced Which species are oxidized and reduced What are the oxidizing and reducing agents formula unit 2 H2SO3 aq O2 g 2 H2SO4 aq Oxidation numbers H 1 S 4 O 2 O 0 H 1 S 6 O 2 SO32 is oxidized S from 4 to 6 O2 is reduced O from 0 to 2 H2SO3 is reducing agent O2 is oxidizing agent III Classifying RXNs Precipitation reaction ions in reactants combine to form insoluble reaction product Acid base reaction water is often product cation and anion combine to form salt Gas forming reaction gas leaves solution often involve carbonates sulfites of sulfides Oxidation reduction Electron transfer reaction in which one reactant is reduced and another is oxidized