I A 1 2 3 B 1 Chapter 9 Chemical Reactions in Aqueous Solutions We will not cover gravimetric analysis in Section 9 6 General Properties of Aqueous Solutions Definitions Solution is a homogeneous mixture of two or more substances Solutions can be gases liquids or solids Solvent is the substance present in the larger amount that does the dissolving Solute is the substance present in the smaller amount that is dissolved Electrolytes and Nonelectrolytes Electrolytes are substances that when dissolved in water conduct electric current a b c d Solutions of ionic compounds are electrolytes When an ionic compound dissolves it dissociates into its component ions The ions present in the solution are the species that conduct the current Some molecular compounds such as HCl and NH3 react with water and form ions and are conductors HCl g H2O H3O aq Cl aq acid NH3 g H2O NH4 aq OH aq base e Nonelectrolytes are substances that dissolve in water but do not ionize These are present as molecules in aqueous solution H2O C12H22O11 s C12H22O11 aq 2 Strong and Weak Electrolytes a A strong electrolyte is a substance that dissociates completely in water into its component ions H2O KCl s K aq Cl aq HBr aq H aq Br aq 1 b A weak electrolyte is a molecular substance that ionizes partially forms a few ions but most of it remains in the unionized form as molecules In weak electrolytes the unionized species are in equilibrium with the ions 1 Many acids are weak electrolytes such as acetic acid and ionize as shown HC2H3O2 aq H2O H3O aq C2H3O2 aq 2 Weak bases are also weak electrolytes such as ammonia NH3 g H2O NH4 aq OH aq 3 Guide to determining whether a Solution is a Strong Weak or Nonelectrolyte Strong electrolytes are ionic compounds strong acids and strong bases Ionic compounds a b Contain a cation which is either a metal ion or NH4 and an anion which may be monatomic or polyatomic A binary compound that contains a metal and a nonmetal is almost always ionic Strong acids Strong bases HCl HNO3 H2SO4 Group 1A hydroxides and Ba OH 2 HBr HClO3 HI HClO4 Weak electrolytes are weak acids and weak bases Weak acids are Molecular compounds that contain an ionizable hydrogen and nonmetal atoms Weak bases are Derivatives of NH3 HC2H3O2 acetic acid H2CO3 carbonic acid H3PO4 phosphoric acid HNO2 nitrous acid CH3NH2 C5H5N NH2OH methylamine pyridine hydroxylamine Nonelectrolytes are molecular substances that do not ionize when dissolved in water such as sugar 2 II Precipitation Reactions When two solutions are mixed and a solid product forms the reaction is known as a precipitation reaction and the solid product is called a precipitate Whether a precipitate forms or does not form depends on the solubility of the products If the product is insoluble it is a precipitate Solubility Guidelines for Ionic Compounds in Water Hydration refers to the dissolution of an ionic compound in water A 1 2 3 4 The solution process in water Polar water molecules surround the positive ions with their negative poles and the negative ions with their positive poles These are called hydrated ions Solubility is defined as the maximum amount of solute that can dissolve in a given amount of solvent at a specified temperature Not all ionic compounds are soluble Solubility depends on the strength of the attractive forces between the ions in the compound and the attraction between the water molecules and the ions Soluble compounds with exceptions 3 Insoluble compounds with exceptions 5 Circle the insoluble compounds MgCl2 Ag2SO4 Ca3 PO4 2 NH4 3PO4 KI Mg OH 2 Ca ClO3 2 NaC2H3O2 PbSO4 Na2CO3 AgNO3 K2CrO4 Types of Chemical Equations Molecular equations include all the substances as they are represented by their chemical formulas AgNO3 aq NaBr aq NaNO3 aq AgBr s In this reaction the reacting species exchange partners to form the products Reactions of this type are referred to as double replacement or metathesis reactions Ionic equations represent the species in the form that they are present in an aqueous solution Ag aq NO3 aq Na aq Br aq Na aq NO3 aq AgBr s Net ionic equations include only the species that have undergone change from reactants to products Ag aq Br aq AgBr s Na aq and NO3 spectator ions aq did not change in the above reaction and are known as Note that in a precipitation reaction the net ionic equation includes only the ions that form the insoluble product Write the balanced net ionic equation for the reaction of Fe NO3 2 aq with Na2CO3 aq B 1 2 3 4 5 4 Review the strong acids and bases on page 2 of the notes III Acid Base Reactions Bronsted definitions A 1 Bronsted acid is a proton donor A proton is a hydrogen ion H HF aq H2O H3O aq F aq acid base 2 Bronsted base is a proton acceptor NH3 aq H2O NH4 base acid aq OH aq 3 Acids are classified as mono di or triprotic depending on the number of protons they contain HCl H2SO4 H3PO4 monoprotic diprotic triprotic Acids with more than one proton are known collectively as polyprotic acids 4 Polyprotic acids ionize in a stepwise manner Each successive ionization occurs to a smaller and smaller extent H3PO4 aq H2O H3O aq H2PO4 aq H2PO4 aq H2O H3O aq HPO4 2 aq HPO4 2 aq H2O H3O aq PO4 3 aq 5 Some bases can provide more than one hydroxide ion and are called dibasic bases H2O Ba OH 2 s Ba2 aq 2 OH aq 5 B 1 2 3 4 1 2 Acid Base Neutralization Neutralization is a reaction in which an acid reacts with a base and forms salt and water HCl aq NaOH aq NaCl aq H2O H2SO4 aq 2 NaOH aq Na2SO4 aq 2 H2O HCl aq NH4OH NH4Cl aq H2O The net ionic equation for any acid base neutralization reaction includes the hydrogen ion from the acid and the hydroxide ion from the base The net reaction in any acid base neutralization is H aq OH aq H2O The cation of the base and the anion of the acid are spectator ions Review questions a b Identify the Bronsted acid and base in the reaction HCl aq NO2 aq HNO2 aq Cl aq Write the molecular and the net ionic equation for the complete neutralization reaction between H3PO4 and KOH IV Oxidation Reduction Reactions A Looking back and looking forward In precipitation reactions the ionic compounds exchange ions to form an insoluble product In neutralization reactions the proton of the acid combines with the hydroxide ion of the base to form water 6 3 4 5 6 B 1 In redox reactions also known as electron transfer reactions one element transfers electrons to another element The element that donates electrons is oxidized in the process and the element that accepts the electrons is reduced Mg s Mg2