2A closer look at Double Replacement Reactions Instead of FIGHTING (Single Replacement)Double Rep. Are all about LOVEEvidence of the DR is either:A precipitate formingan acid/base (two ionic) reaction forming covalent water moleculesneutralizationIf neither happens, No Reaction4/1/2017
3Aqueous SolutionsMany times, the chemicals we are reacting together are dissolved in water.Mixtures of a chemical dissolved in water are called aqueous solutions.The chemicals must first be dissolved in waterCompounds separate into free ions.
4When some ionic compounds dissolve in water, The anions and cations are separated from each other. DissociationBecause they are more attracted to polar water molecules.NaCl(s) Na+(aq) +Cl- (aq)Ions are FREE to movethroughout the solution.4/1/2017
5When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion.AgNO3 (s) Ag+ (aq) + NO3-(aq)
6Dissociation, Continued Sodium chloride dissociates in waterNaCl(s) → Na+1(aq) + Cl-1(aq)Silver nitrate dissociates in waterAgNO3(s) → Ag+1(aq) + NO3-1(aq)Na+1Cl-1NaClNO3NO3-1AgAg+1
7A cation and anion combine to form an insoluble precipitate. DR ReactionsOccurs ifA cation and anion combine to form an insoluble precipitate.If no precipitate forms, then NR (no reaction).
8Why did a precipitate form? Ions in AgCl are more attracted to each other than to the polar water molecules.Fall madly deeply in love, wrap their arms around each other, and drop out of the solution as a solid.AgCl(s)
9What about the other couple, NaNO3? The ions of NaNO3 are more attracted to the polar water molecules and stay separate (dissociated)Soluble product is shown as (aq)Na+ (aq) + NO3- (aq)4/1/2017
10So, how do you know if a new product is (s) or (aq)? Gross equation:NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)Net equation:Cl- (aq) + Ag+ (aq) AgCl (s)So, how do you know if a new product is (s) or (aq)?Solubility Rules4/1/2017
11Solubility of Ionic Salts General Rules1. Sodium (Na+1), potassium (K+1), and ammonium (NH4+1)compounds are soluble in water.2. Nitrates (NO3-1), acetates (C2H3O2-1), and chlorates (ClO3-1)are soluble.3. Chlorides (Cl-1) are soluble except with silver (Ag+1),mercury(I) (Hg2+2), and lead(II) (Pb+2).[Lead(II) chloride is soluble in hot water.]4. Sulfates (SO4-2) are soluble except with calcium (Ca+2),barium (Ba+2), strontium (Sr+2), and lead(II) (Pb+2).5. Carbonates (CO3-2), phosphates(PO4-3), andsilicates (SiO3-2) are insoluble except with sodium (Na+1),potassium (K+1), and ammonium (NH4+1).6. Sulfides (S-2) are insoluble except with calcium (Ca+2),barium (Ba+2), strontium (Sr+2), magnesium (Mg+2),sodium (Na+1), potassium (K+1), andammonium (NH4+1).4/1/2017
13Determine whether each of the salts is soluble or insoluble: AgBrCaCl2Pb(NO3)2PbSO4CuSFe2(SO4 )3PbCO3NH4ClAgBr insolubleCaCl2 solublePb(NO3)2 solublePbSO4 insolubleCuS insolubleFe2(SO4 )3 solublePbCO3 insolubleNH4Cl soluble4/1/2017
17No Precipitate Formation = No Reaction KI(aq) + NaCl(aq) KCl(aq) + NaI(aq)All ions still present, no reaction.
18Process for Predicting the Products of a Precipitation Reaction Write the formula for the reactants.Exchange ions. (Trade dance partners)(+) ion combines with (-) ionCriss-cross ionic charges of new dance couples to get formulas. (Don’t worry about balancing the equation yet.)Use the solubility rules to determine solubility of each product in water.If product is insoluble or slightly soluble, it will precipitate. Write (s) behind it.If the product is soluble, write (aq) behind it.If neither product will precipitate, no reaction.5. Eliminate the spectator ions (those that are (aq) on both sides)6. Write a balanced net ionic equation.
19Write the formulas of the reactants Exchange the ions. An aqueous Solution of Sodium Carbonate Is Added to an Aqueous Solution of Copper(II) Chloride, a White Solid Forms.Write the formulas of the reactantsNa2CO3(aq) + CuCl2(aq) Exchange the ions.Na2CO3 (aq) + CuCl2 (aq) Na+ + Cl- + Cu2+ + CO32-3. Criss-Cross charges and reduceNa2CO3(aq) + CuCl2(aq) NaCl + CuCO3
204. Determine solubility of products NaCl is solubleCuCO3 is insoluble.Na2CO3(aq) + CuCl2(aq) 2 NaCl(aq) + CuCO3(s)5. Na+ and Cl- are (aq) on both sides. Spectators. Eliminate.Net ionic equation:CO32-(aq) + Cu2+(aq) CuCO3(s)4/1/2017
21Consider: AlCl3(aq) + AgNO3(aq) Write the dissociation equation of each reactant:AlCl3(s) Al+3(aq) + 3 Cl-1(aq)Why 3 Cl-1(aq) and NOT Cl3-1 ?AgNO3(s) Ag+1(aq) + NO3-1(aq)4/1/2017
22One of two things can happen: All ions remain “free”No reaction happens.Two oppositely charged ions are attracted to each other strongly, bondForm a precipitate.4/1/2017
23What are the products (possible new dance couples? Al+3 combines with NO3- : Al(NO3)3Ag+1 combines with Cl-1 : AgClWhy NOT AlAg? Or NO3Cl ?Does one, both, or neither product form a precipitate?4/1/2017
29FeBr2(aq) + AgNO3(aq) Dissociation of reactants? Fe+2(aq) + 2 Br –1(aq) + Ag+1(aq) + NO3 -1(aq)New Dance Couples?Fe (NO3)2 and AgBrCheck table for precipitateFe(NO3)2 is soluble or (aq)AgBr is insoluble or (s)4/1/2017