Double Replacement Rxn Chemistry I

A closer look at Double Replacement Reactions Instead of FIGHTING (Single Replacement) Double Rep. Are all about LOVE Evidence of the DR is either: A precipitate forming an acid/base (two ionic) reaction forming covalent water molecules neutralization If neither happens, No Reaction 4/1/2017

Aqueous Solutions Many 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 water Compounds separate into free ions.

When some ionic compounds dissolve in water, The anions and cations are separated from each other. Dissociation Because they are more attracted to polar water molecules. NaCl(s)  Na+(aq) +Cl- (aq) Ions are FREE to move throughout the solution. 4/1/2017

When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion. AgNO3 (s)  Ag+ (aq) + NO3-(aq)

Dissociation, Continued Sodium chloride dissociates in water NaCl(s) → Na+1(aq) + Cl-1(aq) Silver nitrate dissociates in water AgNO3(s) → Ag+1(aq) + NO3-1(aq) Na+1 Cl-1 Na Cl NO3 NO3-1 Ag Ag+1

A cation and anion combine to form an insoluble precipitate. DR Reactions Occurs if A cation and anion combine to form an insoluble precipitate. If no precipitate forms, then NR (no reaction).

Why 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)

What 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

So, 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 Rules 4/1/2017

Solubility of Ionic Salts General Rules   1.    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), and silicates (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), and ammonium (NH4+1). 4/1/2017

Solubility Patterns… Generally Soluble Generally Insoluble Cations: NH4+, Li+, Na+, K+ Ag+, Pb2+, Hg2+ Anions: Cl-, Br-, I-, NO3-, ClO3-, C2H3O2- OH-, S2-, CO32-, PO43-, CrO42-

Determine whether each of the salts is soluble or insoluble: AgBr CaCl2 Pb(NO3)2 PbSO4 CuS Fe2(SO4 )3 PbCO3 NH4Cl AgBr insoluble CaCl2 soluble Pb(NO3)2 soluble PbSO4 insoluble CuS insoluble Fe2(SO4 )3 soluble PbCO3 insoluble NH4Cl soluble 4/1/2017

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Precipitation Reactions, Continued 2 KI(aq) + Pb(NO3)2(aq)  2 KNO3(aq) + PbI2(s)

DR Precipitation Reaction 2 KI(aq) + Pb(NO3)2(aq)  2 KNO3(aq) + PbI2(s)

No Precipitate Formation = No Reaction KI(aq) + NaCl(aq)  KCl(aq) + NaI(aq) All ions still present,  no reaction.

Process for Predicting the Products of a Precipitation Reaction Write the formula for the reactants. Exchange ions. (Trade dance partners) (+) ion combines with (-) ion Criss-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.

Write 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 reactants Na2CO3(aq) + CuCl2(aq)  Exchange the ions. Na2CO3 (aq) + CuCl2 (aq)  Na+ + Cl- + Cu2+ + CO32- 3. Criss-Cross charges and reduce Na2CO3(aq) + CuCl2(aq)  NaCl + CuCO3

4. Determine solubility of products NaCl is soluble CuCO3 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

Consider: 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

One of two things can happen: All ions remain “free” No reaction happens. Two oppositely charged ions are attracted to each other strongly, bond Form a precipitate. 4/1/2017

What are the products (possible new dance couples? Al+3 combines with NO3- : Al(NO3)3 Ag+1 combines with Cl-1 : AgCl Why NOT AlAg? Or NO3Cl ? Does one, both, or neither product form a precipitate? 4/1/2017

AgCl insoluble Al(NO3)3 soluble AgCl (s) Al+3(aq) + 3NO3-1 (aq) 4/1/2017

Gross and Net Equations Al+3 (aq) + 3 Cl-1(aq) + 3Ag+1(aq) + 3NO3-1(aq) 3 AgCl (s) + Al+3 (aq) +3 NO3- (aq) Eliminate spectators. Net Ionic equation: Ag+(aq) + Cl_ (aq)  AgCl (s) 4/1/2017

Pb(NO3)2 (aq) + KI (aq)  Write the dissociation equations for each salt. Pb+2(aq) + NO3-(aq) + K+ (aq) + I-(aq) Determine what the products are. PbI2 and KNO3 4/1/2017

Pb(NO3)2 (aq) + KI (aq)  Which is the precipitate? Gross Equation: PbI2 is insoluble (forms a precipitate) Gross Equation: Pb+2(aq) + NO3-(aq) + K+ (aq) + I-(aq)  PbI2 (s) + KNO3 (aq) Net Ionic Equation: Pb2+ (aq) + 2 I-(aq)  PbI2 (s) 4/1/2017

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FeBr2(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 AgBr Check table for precipitate Fe(NO3)2 is soluble or (aq) AgBr is insoluble or (s) 4/1/2017

Ag+1(aq) + Br-1(aq)  2AgBr (s) Fe+2(aq) + 2 Br –1(aq) + Ag+1(aq) + NO3 -1(aq) Fe+2(aq) + NO3 -1(aq) + AgBr (s) Net ionic Equation: Ag+1(aq) + Br-1(aq)  2AgBr (s) 4/1/2017