Double Displacement Reactions  + +

Types: Double displacement Example: MgO + CaS S O  Mg Ca + O S Mg Ca + General: AB + CD  AD + CB

Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  product + product AB + CD  AD + CB

Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) Another example: K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s)

For predicting products!

Double Displacement Rxns 2 soluble ionic compounds trade cations (+ve ions) General Equation AB + CD  CB +AD 3 possible products Precipitate Gas Water

4.3 Double Displacement Double Displacement Reactions Continued: This time using the SOLUBILITY TABLE! 3 stipulations must be met for DD to occur or NO RXN.

Will a precipitate form? Precipitate= an insoluble solid If the product is insoluble in water , a precipitate will form (the compound is solid). If the product is soluble in water, no precipitate forms (the compound is aqueous) How do we know which compounds are soluble? Use a solubility table

Rule Exception Nitrates (NO3-) are soluble None Halides (Cl- , Br- , I-) are soluble Ag+, Hg2+, Pb2+ Sulfates (SO42-) are soluble Ca2+, Ba2+, Pb2+, Hg2+, Ag+ Sulfides (S2-) are insoluble NH4+ and ions of groups 1 and 2 Carbonates (CO32-)are insoluble NH4+ and ions of group 1 Phosphates (PO43-)are insoluble Hydroxides (OH-)are insoluble Ca2+, Ba2+, Sr2+, and ions of group 1

Example #1 Aqueous solution of lead(II) nitrate is added an aqueous solution of potassium iodide. Predict the products, balance the chemical equation and predict the solubility of the products. Dissociation = breaking into ions in water Products Pb2+ NO3- K+ I-

Soluble – all nitrates are soluble Example #1: Con’t Skeleton Equation Pb(NO3)2 + KI PbI2 + KNO3 Balanced Equation: Pb(NO3)2 + 2KI PbI2 + 2KNO3 Add states to the equation: Reactants are both aqueous Go to the table Lead (II) iodide Potassium nitrate Insoluble due to lead(II) ion (precipitate forms) Soluble – all nitrates are soluble

Ex #2abc: Determine the products, balance and predict state of the products Silver(I) nitrate (aq) + potassium sulfate (aq)  Li2CO3 (aq) + NaCl (aq) Mercury(II) nitrate(aq) + Lithium bromide(aq) 

Double Displacement Rxns Producing Gases 3 situations where gases are produced: Carbonates react with acids Sulfites react with acids Ammonium salts react with bases In all cases the product containing the carbonate, sulfite or ammonium ion breaks down into H2O and a gas.

Example #3: Carbonate + Acid CaCO3(s) + HCl(aq)  CaCl2(aq) + H2CO3(aq) CO2(g) + H2O(l) The final equation is: CaCO3(s) + HCl(aq)  CaCl2(aq) + CO2(g) + H2O(l) Decomposes

Example #4: Ammonium with Base NH4Cl(aq) + NaOH(aq)  NaCl(aq) + NH4OH(aq) NH3(g) + H2O(l) The final equation is: NH4Cl(aq) + NaOH(aq)  NaCl(aq) + NH3(g) + H2O(l) Decomposes

Example #5: Sulfite with Acid Na2SO3(s) + HCl(aq)  NaCl (aq) + H2SO3 (aq) SO2 (g)+ H2O(l) The final equation is: Na2SO3(s) + HCl(aq)  NaCl (aq) + SO2(g) + H2O(l) Decomposes

How do we know when a gas will form? If one of the products is: H2CO3 (ag)  CO2(g) + H2O(l) H2SO3(aq)  SO2(g) + H2O(l) NH4OH(aq)  NH3(g) + H2O(l) = decomposes into Remember, we still need to show the other product of the double displacement rxn.

Practice: Determine the products, states and balance the equation Na2CO3 (aq) + HBr(aq) 

Ex #6: Neutralization Reactions Double displacement rxn involving an acid and a base as reactants Products are a salt and water Eg. HNO3(aq) + KOH(aq)  KNO3(aq) + H2O(l)

For the following neutralization rxn: Predict the products, states and balance the equation HCl(aq) + NaOH(aq)  H2SO4(aq) + CaOH(aq) 

Wrap-up of Double Displacement Rxns Remember!!! Double displacement rxns only happen when: A precipitate is formed A gas is formed Water is formed In all other cases, the ions stay in solution!!! No rxn happens!!!

Animations for Double Displacement Rxns http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/clm2s3_4.swf http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf

Net Ionic Equations Used when a precipitate is formed in a double displacement rxn. Soluble ionic compounds are present in solution as aqueous ions. disolves in water NaCl(s)  Na+ + Cl- K2SO4(s)  2K+ + SO42-

Why use a Net Ionic Equation It is the ions that will join to create the precipitate, by looking at the ions we get a better idea of what is happening in the solution. Eg. For the reaction: K2CO3 (aq) + BaCl2 (aq)  What are the potential products? Are they soluble?

Total Ionic Equations K2CO3(aq) + BaCl2(aq)  2KCl(aq) + BaCO3(s) KCl  soluble From a BaCO3  insoluble table of solubility We can write the equation using ions for all aqueous compounds Becomes, 2K+ (aq) + CO32- (aq) + Ba2+ (aq) + 2Cl- (aq) 2K+ (aq) + 2Cl- (aq) + BaCO3(s)

From Total  Net Ionic Equations Total ionic equation – contains all ions/compounds 2K+ (aq) + CO32- (aq) + Ba2+ (aq) + 2Cl- (aq) 2K+ (aq) + 2Cl- (aq) + BaCO3(s) The potassium and chloride ions we unchanged by the rxn (in red) Because they do not take part in the rxn, we call them spectator ions If we show only the ions involved in the rxn, we get a net ionic equation

Net Ionic Equations Total ionic equation – contains all ions/compounds 2K+ (aq) + CO32- (aq) + Ba2+ (aq) + 2Cl- (aq) 2K+ (aq) + 2Cl- (aq) + BaCO3(s) Net ionic equation – contains only ions involved in the reaction and the solid they form. For the above reaction the net ionic equation is: CO32- (aq) + Ba2+ (aq)  BaCO3(s)

Down side to the Net Ionic Equation Do not show what aqueous were mixed Ex. CO32- (aq) + Ba2+ (aq)  BaCO3(s) We don’t know which barium compound and which carbonate compound were mixed. We do know that any reaction involving the combination of barium ions and carbonate ions will produce a precipitate! Try one out.

Rules for Net Ionic Equations Solutions of soluble salts (KCl, NaNO3 etc.) All written as ions Solutions of strong acids (HCl, HNO3, H2SO4 and HClO4) Solutions of strong bases (NaOH, KOH, Ba(OH)2) All covalent compounds left in molecular form, states are written beside them. Including all gases, liquids (eg. H2O) and soluble covalent compounds (eg. ethanol)

Steps for Writing a Net Ionic Equation Identify Type of Reaction and Possible Products Look Up Solubility of Both Products Indicate States of Reactants and Products Write Chemical Equation for Reaction Balance Equation Write Total Ionic Equation Write Net Ionic Equation

Ex. Write the total ionic equation and net ionic equation for the reaction of barium sulfide with sodium sulfate.

Practice Predict the products. HCl(aq) + AgNO3(aq)  CaCl2(aq) + Na3PO4(aq)  Pb(NO3)2(aq) + BaCl2(aq)  FeCl3(aq) + NaOH(aq)  H2SO4(aq) + NaOH(aq)  KOH(aq) + CuSO4(aq)  AgCl(aq) + HNO3(aq) Ca3PO4 (aq) + NaCl(aq) PbCl2(aq) + Ba(NO3)2(aq) Fe(OH)3(aq) + NaCl(aq) H2O(aq) + Na2SO4(aq) K2SO4 (aq) + Cu(OH)2(aq)