2. Double- Replacement Reactions Emily Pregartner Iman Williams

3. What is a double replacement reaction?  A double replacement reaction is a chemical reaction where two reactant ionic compounds exchange ions to form two new product compounds with the same ions.

4. o In a balanced equation you should have the same number of atoms of each element on both sides of the equation. o As stated in the Law of Conservation of Mass “Matter is neither created or destroyed”  This means that you didn’t gain or lose atoms during the reaction, they might be combined differently but they are still there To understand double replacement reactions you need to know the basics of balancing equations

5. How to Write a Double Replacement Reaction o When writing your formulas swap the inside elements and join them with their new partners X + Y  Y + X Remember after writing the correct formulas you still have to balance the equation!!!

6. Writing the Equation CaBr 2 + AgNO 3 → Ca(NO 3 ) 2 + AgBr Balanced Equation: CaBr 2 + 2AgNO 3 → Ca(NO 3 ) 2 + 2AgBr

7. For a Double replacement reaction to occur one of the following must be true: o One product is only slightly soluble (can be dissolved) and precipitates from solution leaving the other product dissolved in solution. Na 2 S(aq) + Cd(NO 3 ) 2 (aq)  CdS(s) + 2NaNO 3 (aq) o One product is a gas that bubbles out of the mixture. 2NaCN(aq) + H 2 SO 4 (aq)  2HCN(g)+ Na 2 SO 4 (aq) o One product is a molecular compound such as water, which separates from the ions in solution as intact molecules. Ca(OH) 2 (aq) + 2HCl(aq)  CaCl 2 (aq)+2H 2 O(l)

8. Example Problem Ag 2 SO 4 (aq) +AlCl 3 (aq)  Ag 2 SO 4 (aq) +AlCl 3 (aq)  AgCl + Al 2 (SO 4 ) 3 Ag 2 SO 4 (aq) +2AlCl 3 (aq)  AgCl + Al 2 (SO 4 ) 3 Ag 2 SO 4 (aq) +2AlCl 3 (aq)  6AgCl + Al 2 (SO 4 ) 3 3Ag 2 SO 4 (aq) +2AlCl 3 (aq)  6AgCl + Al 2 (SO 4 ) 3

9. Try these on your own! 1.) Which of the following equations is balanced correctly and has the right products for the reactants Na 3 PO 4 + KOH -> a.Na 3 PO 4 + 3KOH -> 3NaOH + K 3 PO 4Na 3 PO 4 + 3KOH -> 3NaOH + K 3 PO 4 b.Na 3 PO 4 + KOH -> NaOH + K 3 PO 4Na 3 PO 4 + KOH -> NaOH + K 3 PO 4 c.NaPO 4 + KOH -> 2NaOH + K 3 PONaPO 4 + KOH -> 2NaOH + K 3 PO 2.) Which of the following equations is balanced correctly and has the right products for the reactants? MgCl2 + Li2CO3 -> a. MgCl 2 + Li 2 CO ->MgCO + 2LiClMgCl 2 + Li 2 CO ->MgCO + 2LiCl b. MgCl 2 + Li 2 CO 3 -> MgCO 3 + 2LiClMgCl 2 + Li 2 CO 3 -> MgCO 3 + 2LiCl

10. Links That Can Help You  http://sartep.com/chem/tutorials/tut.cfm ?tutorial=Double+Replacement+Reaction s&chap=6 http://sartep.com/chem/tutorials/tut.cfm ?tutorial=Double+Replacement+Reaction s&chap=6  http://www.chemteam.info/Equations/Do ubleReplacement.html http://www.chemteam.info/Equations/Do ubleReplacement.html  http://chemistry.about.com/cs/stoichiom etry/a/aa042903a.htm http://chemistry.about.com/cs/stoichiom etry/a/aa042903a.htm

11. Homework Question  Write the correct formulas for H 3 PO 4 + NaBr -> then balance the equation.