1. Double Replacement Reactions Cation exchange

2. Driving Force – Two compounds  There must be a driving force for the reaction to take place, otherwise it will remain as a mixture. Driving Forces:  Formation of a precipitate (ppt)  Formation of a gas  Formations of a molecular compound

3. Examples  Formation of a ppt Ag NO 3 + LiBr  Ag + + Br - AgBr  Formation of a gas HCl + K 2 SO 3  H + + SO 3 2- H 2 O + SO 2  Formation of a molecular compound HF + SiO 2  HF + SiO 2 H 2 O + SiF 4

4. Formation of a ppt – net ionic 1. Determine if the reactants are soluble or insoluble. Soluble – separate into ions, insoluble – keep together. 2. Determine the driving force….which combination of species forms a ppt. 3. Write products with precipitates together and solubles as separated. 4. Cross out species that appear exactly the same on both sides of the equation. 5. Write the Balanced Equation with what remains

5. Example  Copper (II) sulfate is added to sodium sulfide CuSO 4 + Na 2 S CuS + Na 2 SO 4 Cu 2+ + SO 4 2- + 2Na + + S 2- CuS + 2Na + + SO 4 2- Net Ionic Equation Cu 2+ + S 2- CuS