1. Matt Berlin Balancing Half Reactions and Predicting Single Replacement Reactions

3. A half reaction does not occur by itself

4. At least two such reactions must be coupled for a Redox Reaction

5. Here are some examples of a half reaction2H+ + 2e-  H2 Cu  Cu2+ + 2e- Cl2 + 2e-  2Cl- What is a Half Reaction

7. When an element gains an electron it is reduction

8. Remember the acronym O.i.l.r.i.g.Oxidation is loss Reduction is Gain What is Oxidized and What is Reduced?

9. Steps to Balance A Half-Reaction Identify key element that undergoes an oxidation state change Balance the number of atoms for the key element Add electrons to compensate for oxidation state change Add H+ or OH- to balance charge Add H2O as needed to balance equation

10. Example Of Balancing a Half-Reaction Balance the two half reactions for the reaction in an acid solution H2O2 + I  I2 + H2O First Identify what is being oxidized/reduced The Half-reaction 2I-  I2 Shows Oxidation The Half-reaction H2O2  2H2O

11. Example Cont. Add Electrons to compensate for the changes in oxidation state For the Iodine reaction you must add two electrons to the products 2I- I2 + 2e- For the Oxygen reaction you must add two electrons to the reactants H2O2 + 2e- 2H2O

12. Example Cont. Add H+ or OH- to balance the charge In this case H+ should be added to the reduction half reaction, the balanced equations are as follows 2I- I2 + 2e- (oxidation) H2O2 + H+ + 2e-  2H2O (reduction)

14. Remember O.i.l.r.i.g.Oxidation is loss Reduction is gain

16. The more active metal replaces the less active metal

19. Steps for Doing a Single Replacement Reaction Figure out if the reaction will occur by using the activity series Write reactions Write products Balance

20. Example of a Single Replacement Reaction Magnesium Metal + Aqueous Aluminum Chloride Figure out if the reaction will occur by looking at the activity series Magnesium is higher on the activity series than aluminum Thus the reaction will occur Amy, “Beakers” January 28, 2010 via Flickr, Creative Commons Attribution.

22. Aluminum Chloride would be come AlCl3The reactants would look as follows: Mg + AlCl3

23. Example Cont. Carry out the single replacement and write the products Magnesium would replace aluminum in the reaction as follows Mg + AlCl3 MgCl2 + Al Al has a 1- charge and Mg has a 2+ charge so they combine to make MgCl2

24. Example Cont. Balance the Equation The Cl’s in the equation are not balance The least common multiple is 6 for the Cl’s Multiply the AlCl3 by 2 and MgCl2 by 3 Now the Cl’s are balanced and the equations looks like this: Mg + 2 AlCl3  3 MgCl2 + Al

25. Example Cont. Balance the equation The Al’s and the Mg’s are now unbalanced Multiply the Mg by 2 and the Al by 3 as follows 3Mg + 2AlCl3  3MgCl2 + 2Al This is the final equation