1. Ammonium Dichromate Volcano! 1)When heated, ammonium dichromate decomposes to produce a chromium oxide compound, a gas, and water vapor. Write and balance this reaction. 2) Balance each of these reactions: S + HNO 3  H 2 SO 4 + NO 2 + H 2 O NH 3 + CuO  Cu + N 2 + H 2 O

2. Take out your Oxidation Numbers Handout and your Balancing Redox Reactions lecture notes and skim through both of them…. Solve for y and z using elimination: y + z = 42z + y = 12 (-2)(y + z = 4) -2y -2z = -8 2z + y = 12 -y = 4 so y = -4 z = 8

3. Redox Reactions Oxidation-Reduction (Redox) Reaction: reaction in which 1 or more e- is transferred

4. LeO says GeR Losing electrons is oxidation Gaining electrons is reduction Oxidation Number: the charge an atom would have if the shared electrons were assigned to the more electronegative atom

5. 1. Assign oxidation numbers to each element in the equation. Then identify the oxidizer and reducer in the reaction. Zn(s) + 2H + (aq) → Zn 2+ (aq) + H 2 (g) 0+1+2 0 Oxidizer: HReducer: Zn Zn reduced the charge of H from +1 to 0 by giving e- to H. As a result, Zn got oxidized by H, and it’s charge went from +1 to +2.

6. 2. Assign oxidation numbers to each element in the equation below. Then identify the oxidizer and reducer in the reaction 2PbS(s) + 3O 2 (g) → 2PbO(s) + 2SO 2 (g) + 2 -2 0 + 2 -2 +4 (each O = -2, so -4) O’s oxi # went from 0 to -2: oxi # was reduced by S S went from -2 to +4: got oxidized by O O = oxidizerS = reducer

7. 3. Liquid iodine reacts with a sodium bromide solution. Write the equation, figure out the oxidation number of each species, identify the oxidizer and reducer, and separate the reaction into two HALF reactions. We will balance the equation together. iodine = oxidizer 0 -1 -1 0 bromine = reducer I 2 (l) + Br - (aq)  I - + Br 2 (l) I 2  I - Br -  Br 2 I 2 (l) + 2Br - (aq)  2I - + Br 2 (l) This is easy to balance, but what if I asked you to balance: Fe 2+ (aq) + MnO 4 - (aq) → Fe 3+ + Mn 2+ (aq) Water is not always shown but is a common reactant in redox. Those oxygens came from somewhere. Also, equations have to be balanced in terms of charge as well as number of atoms. 22+ 2e2e +

8. Balancing Redox Reaction Equations 4. Balance the following reaction in acid: Fe 2+ (aq) + MnO 4 - (aq) → Fe 3+ + Mn 2+ (aq) Steps 1.Assign each species an oxidation number to determine the oxidizer and reducer. This will help you break the reaction into 2 half reactions: one reduction, one oxidation Fe 2+ (aq) → Fe 3+ (aq) MnO 4 - (aq) → Mn 2+ (aq) 2+ 3++7 -82+ Lost e- (oxidized)Gained -e (reduced)

9. Differs depending on if the reaction takes place in an acidic or basic solution IN ACID ii. Balance non H & O atoms iii. Add H 2 O to balance O iv. Add H + to balance H v. Add electrons to make each side of the equation have the same net charge MnO 4 - (aq) → Mn 2+ (aq) + 4H 2 O8H + + 5e- + Fe 2+ (aq) → Fe 3+ (aq) + 1e-

10. 6. Add together the two half reactions so the electrons cancel algebraically 5e- + 8H + + MnO 4 - (aq) → Mn 2+ (aq) + 4H 2 O Fe 2+ (aq) → Fe 3+ (aq) + 1e- 5Fe 2+ (aq) → 5Fe 3+ (aq) + 5e- 8H + (aq) + 5Fe 2+ (aq) + MnO 4 - (aq) → 5Fe 3+ (aq) + Mn 2+ (aq) + 4H 2 O 7. Cancel other species and check to make sure the equation is balanced X 5

11. 5. Balance this redox reaction (in acid) using the half-reaction method: Cr 2 O 7 2- + Cl -  Cr 3+ + Cl 2 Cl -  Cl 2 Cr 2 O 7 2-  Cr 3+ 2 2 + 2e - + 7H 2 O14H + + ) 3( 6Cl -  3Cl 2 + 6e - 6e - + 14H + + 6Cl - + Cr 2 O 7 2-  2Cr 3+ + 7H 2 O + 3Cl 2

12. 6. Balance the following reaction which occurs in base: Al (s) + NO 2 - (aq) → NH 3 (g) + AlO 2 - (aq) Al (s) → AlO 2 - (aq) 8OH - + 4H 2 O + 2Al (s) → 2AlO 2 - (aq) + 8H 2 O + 6e - 8OH - + 2Al (s) → 2AlO 2 - (aq) + 4H 2 O + 6e - In base: then, add same number of OH - as H + you put in to both sides of equation. On one side, OH - combine with H + to make H 2 O, and cancel with some H 2 O on other side. Check if balanced. NO 2 - (aq) → NH 3 (g) 6e - + 5H 2 O + NO 2 - (aq) → NH 3 (g) + 7OH - + 2H 2 O ++ 4H + + 4OH - 4OH - + 7H + +7OH - + 2H 2 O +7OH - + 3e- 6e- + H 2 O (l)+OH - (aq)+ NO 2 - (aq) + 2Al (s) → 2AlO 2 - (aq) + NH 3 (g)

13. Balance each of these reactions: 1S + 6HNO 3  1H 2 SO 4 + 6NO 2 + 2H 2 O 2NH 3 + 3CuO  3Cu + 1N 2 + 3H 2 O

14. Ammonium Dichromate Volcano! When heated, ammonium dichromate decomposes to produce a chromium oxide compound, a gas, and water vapor. Write and balance this reaction. What DO I know? (NH 4 ) 2 Cr 2 O 7 (s)  H 2 O(g) + Cr?O?(s) + gas with N (NH 4 ) 2 Cr 2 O 7 (s)  4H 2 O(g) + Cr 2 O 3 (s) + N 2 (g)

15. Start on your Redox HW… USE YOUR TIME WISELY