Worksheet #3

Chem 1B Worksheet #2 Name ____________ Due 1/11/13 (1/6/13 stamp)

I. Balance Redox Equations in acid (H+) or basic (OH-) media. Assume ions are (aq), even when “aq’ is not shown.

1. MnO4- + Sn2+ ( Mn2+- + Sn4+ H+

2. FeCl2 + H2O2 ( FeCl3 + H2O H+

3. AsO43- + I- ( AsO33- + I2 H+

4. I2(s) + S2O32- ( I- + S4O62-

5. NO3- + I- ( NO(g) + I2(s) H+

6. Cr2O72- + NH4Cl ( Cr3+ + N2(g) H+

7. PbO(s) + NH3 ( N2(g) + H2O(l) + Pb(s) OH-

8. CrO42- + Fe2+ ( Cr3+ + Fe3+ OH-

9. CrO2- + ClO- ( Cl-+ CrO42- OH-

10. MnO4- + H2C2O4 ( CO2 + MnO2 OH

11. CrO2- + HO2- ( CrO42- OH-

12. Cl2 ( ClO3- + Cl- OH-

II. Balance equations page 177, 4.121 (a) to (f) total 6 assignments

Steps to balance a redox equation:

1. Recognize the reaction is a re-dox process – there is oxidation # changes with specific elements. Oxidation# increases = oxidation; Oxidation # decreases = reduction. Oxidation and reduction always happen within the same reaction.

2. Separate into 2 half-reactions. One show oxidation and the other reduction.

3. Balance the half equations for mass – only for the key elements at this time.

4. Balance the half equations for charge – adding e’s. * Find change of the oxidation number of a specific element and decide how many e’s to add