1. Lecture 29 11/11/05

2. Winkler method to measure O2
2Mn2+(aq) + 4OH-(aq) + O2(aq)  2MnO2 (s) + 2H2O
MnO2(s) + 3I-(aq) +4H3O+(aq)  Mn2+(aq) + I3-(aq) + 6H2O
I3-(aq) + 2S2O32-  3I-(aq) + S4O62-

3. Using the Winkler Method (equations below), find the mg/L of O2 (FM=32g/mol), if 10 mL of 0.1 M Na2S2O3 was needed to titrate a 1 L sample.
2Mn2+(aq) + 4OH-(aq) + O2(aq)  2MnO2 (s) + 2H2O
MnO2(s) + 3I-(aq) +4H3O+(aq)  Mn2+(aq) + I3-(aq) + 6H2O
I3-(aq) + 2S2O32-  3I-(aq) + S4O62-

4. 12-47
A g sample of window cleaner containing ammonia was diluted with g of water. Then g of solution were titrated with mL of M HCl to reach a bromocresol green end point. Find the weight percentage of NH3 (FM ) in the cleaner.

5. 16-25
A g portion of a copper(II) salt was dissolved in a 250-mL volumetric flask. A 50.0-mL aliquot was analyzed by adding 1 g of KI and titrating the liberated iodine with mL of M Na2S2O3. Wt% of copper in salt?
Copper = 63.5 g/mol

6. 14-22

7. 2Cu2+ + 5I-  2CuI(s) +I3-
e- + Cu2+ + I-  CuI(s)
3I-  I3- + 2e-