1. Lesson 6: Redox Titrations
UNIT 7:
Lesson 6: Redox Titrations

2. A Useful Oxidizing Agent
When you wish to determine the concentration of a reducing agent, a useful substance for titrating is the permanganate ion, MnO4-.
MnO4- is an extremely strong oxidizing agent and can thus oxidize many substances.
MnO4- is purple in solution, but it is reduced to form Mn2+, which is colourless.
10 min

3. Example
When mL of a solution with an unknown [Fe2+] is titrated with acidic KMnO4, the titration requires mL of acidified M KMnO4. The reaction is:
MnO H+ + 5 Fe2+ → Mn H2O + 5 Fe3+
What is the [Fe2+] in the solution?
10 min

4. Brain Break!
SUMoku!

5. A Useful Reducing Agent
To determine the concentration of an oxidizing agent, the iodide ion, I-, is often used.
First, the I- is oxidized to I2 by the unknown substance. An excess of I- is used since the amount of I2 produced is what matters.
Next, the solution containing I2 is titrated with the reducing agent Na2S2O3.
Starch is used as an indicator, since starch and I2 react to produce a blue colour, which disappears once the I2 is oxidized to I-.
10 min

6. Example
A mL sample of bleach (NaOCl) is reacted with excess KI according to the reaction:
2 H+ + OCl- + 2 I- → Cl- + H2O + I2
The I2 produced requires exactly mL of M Na2S2O3 to bring the titration to the endpoint according to the equation:
2 S2O32- + I2 → S4O I-
What is [OCl-] in the bleach?
10 min

7. Practice:
Pg. 213 #26 and 27
15 min