Lesson 6: Redox Titrations UNIT 7: Lesson 6: Redox Titrations

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

Example When 25.00 mL of a solution with an unknown [Fe2+] is titrated with acidic KMnO4, the titration requires 17.52 mL of acidified 0.1000 M KMnO4. The reaction is: MnO4- + 8 H+ + 5 Fe2+ → Mn2+ + 4 H2O + 5 Fe3+ What is the [Fe2+] in the solution? 10 min

Brain Break! SUMoku!

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

Example A 25.00 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 46.84 mL of 0.7500 M Na2S2O3 to bring the titration to the endpoint according to the equation: 2 S2O32- + I2 → S4O62- + 2 I- What is [OCl-] in the bleach? 10 min

Practice: Pg. 213 #26 and 27 15 min