Lecture Nine covers the following points:-

- Oxidizing agent
- Potassium Permanganate
- Iodine
- Redox indicator



Potassium Permanganate

• Very strong oxidizing agent Eo=1.51 V
• Self indicator
• Standardized by primary standard sod. Oxalate solution
• 5C2O42- + 2MnO4- + 16H+ =
• 10CO2 + 2Mn2+ + 8H2O
• Determination of ferrous in presence of Cl-
• 2MnO4- + 10 Cl- + 16 H+ =
• 2 Mn2+ + 5 Cl2 + 8 H2O
by using Zimmermann reagent which consists of
• MnSO4 + H2 SO4 + H3PO4

• Mn II: reduce the potential of permanganate
• so it will not oxidize chloride ions
• H3PO4: form a complex with ferric and decrease the potential of iron
•

Iodine

Iodimetry 2 S2O32- + I2 = S4O62- + 2 I-
This titration are usually performed in neutral solution.
In alkaline solution:
I2 + OH- = HIO + I- + H2O
hypoiodite
3 HIO + 3 OH- = IO3- + 2I- + 3 H2O
iodate

consumption of iodine
• In acid solution:
• 1- starch tends to hydrolyze
• so the end point affected.

• 2- reducing power is increased in neutral solution

• 3-iodid produced in the reaction tends to be oxidized

• 4 I- + O2 + 4 H+ = 2 I2 + 2 H2O
• 2 Cu2+ + 2 I- = 2 Cu+ + I2
Iodometry
2 S2O32- + I2 = S4O62- + 2 I-
mmole of Cu2+= mmole of I2 =mmole of S2O32-
• Most iodometric titration are performed in strong acid solution
• To minimize air oxidation of iodide
• Thiosulphate is decomposed in acid solution
• S2O32- + 2H+ = H2SO3 + S
• stirring

Oxidation – Reduction indicators

 Self indicator: permanganate
 Specific indicator : starch
 External indicator: sod. Thiosulphate
 Internal indicator
 They are substances that change color upon being oxidized or reduced