5 Questions
What is the purpose of adding HCO3- to the reaction?
To remove H+ ions and lower the potential of AsO43-/AsO33- system
What is the effect of excess I2 on the Fe3+/Fe2+ system?
It lowers the oxidation potential of I2/I- system to facilitate the quantitative oxidation of I- into iodine
What is the expected role of Cu2+ salts based on their oxidation potential?
To liberate iodine from iodides
What would facilitate the backward reaction for the AsO43-/AsO33- system?
Increased H+ ions
What is the role of adding F- or phosphate to the I2/2I- system?
To lower the oxidation potential of I2/2I- system by forming complexes with Fe3+
Study Notes
Standard Oxidation Potentials of I2/I- System
- The standard oxidation potential of I2/I- system has a relatively low value of +0.54 V at 25°C.
Reducing Agents Oxidized with Free Iodine
- Reducing agents with E0 < +0.54 V can be oxidized with free iodine.
- Examples of such reducing agents include:
- Sn4+/Sn2+ (E0 = +0.15 V)
- S4O62-/S2O32- (E0 = -0.08 V)
- S/S2- (E0 = -0.55 V)
Reactions of Reducing Agents with Free Iodine
- Sn2+ + I2 → Sn4+ + 2I
- S2O32- + I2 → S4O62- + 2I
- S2- + I2 → S + 2I
Oxidizing Agents Reduced by Iodide Ions
- Oxidizing agents with E0 > +0.54 V can be reduced by iodide ions.
- Examples of such oxidizing agents include:
- MnO4- / Mn2+ (E0 = +1.52 V)
- ClO3- / Cl- (E0 = +1.45 V)
- Cr2O72- / Cr3+ (E0 = +1.3 V)
Reactions of Oxidizing Agents with Iodide Ions
- MnO4- + 10 I- + 16 H+ → Mn2+ + 5I2 + 8 H2O
- ClO3- + 6 I- + 6 H+ → Cl- + 3I2 + 3 H2O
- Cr2O72- + 6 I- + 14 H+ → 2Cr3+ + 3I2 + 7 H2O
Systems with Oxidation Potentials Near to I2/I- System
- AsO43-/AsO33- (E0 = +0.55 V) has an oxidation potential near to that of the I2/I- system.
Test your knowledge of the I2/I- system and standard oxidation potentials at 25°C with this quiz. Learn about the basis of iodimetric methods of analysis and iodometric methods of analysis, including reducing agents and oxidizing agents.
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