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Learn difference between Iodometric and Iodimetric titration with case studies and FAQs
What Is Difference Between Iodometric And Iodimetric Titration?
In Iodometric titration, the titrant is iodine (I₂), which is produced locally by reaction with iodide (I⁻) ions of the sample, whereas in Iodimetric titration, the titrant is the iodine solution itself, which is titrated directly against the analyte.
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Iodometric Titration
Definition: In iodometric titration, the titrant is iodine (I₂) generated in situ by the reaction of a sample with iodide (I⁻) ions.
Process: The analyte (substance being analysed) is oxidising in nature and reacts with iodide ions to liberate iodine.
The liberated iodine is then titrated with a standard solution of a reducing agent, typically sodium thiosulfate (Na₂S₂O₃).
Key point: Iodine is produced during the reaction and then titrated.
Example: Estimation of copper(II) ions – Cu²⁺ oxidises iodide ions to iodine, which is then titrated with thiosulfate.
Iodimetric Titration
Definition: In iodimetric titration, the titrant is iodine solution itself, which is directly titrated against the analyte.
Process: The analyte is reducing in nature and reacts directly with the iodine solution.
After the reaction, excess iodine is usually titrated with sodium thiosulfate.
Key point: Iodine is added directly as a titrant.
Example: Estimation of ascorbic acid (vitamin C), which reduces iodine.
Difference Between Iodometric And Iodimetric Titration
Feature
Iodometric Titration
Iodimetric Titration
Type
Indirect
Direct
Iodine Role
Produced in reaction
Used as titrant
Titrant
Sodium thiosulfate
Iodine solution
Used to Analyse
Oxidizing agents
Reducing agents
Example Reaction
Cu²⁺ + I⁻ → CuI + I₂ → titrated
SO₂ + I₂ → H₂SO₄ + HI
Case Study: Iodometric Titration
Study: Determination of Copper(II) Content in Brass Using Iodometric Titration
Principle: Copper(II) ions (Cu²⁺) in the brass sample oxidise iodide (I⁻) to iodine (I₂). The liberated iodine is then titrated with sodium thiosulfate.
2Cu2++ 4I– = 2CuI (s) + I2
I2 + 2S2O32- = 2I– + S4O62-
Procedure:
Dissolve the brass in nitric acid to free Cu²⁺.
Add potassium iodide (KI) to generate iodine.
Titrate the liberated iodine with standard Na₂S₂O₃.
Use starch as an indicator near the endpoint.
Note:
The amount of sodium thiosulfate used corresponds to the iodine liberated, which in turn reflects the copper content. Results give the % Cu in brass.
Case Study: Iodimetric Titration
Objective: To determine the amount of vitamin C (ascorbic acid) in commercial fruit juice samples.
Principle: Ascorbic acid is a reducing agent. It reduces iodine to iodide, and itself gets oxidized to dehydroascorbic acid. Iodine is directly titrated into the juice until all ascorbic acid is consumed.
C6H8O6 + I2 = C6H6O6 + 2HI
Procedure:
Dilute the juice sample and acidify it.
Titrate with standard iodine solution.
Use starch as an indicator (blue colour appears at the endpoint when excess iodine is present).
Note:
The volume of iodine used is directly proportional to the amount of vitamin C. The Final result is given as mg of ascorbic acid per 100 mL of juice.
Why is starch used as an indicator in both iodometric and iodimetric titrations?
Starch forms a deep blue complex with free iodine (I₂), making it highly sensitive and visible even at very low iodine concentrations. It helps detect the endpoint of the titration—when iodine is just about to disappear (in iodometry) or when excess iodine appears (in iodimetry)
Why is sodium thiosulfate commonly used in iodometric titrations?
Sodium thiosulfate is a strong and reliable reducing agent that reacts precisely with iodine to form iodide. It’s stable, easy to handle, and gives accurate, sharp endpoints with starch, making it ideal for iodometric titrations.
Can iodometric and iodimetric titrations be used interchangeably?
No, they cannot.
Iodometric titration is used to determine oxidising agents by measuring the iodine they generate.
Iodimetric titration is used to determine reducing agents by titrating them directly with iodine.
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