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.

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.

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Difference Between Iodometric And Iodimetric Titration

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 + 2S₂O₃^2- = 2I^– + S₄O₆^2-

Procedure:

1. Dissolve the brass in nitric acid to free Cu²⁺.
2. Add potassium iodide (KI) to generate iodine.
3. Titrate the liberated iodine with standard Na₂S₂O₃.
4. 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:

1. Dilute the juice sample and acidify it.
2. Titrate with standard iodine solution.
3. 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.

Related:

• Relative Response Factor (RRF) in Pharmaceutical Analysis

FAQs

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.

Further Reading

• Top Interview Questions On Titration And Their Answer