Titrimetric Methods Involving Oxidation-Reduction Reactions

Understanding Titrimetric Methods Involving Oxidation-Reduction Reactions

  • Titration is a common method used in chemistry to figure out an unknown concentration in a solution, or to measure the reacting volumes of solutions.
  • Oxidation-reduction titrations, also known as redox titrations, are a type of titration that uses a redox reaction to determine the concentration of an unknown analyte.
  • The redox reaction involves a transfer of electrons from one species to another. This reduction or oxidation is what’s measured in a titrimetric redox reaction.

Steps in a Redox Titration

  • A redox titration usually involves the addition of a known concentration of oxidising or reducing agent (the titrant) to an unknown concentration of the other in a carefully measured volume.
  • As the titrant is added to the analyte solution, the amount of the reducing or oxidising agent in the solution either decreases or increases - this change allows the endpoint of the titration to be determined.
  • A suitable indicator is chosen that changes colour at (or near) the equivalence point – the point where stoichiometrically equal quantities of the reagents have reacted.

Types of Redox Titrations

  • Permanganate titrations use KMnO4, a strong oxidising agent, commonly with acidic solutions to ensure a clear change of colour (from purple) at the end point.
  • Dichromate titrations also involve a strong oxidising agent (K2Cr2O7), which is used with acidic solutions. The colour change involved goes from orange (chromium VI) to green (chromium III).
  • Iodometric titrations also referred to as iodometry, where iodine (I2) reacts with an oxidising agent in the solution, forming iodide (I-). The end point is detected by the sudden disappearance of the blue colour of the starch-iodine complex.

Applications of Redox Titrations

  • Redox titrations are particularly useful in the detection and analysis of chemical oxygen demand (COD) in environmental samples, for example, to determine the amount of pollutants in bodies of water.
  • It’s also used extensively in the **pharmaceutical industry to establish the level of active ingredients in a product or the level of impurities.
  • Redox titrations can be applied to analyse certain vitamins like ascorbic acid (vitamin C) and riboflavin (vitamin B2), where they act as reducing agents.

Precautions in Redox Titrations

  • Accuracy is critical in titrations, so always ensure to measure volumes and concentrations correctly.
  • Since indicators have to be chosen carefully based on their colour change at the endpoint, careful selection is crucial for accurate results.
  • Handle oxidising agents with care as they are usually hazardous – it’s important to wear appropriate safety gear and conduct the experiment in a well-ventilated area.