potentiometric titration
Potentiometric Titration Overview
Potentiometric titration finds the endpoint by measuring changes in electrical potential. Unlike direct methods, it doesn’t require exact electrode potential measurements. This makes it less sensitive to temperature changes and liquid junction potential. As a result, it’s highly accurate, especially when traditional indicators don’t work well with colored or cloudy solutions.
Key Concepts
Different electrodes serve different types of titration:
- Acid-base titration: Uses a pH glass electrode.
- Redox titration: Uses a platinum electrode.
- Complexometric titration: Uses a mercury electrode.
- Precipitation titration: Uses a silver electrode with silver nitrate.
As you add the titrant, the potential changes. At the endpoint, there’s a sharp jump in the potential, making the endpoint easy to detect.
Equipment Required
You’ll need a few key components for potentiometric titration:
- Burette
- Titration cell
- Indicator electrode
- Reference electrode
Determining the Endpoint
The endpoint is marked by a sudden rise in potential, easily spotted using a differential curve, a curve with the potential (E) on the y-axis and the volume of titrant (V) on the x-axis.
Applications of Potentiometric Titration
This method works in many titrations, including acid-base, precipitation, redox, and coordination reactions.
1. Acid-Base Titration
Potentiometric titration is excellent for weak acids and bases in both aqueous and non-aqueous solutions. The pH glass electrode or antimony electrode serves as the indicator, while the calomel electrode acts as the reference.
Examples:
- Pyridine titrated with HClO₄ in acetic acid.
- Triethanolamine titrated with HCl in ethanol.
- Aniline titrated in isopropanol and ethylene glycol.
- Phenol titrated in dimethylformamide.
- Mixed acids (perchloric, hydrochloric, salicylic) titrated in acetone.
2. Precipitation Titration
This method measures halogen ions and other substances forming precipitates. It uses silver, mercury, or platinum electrodes with a calomel reference electrode.
Examples:
- Halogen ion titration (Clˉ, Brˉ, Iˉ) using silver nitrate.
- Mercury nitrate titration for Clˉ, Brˉ, Iˉ, and CNSˉ.
- Platinum electrode titration for Pd²⁺, Cd²⁺, Zn²⁺, and Ba²⁺ using K₄[Fe(CN)₆].
3. Redox Titration
Redox titration measures oxidation state changes, using a platinum electrode. The calomel electrode acts as the reference.
Examples:
- Potassium permanganate titration for Iˉ, NO₃ˉ, Fe²⁺, and Sn²⁺.
- K₄[Fe(CN)₆] titration for Co²⁺.
- Potassium dichromate titration for Fe²⁺, Sn²⁺, and Sb³⁺.
4. Coordination Titration
This method is used to measure metal ions. EDTA is typically used as the titrant. The calomel electrode serves as the reference, and indicator electrodes vary by ion type.
Examples:
- EDTA titration for Cu²⁺, Zn²⁺, Ca²⁺, Mg²⁺, and Al³⁺.
- Fluoride titration of Al³⁺ using a chlorine electrode.
- Calcium ion titration with a calcium ion-selective electrode.
Advantages of Potentiometric Titration
- Works with colored or turbid solutions where traditional indicators fail.
- Suitable for dilute solutions or incomplete reactions.
- Offers high sensitivity and accuracy with the potential for automatic and continuous measurements.
Why Use Potentiometric Titration?
Potentiometric titration stands out for its flexibility and precision. It’s widely used in chemical analysis, from pharmaceuticals to environmental testing. Its ability to handle difficult solutions makes it an essential tool in many industries.