Learn about the principle, types, and applications of potentiometric titration, that measures the potential between two electrodes as a function of the added reagent volume.
Titration is a commonly used analytical technique in laboratories for estimating the concentration of an analyte in a sample solution since it has various advantages and applications.
Titration is also known as volumetric or titrimetry analysis since volume measurement is significant in titration.
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What is potentiometric titration?
Potentiometric titration is a type of volumetric method used to determine the amount of an analyte by adding measured increments of titrant until the end-point is completed.
Following the titration, the potential difference between the indicator electrode and the reference electrode is determined under conditions where the thermodynamic equilibrium is maintained and the current passing through the electrodes does not disturb it.
It involves determining and recording the cell potential (millivolts or pH) after each titrant addition. To perform the potentiometric titration indicator electrode (metal ion indicator and glass electrode) and a reference electrode are used. The calomel electrodes, hydrogen electrodes, and silver chloride electrodes are commonly used as reference electrodes.
With the interested ions in the sample solution, the indicator electrode forms an electrochemical half cell and the other half cell forms by the reference electrode. The different apparatus used in the potentiometric titration are burette, pipette, conical flask, funnel, beaker, volumetric flask, wash bottle and stand, etc.
Principle of potentiometric titration:
The principle behind the potentiometry is that when a pair of electrodes is placed in a solution, the addition of a titrant or a change in the concentration of ions indicates the potential difference. The reference electrode has its potential value and when it is dipped into sample solution it is stable.
The salt bridge is employed to keep the analyte solution from interfering with the reference solution. The solution whose potential is to be determined is referred to as an analyte solution. The indicator electrode is the one that reacts to changes in the analyte solution's potential.
The total electric potential is calculated as Ecell = Eind - Eref + Esol.
A chemical indicator is not used in this reaction; the electric potential across the material is instead measured.
Types of potentiometric titration:
Potentiometric titration is a laboratory method used in the characterization of acids similar to direct titration of a redox reaction. Potentiometric titration can perform the following 4 types of titrations.
Acid-base titration:
An acid-base titration is a quantitative analysis used to determine the acid or base concentration by precisely neutralizing the acid or base with a known concentration standard solution.
Titration of HCl with NaOH is an example in which a pH indicator (Generally phenolphthalein) is used to produce color by which the equivalence point or endpoint of the reaction determines. It is also can be performed by potentiometric titration however it doesn’t need an indicator.
Redox titration:
It is a type of titration it includes the use of a redox indicator or potentiometer. It works based on an oxidation-reduction reaction between the titrant and the compound. Iodometry, permanganometry, bromatometry, cerimetry, and dichrometry are some of the most used redox titrations. A platinum or calomel electrode is also used in redox titration using a potentiometer.
Complexometric titration:
In this type of potentiometric titration, membrane electrodes are used to determine the concentration of metal ions in the compound sample. In the reaction of this method, a metal indicator complex is formed when the metal ion reacts with the indicator.
Complexometric titration consists of replacement titration, back titration, direct titration, and indirect titration.
Precipitation titration:
It is a titration method that involves the formation of precipitates throughout the process of titration. The titrant reacts with the solute to form an insoluble substance, and the titration is carried until the last drop of the solute has been consumed.
Depending on the type of application it consists of Volhard’s method, Mohr's method, and Fagan’s method.
Applications of potentiometric titration:
- Potentiometric titration is used in environmental analysis.
- It is used in different industries such as pharmaceutical, food, and detergent, etc.
- To detect different elements in soils, fertilizers, etc. it is used in the agriculture sector.
- It is used to determine the equivalence point of an acid-base solution.
- It is broadly used for the assay of several official compounds.
- It is used in clinical chemistry for the analysis of metals
- It is used in environmental chemistry for the analysis of water and wastewater.
Commonly asked questions on potentiometric titration are as follows.
What is the importance of potentiometric titration?
Potentiometry is important for determining a sample solution's electromotive force or potential. The ion concentration is directly proportional to the potential.
What is the electrode used in potentiometric titrations?
In a potentiometric titration, calomel and silver/silver chloride electrodes are most commonly used. A mercurous sulfate electrode can be used in halide determination.
Why are indicators used in titration?
The indicators are used in titration for the detection of endpoints of reactions. The color of an indicator changes when the acidity or oxidizing power of a solution reaches a critical range of values.
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