PHD → Analytical chemistry → Electroanalytical techniques ↓
Conductometry and potentiometry
In the field of electroanalytical techniques in analytical chemistry, conductometry and potentiometry play important roles. These methods are central to understanding the quantitative aspects of chemical analysis through their unique ways to measure chemical properties.
Conductometry
Conductometry revolves around the measurement of electrical conductivity in a solution. The principle here is that the conductivity of a solution is directly proportional to the concentration of ions present in it. This property makes conductometry a powerful tool for analyzing solutions of electrolytes.
Basic principles
The main principle of conductometry is the measurement of the ability of a solution to conduct electricity. This ability is affected by many factors including the concentration of ions, the mobility of the ions, and the valency of the ionic species. Conductivity (G
) is defined as the inverse of resistance (R
), measured in siemens (S
), and is calculated as:
G = 1/R
Where conductivity is affected by the area of the electrodes and the distance between them, which is described as:
G = k * (A/l)
Where:
k
is the cell constantA
is the area of the electrodel
is the distance between the electrodes
Application
Conductometry has wide applications in analytical chemistry, including titrations and the evaluation of water purity. In particular, conductometric titrations eliminate the need for indicators that can interfere with the reaction, leading to clear changes in conductivity as the reaction proceeds.
Example: conductometric titration
During a typical conductometric titration, consider the titration of a base with an acid. As the reaction proceeds, hydrogen ions are replaced by hydroxide ions, and the conductivity changes. This provides a visible endpoint when plotted on a graph.
H 3 O + + OH - → 2H 2 O
This graph shows the sharp change in conductivity at the end point.
Potentiometry
Potentiometry involves measuring the potential (voltage) of an electrochemical cell. This technique measures the electrical potential difference between two electrodes in solution without drawing any significant current from the cell.
Basic principles
In potentiometry, a specific ion electrode and a reference electrode are used. The potential difference between these electrodes is directly related to the concentration of an analyte in the solution. The fundamental equation governing potentiometry is the Nernst equation:
E = E° + (RT/nF) * ln([Red]/[Ox])
Where:
E
is the electrode potentialE°
is the standard electrode potentialR
is the universal gas constantT
is the temperature in Kelvinn
is the number of transferred electronsF
is the Faraday constant[Red]
and[Ox]
are the concentrations of the reduced and oxidized species
Application
Potentiometry is widely used in determining the pH of a solution using a pH electrode and in titrations. It provides accurate measurements of ion concentrations in complex matrices without the need for individual calibration against standards for each ion.
Example: pH measurement
A classic example of potentiometry is measuring pH using a glass electrode. This involves measuring the potential difference that develops across a glass membrane when it comes into contact with the test solution.
The potential difference corresponds to the activity of hydrogen ions, allowing accurate measurement of pH.
Potentiometric titration
Potentiometric titrations involve monitoring the potential of the solution during the titration to detect the end point. Unlike conductometric titrations, they work effectively in turbid and colored solutions, as they are less affected by the presence of particles.
Combination of conductometry and potentiometry
While conductometry and potentiometry are powerful independently, they can also be used together to validate and complement results. A combined approach can establish more reliable endpoints in titrations and analyze complex mixtures with higher accuracy.
Conductometry allows for robust analysis of ionic solubility and precipitation reactions, while potentiometry excels at providing insight into oxidation and reduction reactions. Together, they expand the analytical capability of researchers in studying diverse chemical systems.
Example of integration
Conductometric measurements can provide preliminary information about the progress of a reaction, while potentiometric endpoints confirm the completion of specific steps, such as neutralization or redox potential stabilization in acid–base titrations.
For researchers focusing on electroanalytical techniques, conductometry and potentiometry provide rich data on ion activity and electronegativity that help understand complex biochemical mechanisms and synthesize new compounds with unique electrochemical properties.
In summary, leveraging these methods could transform analytical work, paving the way for advances in environmental testing, pharmaceutical manufacturing, and industrial analysis, and ushering in the next generation of accurate analysis in aqueous systems.