Republic of the Philippines

BATANGAS STATE UNIVERSITY

The National Engineering University
Alangilan Campus
Golden Country Homes, Alangilan, Batangas City, Batangas, Philippines 4200
Tel Nos.: (+63 43) 425-0139 loc. 2121 / 2221
E-mail Address: ceafa@g.batstate-u.edu.ph | Website Address: http://www.batstate-u.edu.ph

College of Engineering
Department of Electronics

SUMMARY OF REPORT
“ POTENTIOMETRY”

Presented to:
Engr. Apryll Joy A. Hernandez Batangas
State University Alangilan, Batangas
City

In Partial Fulfillment of
the Requirements for
Che 437 – Analytical Instrumentation
Bachelor of Science in Instrumentation and Control Engineering

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WHAT IS ELECTROANALYTICAL METHODS?

Electroanalytical methods are techniques used in analytical chemistry to study and

analyze chemical substances through electrochemical reactions occurring in an electrochemical
cell. These methods involve applying an electric potential to a sample solution, which induces
chemical reactions at the electrode surfaces. By measuring the resulting electrical currents or
potentials, information about the analyte's concentration, composition, and other characteristics
can be determined. Electroanalytical methods are widely used in various fields, including
environmental monitoring, pharmaceutical analysis, and biochemical research.

Voltammetry, potentiometry, and coulometry are all electroanalytical techniques used in

analytical chemistry to determine various properties of chemical substances through
electrochemical reactions. Here's a brief overview of each:

Voltammetry: involves measuring the current flowing through an electrochemical cell as a function of
the applied potential. In this technique, the potential applied to the working electrode is varied, and the
resulting current response is recorded. By analyzing the relationship between the applied potential and
the measured current, information about the analyte's concentration, identity, or other properties can be
obtained. Voltammetry is often used for studying redox reactions and detecting trace amounts of
analytes.

Potentiometry: is a technique used to measure the potential difference (voltage) between two electrodes
in a chemical system. One of the electrodes, called the indicator electrode, is sensitive to changes in the
analyte concentration, while the other electrode, known as the reference electrode, maintains a constant
potential. By measuring the potential difference between these electrodes, the concentration of the analyte
can be determined. Potentiometry is commonly used in pH measurements, ion selective electrode (ISE)
measurements, and titrations.

Coulometry: involves measuring the amount of charge passed through an electrochemical cell during
an electrolysis process. By monitoring the amount of charge required to convert the analyte species of
interest, information about its concentration or quantity can be determined.
Coulometry is often used for quantitative analysis, particularly in titrations and determination of electroactive
species.
WHAT IS POTENTIOMETRY?

Potentiometry is a technique used in analytical chemistry to determine the concentration of an

analyte in a solution by measuring the voltage or potential difference between two electrodes in a
chemical system. In potentiometry, one of the electrodes, known as the indicator electrode, responds to
changes in the analyte concentration, while the other electrode, called the reference electrode, maintains
a stable potential. By measuring the potential difference between
these electrodes, typically using a voltmeter, the concentration of the analyte can be determined. Potentiometry
is widely used in various applications, including pH measurements, ion selective electrode (ISE) measurements,
and titrations.

PRINCIPLE

The principle of potentiometry is based on the relationship between the concentration of an analyte
in a solution and the potential difference (voltage) between two electrodes in an electrochemical cell.
When an analyte undergoes a chemical reaction at an electrode surface, it can cause changes in the local
concentration of ions or electrons, which in turn affects the electrical potential at that electrode. By
measuring the potential difference between a reference electrode with a stable potential and an indicator
electrode sensitive to changes in the analyte concentration, it's possible to determine the concentration of
the analyte in the solution. The potential measured at the indicator electrode reflects the equilibrium
between the analyte and the electrode surface, providing information about the analyte's concentration
without the need for chemical reactions or indicators. This principle forms the basis of potentiometric
measurements used in various analytical techniques.

COMPONENTS OF POTENTIOMETRIC CELLS:

Reference Electrode: The reference electrode provides a stable and known potential
against which the potential of the indicator electrode is measured. Common reference
electrodes include the silver/silver chloride electrode and the calomel electrode.

Salt Bridge: The salt bridge is a porous barrier filled with an electrolyte solution that completes
the circuit between the reference and indicator electrodes while preventing mixing of the
solutions in the two compartments of the cell.

Analyte: The analyte is the substance whose concentration is being measured. It

interacts with the indicator electrode, causing changes in the electrode potential that can be
measured.
 Indicator Electrode: The indicator electrode is sensitive to changes in the concentration of the
analyte. It generates a potential that varies with the concentration of the analyte in the solution.

Potentiometer: The potentiometer is an electronic device used to measure the potential

difference (voltage) between the reference and indicator electrodes. It allows for accurate
determination of the potential difference, which is used to quantify the concentration of the
analyte.

POTENTIOMETRIC TITRATION

Potentiometric titration is a method utilized to determine the quantity of a test substance by

gradually adding a titrant until the entire substance undergoes reaction. Following the titration process,
the potential difference between two electrodes, namely the reference and indicator electrodes, is
measured under conditions of thermodynamic equilibrium, ensuring that the current flowing through the
electrodes does not disrupt this equilibrium.

This laboratory technique is employed to ascertain the concentration of a specific analyte, often used in
characterizing acids. Unlike traditional titration methods that employ chemical indicators, potentiometric
titration relies on measuring the electric potential across the substance.

Potentiometric titrations can be categorized into various types:

- Acid-base titration: This form determines the concentration of an acid or base by neutralizing it
precisely with a standard solution of the opposite type.

- Redox titration: Involving an analyte and titrant undergoing a redox reaction, such as treating an
iodine solution with a reducing agent to produce iodide ions, often indicated by a starch indicator.

- Complexometric titration: Also known as chelatometry, this method involves the formation of a
colored complex to indicate the endpoint, commonly used for determining metal ion mixtures in a
solution.

- Precipitation titration: This type entails a reaction between the analyte and titrant resulting in the
formation of an insoluble precipitate. The titration endpoint is reached when the addition of the titrant no
longer yields a precipitate.
APPLICATION

Potentiometry, a versatile analytical technique, finds numerous applications across various fields. Some
of the key applications include:

Acid-Base Titration: Potentiometry is widely employed in determining the acidity or alkalinity of

a solution through acid-base titration. This is crucial in industries such as pharmaceuticals, food
and beverage, and environmental monitoring.

Redox Titration: Potentiometric redox titrations are used to determine the concentration of
oxidizing or reducing agents in a sample. This is vital in chemical process control, environmental
analysis, and quality assurance in manufacturing.

Complexometric Titration: Potentiometric complexometric titrations are utilized to determine the

concentration of metal ions in solution, particularly in environmental analysis, metallurgy, and
pharmaceuticals.

pH Measurement: Potentiometric pH measurements are essential in various industries, including

agriculture, biotechnology, and water treatment, to monitor and control the acidity or alkalinity
of solutions.

Electroplating: Potentiometry is used to monitor and control the electroplating process by measuring the
concentration of metal ions in the plating bath, ensuring the quality and consistency of plated products.
WHAT IS COULMETRY?

Coulometry is a quantitative analytical technique based on the measurement of the amount of

electricity required to bring about a specific chemical change. In coulometric analysis, the quantity of a
substance is determined by measuring the amount of electric charge (coulombs) passed during an
electrolysis process. This technique is particularly useful for determining the concentration of substances
in solution, especially those that cannot be easily titrated by traditional volumetric methods. Coulometry
finds applications in various fields, including chemistry, environmental analysis, pharmaceuticals, and
electroplating industries.

PRINCIPLE

The principle of coulometry is based on Faraday's laws of electrolysis, which state that the amount
of substance produced or consumed during an electrolysis process is directly proportional to the quantity
of electric charge passed through the electrolytic cell. In coulometry, the amount of substance being
analyzed is determined by measuring the amount of electric charge (in coulombs) required to complete a
specific chemical reaction. During coulometric analysis, an electric current is passed through the
electrolyte solution containing the analyte.
The analyte undergoes a chemical reaction that involves the transfer of electrons, resulting in the
formation of a product or a change in the oxidation state of the analyte. The quantity of the analyte can
be calculated by measuring the total charge passed through the cell and applying Faraday's laws.

TYPES OF COULMETRY

Controlled-Potential (Potentiostatic) Coulometry: In this method, the potential between the

working electrode and a reference electrode is controlled at a constant value. The amount of electricity
required to maintain this potential is measured, and it's used to determine the quantity of the substance
being analyzed. This type of coulometry is often used when precise control over the potential is important.

Principle: In potentiostatic coulometry, the potential difference between the working electrode and a
reference electrode is held constant throughout the analysis.

Setup: A potentiostat is used to maintain the desired potential between the electrodes.

Process: As the electrochemical reaction proceeds, the amount of current passing through the cell is measured
over time. This current is directly proportional to the amount of substance undergoing reaction.
 Applications: Potentiostatic coulometry is often used for precise measurements, especially when the
reaction kinetics are well understood and controlled. It's commonly employed in the analysis of metals,
organic compounds, and redox-active species.

Controlled-Current (Amperostatic) Coulometry Here, a constant current is applied between the

working and counter electrodes. As the electrochemical reaction progresses, the potential between the
electrodes may change. The amount of electricity passed during the reaction is measured, providing
information about the quantity of the substance being analyzed.
Controlled-current coulometry is useful when maintaining a constant current is more critical than maintaining a
constant potential.

Principle: In amperostatic coulometry, a constant current is applied between the working and counter electrodes.

Setup: An amperostat is used to maintain the desired current throughout the analysis.

Process: As the reaction progresses, the potential between the electrodes may change due to changes in the
concentration of reactants and products. However, the current remains constant. The total charge passed during
the reaction is measured and used to determine the quantity of the substance of interest.

Applications: Amperostatic coulometry is useful when maintaining a constant current is more critical than a
constant potential. It's often employed in the analysis of substances where reaction kinetics may vary, such as in
complex matrices or with samples prone to side reactions.

INSTRUMENTATION

The instrumentation used in coulometry typically involves several key components to control the
electrochemical reaction and measure the amount of electricity passed.

Electrochemical Cell: The electrochemical cell consists of at least three electrodes: a working
electrode, a reference electrode, and a counter electrode. These electrodes are immersed in an
electrolyte solution containing the sample being analyzed. The working electrode is where the
electrochemical reaction of interest occurs. The reference electrode provides a stable reference
potential against which the potential of the working electrode is measured. The counter electrode
completes the electrical circuit and ensures a balanced flow of current in the cell

Potentiostat/Amperostat: A potentiostat or amperostat is used to control the potential or

current, respectively, between the working electrode and the reference electrode.For controlled-
potential (potentiostatic) coulometry, a potentiostat is employed to maintain a
 constant potential. For controlled-current (amperostatic) coulometry, an amperostat is used to
maintain a constant current.

Data Acquisition System: A data acquisition system is employed to measure and

record the electrical parameters of the electrochemical cell, such as potential and current.
This system may include a computer interface and specialized software for data
collection and analysis.

Electrolyte Solution:

The choice of electrolyte solution depends on the specific electrochemical reaction being studied and the
properties of the sample. The electrolyte solution should provide sufficient conductivity and stability to
support the desired electrochemical processes.

Calibration Standards: Calibration standards are used to calibrate the instrumentation and
validate the accuracy of the measurements. These standards may consist of known concentrations
of the substance being analyzed or standardized solutions with known properties.

Safety Measures: Safety measures, such as fume hoods and protective equipment, may be
necessary when working with certain substances or electrolytes that pose health or safety risks.

APPLICATIONS OF COULMETRY

 Quantitative Analysis in Electroplating:

 Coulometry is extensively used in electroplating industries to determine the thickness and

composition of metal coatings on surfaces.
 By measuring the amount of electricity required to deposit a metal from a solution onto a
substrate, coulometry enables precise control over the plating process.

· Determination of Purity in Pharmaceutical and Chemical Industries:

 Coulometry is employed for determining the purity of substances in pharmaceuticals,

chemicals, and other industrial products.
 By measuring the amount of electricity required to undergo a specific electrochemical
reaction, the concentration of a substance in a sample can be accurately determined.
· Environmental Analysis:

 Coulometry plays a role in environmental analysis, particularly in assessing the

concentration of pollutants and contaminants in air, water, and soil samples.
 It can be used to quantify the levels of heavy metals, organic pollutants, and other
substances of environmental concern.

· Battery Research and Development:

 In the field of battery research and development, coulometry is employed to study

electrode processes, measure charge-discharge capacities, and evaluate the performance of
battery materials.
 Coulometric techniques provide insights into the electrochemical behavior and efficiency of
batteries, aiding in the development of improved energy storage systems.

Comparison and Distinction of Potentiometry, Coulometry, & Voltammetry

Potentiometry, coulometry, and voltammetry are all electrochemical techniques used in analytical
chemistry, but they differ in their principles, methodologies, and applications. Here's a comparison and
distinction of these three techniques:omparison and Distinction of Potentiometry, Coulometry, &
Voltammetry

Principle:

Potentiometry: Potentiometry measures the electrical potential difference between two electrodes
in a solution, typically using a reference electrode and an indicator electrode.

Coulometry: Coulometry measures the quantity of electricity passed during an electrolysis

reaction to determine the amount of substance present.

Voltammetry: Voltammetry involves applying a potential to an electrochemical cell and

measuring the resulting current to understand the behavior of species in solution.

Methodology:

Potentiometry: Involves immersing two electrodes (a reference electrode and an indicator

electrode) into the solution of interest and measuring the potential difference between them.

Coulometry: Requires passing a known quantity of electric charge through the solution and
measuring the resulting change in the concentration of the analyte or the production of a product.

1. Voltammetry: Involves applying a varying potential to the working electrode while measuring the
resulting current, typically using a three-electrode system (working electrode, reference electrode, and
counter electrode).
 2.

Applications:

Potentiometry: Commonly used in pH measurement, ion selective electrode (ISE) measurements,

and titrations.

Coulometry: Widely employed in quantitative analysis to determine the amount of a substance

present, particularly in coulometric titrations and electrolysis-based analyses.

Voltammetry: Utilized for studying redox reactions, characterizing electrode processes,

determining concentrations of electroactive species, and detecting trace levels of analytes in
various samples.

Sensitivity and Selectivity:

Potentiometry: Generally offers high selectivity, especially with ion-selective electrodes, but
may lack sensitivity for some applications.

Coulometry: Can provide high sensitivity and precision for determining the quantity of substance
present but may be less selective than other methods.

Voltammetry: Offers both high sensitivity and selectivity, especially when coupled with
techniques like differential pulse voltammetry or square wave voltammetry.

Instrumentation:

Potentiometry: Requires a potentiometer or pH meter along with appropriate electrodes,

including a reference electrode and an indicator electrode.

Coulometry: Requires a coulometer, which may vary depending on the specific type of
coulometric technique being employed.

Voltammetry: Requires a potentiostat/galvanostat to control the potential or current applied to

the working electrode and to measure the resulting current or potential.

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