This document discusses the principles and instrumentation of potentiometry. It begins by defining potentiometry as a method used in electroanalytical chemistry to measure electrochemical potential using an electrode system. It then describes the components and working of a potentiometer, including the electrochemical cell and reference/indicator electrodes. Specific instruments like pH meters are also summarized, with details on their setup, calibration process using buffer solutions, and measurement of pH in samples.

1. PRESENTATION TOPIC.
PRINCIPLE AND INSTRUMENTATION
OF POTENTIOMETRY
Submitted To:
Mam Noor-US-Sabah
Made by Muhammad Usman

2. Group 2
Submitted By:
Muhammad Usman BAGF14E256
Abdulmajid BAGF14M069
M.Hamza Dildar BAGF14M045
Ahsan Shahzad BAGF14E268

3. Presentation outline
■ Potentiometry
■ Potentiometer
■ Principle of operation
■ Electrochemical cell
■ Instrumentation
 pH meter

4. Potentiometry
■ A potentiometer is an instrument for
variable potential (voltage) in a circuit.
■ Potentiometry is a method used in electroanalytical chemistry
to measure electrochemical potential of charged particles. An
electrode system is used to measure this potential and detect
ions while other substances are also present. Two electrodes
are placed in an analyte solution and connected to
a potentiometer. Measurements are always made when no or
very little current is present, so the composition of the
substance measured is not altered, making quantitative analysis
possible.

5. Potentiometer
■ An instrument for measuring an electromotive force by
balancing it against the potential difference produced by
passing a known current through a known variable resistance.
or
■ An electronic component that is used to vary, or control, the
amount of current that flows through an electronic circuit.
The method was described by Johann Christian
Poggendorff around 1841.

6. Potentiometer

7. Principle of operation
■ When a cell E’ is introduced with positive connected to A in the
path AGX, it creates opposite field to that created by the driving
cell, and thus when V = E’, no current flows through the portion
AGX which is confirmed by the galvanometer (G). Thus, we get E’
∝d (from principle and the figure).

8. Principle of operation
■ In an electrochemical cell linked by the potentiometer, a reference
electrode is used that has a potential independent from any temperature
or analyte variables. Electrodes used for reference in potentiometry
usually include hydrogen, saturated calomel, or silver chloride. An
indicator electrode is exposed to the analyte solution, and its potential
varies depending on the ions present in the solution. Each electrode is
placed in a separate solution and connected to a single potentiometer
instrument, while a salt bridge is exposed to each sample, completing
an electrical circuit. The purpose of measurements with electrochemical
cells is to calculate ion concentrations using electrode potential.

9. Electrochemical cell
■ An electrochemical cell is a device capable of either
generating electrical energy from chemical reactions or facilitating
chemical reactions through the introduction of electrical energy. A
common example of an electrochemical cell is a standard 1.5-
volt cell meant for consumer use. This type of device is known as a
single Galvanic cell. A battery consists of two or more cells,
connected in either parallel or series pattern.

10. Electrochemical cell

11. Single Galvanic cell
potential depends on
length of wire selected.
(Potential = length *
potential gradient).

12. Instrumentation
■ Instruments used in potentiometry also include pH meters. The pH
defines whether a substance is an acid, base, or neutral, which can
greatly affect potentiometry measurements. In an electrochemical
cell, a reference electrode, called an anode, has a potential
independent from any temperature or analyte variables. An
indicator electrode, often referred to as a cathode, is exposed to the
analyte solution, and its potential varies depending on the ions
present in the solution.

13. pH meter
■ A pH Meter is a scientific instrument that measures the hydrogen-
ion concentration (or pH) in a solution, indicating
its acidity or alkalinity. The pH meter measures the difference in
electrical potential between a pH electrode and a reference
electrode. It usually has a glass electrode plus a calomel reference
electrode, or a combination electrode. In addition to measuring the
pH of liquids, a special probe is sometimes used to measure the pH
of semi-solid substances.

14. pH meter
 The pH meter is a cell consisting of a glass indicator electrode and a
satured calomel reference electrode, immersed in the solution whose pH
value needs to be evaluated.
■ Reference electrode→ Is a half-cell with a precisely known Erif
electrode potential, independent of the analyte concentration, or of any
other ion in the solution being examined. Conventionally the reference
electrode is always treated as anode.
■ Indicator electrode→ Immersed in the analyte solution, develops a
potential, Eind, which depends on the analyte activity
■ The salt bridge→ Prevent the analyte solution components from mixing
with those of the reference electrode.

15. pH meter structure
■ Indicator electrode: consists of a thin glass membrane, sensitive to pH,
soldered to the ends of a reinforced glass tube. This latter contains a
small volume of cloridric acid, diluted and satured with silver chloride.
In this solution a silver thread forms a silver/silver chloride reference
electrode, which is linked to one of the terminals of a potential
measuring instrument.
■ Reference electrode: the calomel electrode (SCE) has a known
potential, which is constant and completely indifferent to the
composition of the analyte solution.

16. Structure of pH meter

17. Working of pH meter:
■ pH meter base on electro-chemical potential in liquid solution and
electron mobility in metal.
■ In two liquid solution case one known solution pleace inside the
glass electrode(membrane) and unknown solution outside.
■ Reference solution internal is 0.01 mol/L KCL.

19. Calibration of pH meter
■ pH meter calibration through through two standard buffer solutions.
■ Many partes are require for the calibration of pH meter such as:
1. Preparing for Calibration:
I. Turn on your pH meter. Before you begin to calibrate and use your
pH meter you will first need to turn it on and allow adequate time for
the meter to warm up. This should generally take around 30 minutes,
but check your pH meter’s operating manual for exact times.
II. Clean your electrode. Take the electrode out of its storage solution
and rinse it with distilled water under an empty waste beaker. Once
rinsed, blot dry with Kim wipes or Shur wipes.

20. Calibration of pH meter
III. Prepare your buffers. You will generally need more than one
buffer for calibrating a pH meter. The first will be a “neutral”
buffer with a pH of 7, and the second should be near the expected
sample pH, either a pH of 4 or 9.21. Buffers with a higher pH (9.21)
are best calibrated for measuring bases, whereas buffers with a low
pH (4) are best for measuring acidic samples. Once you have chosen
your buffers allow them to reach the same temperature, as pH
readings are temperature dependent. Pour your buffers into
individual beakers for calibration.

21. Calibration of pH meter
2 Calibrating Your pH Meter.
I. Place your electrode in the buffer with a pH value of 7 and begin
reading. Press the “measure” or calibrate button to begin reading the
pH once your electrode is placed in the buffer.
 Allow the pH to stabilize before setting by letting it sit for approximately
1-2 minutes.
II. Set the pH. Once you have a stable reading, set the pH meter to the
value of the buffer’s pH by pressing the measure button a
second time. Setting the pH meter once the reading has stabilized will
allow for more accurate and tuned readings.
 Although not necessary, if you stir your buffer before measuring be sure
to stir all other buffers and samples in the same way.

22. Calibration of pH meter
III.Rinse your electrode with distilled water. Rinse and pat dry with a lint-
free tissue, like Kimwipes or Shurwipes, in between buffers.
IV.Place your electrode in the buffer with a pH value of 4 and begin
reading. Press the measure button to begin reading the pH once your
electrode is placed in the buffer.[11]
 If you are not using a buffer with a pH value of 4 for calibration, use the
buffer with a pH value of 9.21.
V. Set the pH a second time. Once your reading has stabilized, set the pH
meter to the value of the buffer’s pH by pressing the measure button.
VI.Rinse your electrode. You can use distilled water to rinse. Use a lint-free
tissue, like Kimwipes or Shurwipes, in between buffers to dry the
electrode.