PG electrolyets ppt_Debanjali Sarkar-4.pptx

ELECTROCHEMISTRY
Presented by
Debanjali Sarkar
M. Tech. (Dairy Chemistry)
1st
Semester
Faculty of Dairy Technology
West Bengal University of Animal & Fishery Sciences
Mohanpur, Nadia-741252
2024

I N D E X
 Electrolytes & Non-electrolytes
 Non-Electrolytes
 Electrolytic Dissociation
 Arrhenius Equation
 The Theory of Electrolytic Dissociation
 Ionic Mobility
 Ionic Activity
 Ionic Strength
 Dissociation Constant
 Acids and Bases
 Dissociation Constants for an Acid
 Dissociation Constants for a Base
 Ionic Strength Effect on Dissociation Constant
 Electrode
05/15/2025 2
DC-511: Electrochemistry

I N D E X
 Electrode Potential
 Nernst Equation
 Le Chatelier's Principle
 Buffer
 Henderson–hasselbalch Equation
 Buffer-capacity
 Buffer Index
 Constituents Contributing to the Buffering Capacity of Milk
 Redox Reaction in Milk
 Photo- Oxidation of Milk
 Conclusion
 References
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ELECTROLYTES AND NON-ELECTROLYTES
05/15/2025 DC-511: Electrochemistry 4

ELECTROLYTES & NON-ELECTROLYTES
 Electrolytes
 Substances which cause increase in electrical conductivity in solutions (Sharma,
2019).
 Electrolytes dissociate in the process of conducting the electric current (Sharma,
2019).
 In other words, electrolyte is an electrical conductor (Sharma, 2019).
 Electrolytes conduct current by ions rather than by free electrons (as in a metal)
(Sharma, 2019).
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NON- ELECTROLYTES
A non-electrolyte is a compound that does not conduct electricity when molten or in
aqueous solutions (Sharma, 2019).
Non-electrolytes give the expected result to osmotic pressure, freezing point and
boiling point (Sharma, 2019).
 They do not significantly increase the electrical conductivity (Sharma, 2019).
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ELECTROLYTIC DISSOCIATION
oTo understand electrolytic dissociation, first we have to know about Arrhenius Theory
oAccording to this theory, molecules of an electrolyte on going into solution dissociate
into ions (Sharma, 2019).
oThe ions are dissimilar as to the elements or elements represented in them and as to
the electrical charge which they carry (Sharma, 2019).
oIn each case there are ions that carry positive charge and ions that carry negative
charges (Sharma, 2019).
oThe positive and negative charges ions are present in such a number that two types
just compensate each other (Sharma, 2019).
o So, the resulted solution is electrically neutral or balanced (Sharma, 2019).
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ARRHENIUS EQUATION
In physical chemistry, the Arrhenius equation is a formula for the temperature
dependence of reaction rates.
The Arrhenius equation describes the exponential dependence of the rate constant of
a chemical reaction on the absolute temperature as
k = Ae-Ea/RT
Where,
k is the rate constant (frequency of collisions resulting in a reaction),
T is the absolute temperature,
A is the pre-exponential factor or Arrhenius factor or frequency factor.
Ea is the molar activation energy for the reaction,
R is the universal gas constant.
05/15/2025 8

ARRHENIUS EQUATION
Alternatively, the equation may be expressed as
k = Ae-Ea/k
B
T
Where,
Ea is the activation energy for the reaction (in the same unit as kBT),
kB is the Boltzmann constant. (Arrhenius, S. A.1889)
05/15/2025 9

THE THEORY OF ELECTROLYTIC DISSOCIATION
The theory of electrolyte dissociation explains
 The abnormal behaviors of electrolytes with respect to osmotic pressure, freezing
point and boiling point (Sharma, 2019).
 The electrical conductivity of solutions (Sharma, 2019).
 The facts of electrolysis (Sharma, 2019).
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IONIC MOBILITY
• In the absence of external electrical field, the ions
of a solution are in random motion since all
directions are equivalent (Sharma, 2019).
• When an external electrical field is applied
although the randomness of motion will basically
remain, one of the directions (Sharma, 2019).
• The velocity of an ion is the value of this
preferential migration towards one of the
electrode expressed in cm/s (Sharma, 2019).
• Ionic mobility = Ionic conductance/ 96500
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IONIC ACTIVITY
Ionic activity is a measure of how active individual
ions are in a solution.
It's a parameter that's related to the number density
of ions, but it more realistically expresses the
interactions between ions than molar concentration.
Ionic activity is related to concentration by the
equation 𝑎i =𝛾i𝑐i, where 𝛾i is the activity coefficient.
The activity coefficient can take different forms
depending on how concentration is expressed, such
as molarity, molality, or mole fraction (Pobelov,
2018).
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IONIC STRENGTH
Ionic strength is a unit less quantity that measures
the concentration of ions in a solution, and the total
charge of those ions.
It's calculated using the formula I=1/2∑cizi
2
, where
ci is the molar concentration of each ion and zi is the
charge of each ion.
Ionic strength is important because it affects the
properties of a solution, such as the solubility of salts
and the dissociation constant. (Solomon & Theodros,
2001).
05/15/2025 13

DISSOCIATION CONSTANT

DISSOCIATION CONSTANT
 A general example is the dissociation of the compound AB into A+B which can be
written as AB A + B (Sharma, 2019).
 when a solution is prepared by adding AB, it is possible to calculate from the
dissociation how much of the material added is in the form of AB, A and B which
are constant (Sharma, 2019).
 However, before calculation it is important to know that dissociation of AB into A
and B is a reversible process (Sharma, 2019).
 A and B can assemble back to AB (Sharma, 2019).
 The dissociation constant can be written as Ka = {[A] x [B]}/ [AB] (Sharma,
2019).
05/15/2025 15

ACIDS AND BASES
What is acid?
Arrhenius has proposed that acids are the
substances that produce protons H+ in aqueous
solutions (Sharma, 2019).
What is Base?
 According to Arrhenius, bases are the substances
which produce OH-
(Sharma, 2019).
the behavior of some acids and bases in aqueous
solutions was different (Sharma, 2019).
Acids was that the compounds of which are
capable of donating protons. Similarly bases are the
substance which accepts protons (Sharma, 2019).
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DISSOCIATION CONSTANTS FOR AN ACID
The acid dissociation constant (Ka) is an equilibrium constant that measure the
strength of acids in solution (Sharma, 2019).
The dissociation constant of an acid is used to study the dissociation of weak or
strong acids (Sharma, 2019).
Dissociation constants are often denoted as Ka-values (Sharma, 2019).
A simple example on how to use Ka-values is given here
 Consider ammonium (NH4
+
) dissociating reversibly into ammonia (NH3) (Sharma,
2019).
 NH4
+
NH3 + H+
05/15/2025 17

DISSOCIATION CONSTANTS FOR A BASE
The base dissociation constant (Kb) is a equilibrium constants that measure the strength of
bases in solution (Sharma, 2019).
Acid dissociation constants (𝐾a) and base dissociation constants (𝐾b) are equilibrium constants
for the reactions of acids and bases with water (Sharma, 2019).
The greater the value of an acid's 𝐾a, the stronger the acid (Sharma, 2019).
The greater the value of a base's 𝐾b, the stronger the base (Sharma, 2019).
[H3O+
] [A-
]
Acid Dissociation Constant, Ka=
[HA] Dissociation Constant
[BH+
] [OH-
] Acid and Base Formula
Base Dissociation Constant, Kb =
[HB]
05/15/2025 18

IONIC STRENGTH EFFECT ON DISSOCIATION CONSTANT
The dissociation constant of a solution increases as the ionic strength of the solution
increases.
This is because more ions diffuse into the ionic atmosphere.
For the reaction of an acid HA with water is shown in the diagram.
 The equation shows that the acids which dissociate to a greater extent will have larger
value of Ka are stronger acids while those which have a smaller values of Ka are weaker acids.
(Khouri, 2015)
HA(aq) + H2O(l) A+
(aq) + H3O+
(aq)
[A+
] [H3O+
]
Kaq [H2O] = Ka =
[HA]
05/15/2025 19

IONIC STRENGTH EFFECT ON DISSOCIATION CONSTANT
Similarly for bases Kb with the equation is shown
in the diagram (Sharma, 2019).
Higher equilibrium constant of a base indicates
that it is a strong base (higher ionic strength) while
the smaller value a weak base (lower ionic strength)
(Sharma, 2019).
B(aq) + H2O (l) BH+
(aq) + OH+
(aq)
[BH+
] [ OH+
]
Keq [H2O] = Kb =
[B]
05/15/2025 20

ELECTRODE

ELECTRODE
An electrode is an electrical conductor used to make contact with a nonmetallic part
of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air).
Electrodes are essential parts of batteries that can consist of a variety of materials
(chemicals) depending on the type of battery.
Michael Faraday coined the term " electrode" in 1833; the word recalls the Greek
λεκτρον (ḗlektron, "amber") and δός (hodós, "path, way").
ἤ ὁ
The electrophore, invented by Johan Wilcke in 1762, was an early version of an
electrode used to study static electricity. (Whitaker & Harry ,2007).
05/15/2025 22

ELECTRODE POTENTIAL
In electrochemistry, electrode potential is the voltage of a galvanic cell built from a
standard reference electrode and another electrode to be characterized.
By convention, the reference electrode is the standard hydrogen electrode (SHE). It
is defined to have a potential of zero volts.
It may also be defined as the potential difference between the charged metallic rods
and salt solution.
The electrode potential has its origin in the potential difference developed at the
interface between the electrode and the electrolyte. It is common, for instance, to speak
of the electrode potential of the M+
/M redox couple. (Hamel, 1964)
05/15/2025 23

Standard Electrode Potential of Zinc Electrode

ELECTRODE POTENTIAL
The measurement is generally conducted using a three-electrode setup
i. working electrode,
ii. counter electrode,
iii. reference electrode (standard hydrogen electrode or an equivalent).
 Historically, two conventions for sign for the electrode potential have formed
A. convention "Nernst–Lewis–Latimer" (sometimes referred to as "American"),
B. convention "Gibbs–Ostwald–Stockholm" (sometimes referred to as "European")
05/15/2025 25

Three-electrode setup for measurement of electrode potential

NERNST EQUATION
The Nernst equation has a physiological application when used to calculate the
potential of an ion of charge z across a membrane. (Orna et al., 1989)
This potential is determined using the concentration of the ion both inside and
outside the cell
RT [ion outside cell] RT ion outside cell
E = ln = 2.3026 log10
ZF [ion inside cell] ZF ion inside cell
05/15/2025 27

LE-CHATELIER’S PRINCIPLE

LE CHATELIER'S PRINCIPLE
In chemistry, Le Chatelier's principle is a principle used to predict the effect of a
change in conditions on chemical equilibrium.
Other names include Chatelier's principle, Braun–Le Chatelier principle, Le
Chatelier–Braun principle or the equilibrium law.
The principle is named after French chemist Henry Louis Le Chatelier who
enunciated the principle in 1884 by extending the reasoning from the Van 't Hoff
relation of how temperature variations changes the equilibrium to the variations of
pressure and what's now called chemical potential, and sometimes also credited to Karl
Ferdinand Braun, who discovered it independently in 1887. (Helmenstine & Anne
Marie,2020)
05/15/2025 29

LE CHATELIER'S PRINCIPLE
It can be defined as:
If the equilibrium of a system is disturbed by a change in one or more of the
determining factors (as temperature, pressure, or concentration) the system tends to
adjust itself to a new equilibrium by counteracting as far as possible the effect of the
change
- Le Chatelier's principle, Merriam-Webster Dictionary
In scenarios outside thermodynamic equilibrium, there can arise phenomena in
contradiction to an over-general statement of Le Chatelier's principle.
Le Chatelier's principle is sometimes alluded to in discussions of topics other than
thermodynamics. (Helmenstine & Anne Marie,2020)
05/15/2025 30

BUFFER

BUFFER
Solutions with stable hydrogen ion
concentration and therefore usually with no
change in pH (Sharma, 2019).
 which is almost independent of dilution and
changing very little with small additions of a
strong acid or alkali (Sharma, 2019).
In simple terms it can also be defined as a
solution which resists any change of pH when a
small amount of a strong acid or a strong base is
added to it, is called a buffer solution or simply as
a buffer (Sharma, 2019).
buffers have acidity and reserve alkalinity
(Sharma, 2019).
05/15/2025 32

BUFFER
There are two types of buffers, acid buffer and basic buffer.
A buffer solution containing large amounts of a weak acid, and its salt with a strong
base, is termed as an acid buffer.
Acid buffer solutions have pH on the acidic side i.e., pH is less than 7 at 298 K.
The pH of an acid buffer is given by the equation in the diagram. CH3COOH and
CH3COONa
Where Ka is the acid dissociation constant of the weak acid
[salt]
 pH = pKa + ln
[acid]
05/15/2025 33

BUFFER
A buffer solution containing relatively large amounts of a weak base and its salt with
a strong acid is termed as a basic buffer.
Such buffers have pH on the alkaline side i.e., pH is higher than 7 at 298 K. e.g.:
NH4OH and NH4Cl
The pH of a basic buffer is given by the equation in the diagram.
Where Kb is the base dissociation constant of the weak base.
These equations are called Henderson Hasselbalch equations.
[salt]
 pOH = pKb + ln
[base]
05/15/2025 34

HENDERSON–HASSELBALCH EQUATION
In chemistry and biochemistry, the Henderson–Hasselbalch equation
[Base]
pH = pKa + log10
[Acid]
relates the pH of a chemical solution of a weak acid to the numerical value of
the acid dissociation constant, Ka, of acid and the ratio of the
concentrations, [Base]/[Acid] of the acid and its conjugate base in an equilibrium
(Sharma, 2019).
05/15/2025 35

GOOD'S BUFFER
Good's buffers (also Good buffers) are twenty buffering
agents for biochemical and biological research selected and described by Norman Good
and colleagues during 1966–1980.
Most of the buffers were new zwitterionic compounds prepared and tested by Good and
coworkers for the first time, though some (MES, ADA, BES, Bicine) were known
compounds previously overlooked by biologists.
Before Good's work, few hydrogen ion buffers between pH 6 and 8 had been accessible
to biologists, and very inappropriate, toxic, reactive and inefficient buffers had often been
used.
 Many Good's buffers became and remain crucial tools in modern biological laboratories.
Because most biological reactions take place near-neutral pH between 6 and 8, ideal
buffers would have pKa values in this region to provide maximum buffering capacity there
(Good et al.,1966).
05/15/2025 36

BUFFER-CAPACITY
The effectiveness of any buffer is described in
terms of its buffer capacity.
It is defined as, 'the number of equivalents of a
strong acid (or a strong base) required to change the
pH of one litre of a buffer solution by one unit,
keeping the total amount of the acid and the salt in
the buffer constant.
The buffer capacity of a buffer is maximum when
acid to salt or base to salt ratio is equal to 1 i.e., it
contains equal number of moles of acid (or base)
and the salt (Sharma, 2019).
05/15/2025 37

BUFFER INDEX
This can be defined as the differential ratio of the increase in
the amount of strong acid or strong base added, to pH variation
(Sharma, 2019).
The number of gram equivalents of acid or base that must be
added to one liter of a buffer solution to change its pH by one
unit.
β = dB/dpH, where is the buffer index, is the number of
𝛽 𝑑𝐵
gram equivalents of acid or base added to one liter of buffer
solution, and ( ) is the change in pH after the addition of acid
𝑑 𝑝𝐻
or base.
The field of application of both notions is different: the buffer
capacity is used in the quantitative chemical analysis and the
buffer index in studying biological systems.
05/15/2025 38

CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK
Milk contains many acidic and basic groups.
These groups have a buffering action.
The buffering capacity of solution can be expressed
as which is the molar quantity of acid or base needed to
change the pH of 1 litre of solution by one unit.
Where n is number of equivalents of added strong
base. Note that addition of dn moles of acid will change
pH by exactly the same value but in opposite direction.
 β= dn/dpH
05/15/2025 39

CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK
The ionizable groups of the proteins, the phosphates, and the citrates mainly
determine the acidity and the buffering capacity of milk.
There will be variation in the titration curves due to the considerable variation in the
concentration of these substances.
Ionizable groups of the whey proteins and casein molecules are not exposed.
05/15/2025 40

CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF
MILK
Test Samples Buffering Capacity (%)
Lactogen 15.29
Nestogen 9.21
Nan 11.92
Farex 18.56
Lactodex 20.13
Amul Spray 18.48
Positive Control 0.05
Negative Control 0.08
05/15/2025 41

MILK
 The presence of Ca2+
ions strongly modifies the ionization of di and triprotic acids
such as phosphoric acid and citric acid.
 Lowering of the pH of milk will make calcium phosphate soluble because it is not
soluble in normal pH of milk whereas colloidal phosphate will increase when the
pH is increased.
 The Magnesium citrate and protein affect the composition and quantity of colloidal
phosphate (Sharma, 2019).
05/15/2025 42

MILK

REDOX REACTIONS IN MILK

REDOX REACTION IN MILK
 The oxidation reduction reactions involve transfer of electrons between atoms or
molecules.
 Transfer of oxygen (O) or hydrogen (H) or both also may occur.
 Oxidation is loss of electrons while reduction is the gain of electrons.
 In a redox system when half of the system is having oxidation reaction and the other
half is having a reduction reaction, there will be no flow of electrons either in to the
system or go out of the system.
 In normal milk there are several complicated biological systems with varying
composition and concentration.
 In addition to this microorganism gaining entry in to milk contribute certain redox
systems to it depending upon the type of the organisms.
05/15/2025 45

Methylene blue is reduced by freshly drawn milk when it is drawn from udder
anaerobically indicating a more negative potential than methylene blue system.
 Apart from this the chief oxidation and reduction systems present in milk are
Ascorbate, lactate and riboflavin.
05/15/2025 46

 The ascorbic content of fresh milk is about 0.25 meq litre-1.
 the milk is drawn from the udder, all the ascorbate present in milk will be in its
reduced form but reversible oxidation to dehydro ascorbate occurs at rates
dependent on temperature, copper (Cu) and oxygen (O2) concentration.
 Preventing the contamination with copper (Cu) and by deaeration the ascorbate
content can be preserved.
05/15/2025 47

 The redox potential E0 of milk and standard potential E0 of some important systems
in milk are plotted against pH is presented in the Fig.
 Individual milk samples in equilibrium with air generally have Eh’s in the range of
+0.25 to +0.35 V at 25 at their normal pH of milk i.e 6.6 to 6.7.
℃
 Fresh raw whole milk will reduce 0.6 to 0.8 m mol of ferricyanide to ferrocyanide
per liter at 50 for 20 min.
℃
05/15/2025 48

 Concentration of lactate-pyruvate system in
milk is negligible.
 Enzymatic activation of this system would
influence the redox system.
 At higher pH the aldehyde group of lactose is
oxidizable to carboxyl group, but this reaction is
not a reversible and hence it will not influence the
Eh at pH of 6.6.
Redox reactions in milk systems are influenced
by heat treatment, by concentration of O2 and
metal ions such as Cu2+
, by exposure to light and
by oxido redcutases of milk and or micro
organisms (Sharma, 2019).
05/15/2025 49

PHOTO-OXIDATION OF MILK

PHOTO- OXIDATION OF MILK
 Photo-oxidation is a process that occurs in milk when it is exposed to light, which
can degrade the milk's proteins, lipids, and vitamins.
 This can lead to a loss of nutritional value and sensory characteristics, and can make
the milk taste and smell off.
 Photo-oxidation can occur during storage, transportation, and display in grocery
stores.
 Milk and other lipid containing products are susceptible to oxidative deterioration.
 Light from either natural or artificial sources catalyzes certain chemical reactions,
resulting in the development of off flavors and the breakdown of pigments and
‐
vitamins.
05/15/2025 51

PHOTO- OXIDATION OF MILK

CONCLUSION
In a nutshell, it can be concluded that electrochemistry deals with the facts like
electrolytes, non-electrolytes, dissociation of electrolytes, ionic mobility, ionic strength,
ionic activity, acids, bases, dissociation constant of acids and bases, buffers, redox
reaction in milk, photo-oxidation of milk etc.
Electrochemical techniques are used to analyze milk for a variety of substances,
including antioxidants, heavy metals, and endocrine disruptors. For some electro
analytical procedures, it is also necessary to employ milk pretreatment processes before
running the electrochemical test. These pre-treatment steps can be comprised of acid
digestion, centrifugation, filtration, etc., and finally dilution with a buffer or
electrolyte.
05/15/2025 53

REFERENCES
Sharma. K. P, 2019,Physical chemistry of milk
Whitaker, Harry (2007). Brain, Mind and Medicine: Essays in eighteenth-century
neuroscience. New York, NY: Springer. p. 140. ISBN 978-0387709673.
Orna, M. V., Stock, John (1989). Electrochemistry, past and present. Columbus, OH:
American Chemical Society. ISBN 978-0-8412-1572-6. OCLC 19124885
Arrhenius, S. A. (1889). "Über die Dissociationswärme und den Einfluß der
Temperatur auf den Dissociationsgrad der Elektrolyte". Z. Phys. Chem. 4: 96–
116. doi:10.1515/zpch-1889-0408
Abbas, Z. & Ahlberg, E. 2019. Activity Coefficients of Concentrated Salt Solutions:
A Monte Carlo Investigation, Journal of Solution Chemistry, 48(17), pp. 1222-1243.
05/15/2025 54

REFERENCES
Petrucci, R., H., Harwood., William, S., Herring, F. Geoffrey (2002). General
Chemistry (8th ed.). Prentice Hall. p. 718. ISBN 0-13-014329-4.
Good, N. E., Izawa, Seikichi (1972). Hydrogen ion buffers. Methods Enzymol.
Vol. 24. pp. 53–68. doi:10.1016/0076-6879(72)24054-x. ISBN 978-0-12-181887-
6. PMID 4206745
Anson, F. C.; "Common sources of confusion; Electrode Sign Conventions," J.
Chem. Educ., 1959, 36, p. 394.
Atkins, P.W. (1993). The Elements of Physical Chemistry (3rd ed.). Oxford
University Press.
Münster, A. (1970), Classical Thermodynamics, translated by E.S. Halberstadt,
Wiley–Interscience, London, ISBN 0-471-62430-6.
05/15/2025 55

T H A N K Y O U
05/15/2025 56

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