1. CHM 4102
ELECTROCHEMISTRY
GROUP 1

2. NORSHAFIDAH BT ABU SHAFIAN 151897
GOH RUO ZHEN 152008
SITI ZAHARAH BT SYED RAMLI 152197
HEE WAI SUM 152584
LU CHING CHING 153165
LING KAI SING 153168
LYE FUI FANG 153560
ARINA BT IRMAN 153487
NUR SYAZLIANA BT MALIK 153367
THEN PAY KEE 154380

4. INTRODUCTION
 An electrochemical cell is a device in which electron
transfer in a redox reaction are made to pass through an
electric circuit.
 Oxidation process – loss of electron, the substance
oxidized is the reducing agent.
 Reduction process – gain of electron, the substance
reduced is the oxidizing agent.
 Two types of cell :
 Galvanic cell / voltaic cell
 Electrolytic cell

6. •A galvanic cell is an
electrochemical cell
that produces electricity
as a result of the
spontaneous reaction.
•Also called as voltaic
cell

7. Component of Galvanic cell
 The 2 metals are connected by a wire
 The 2 containers are connected by a salt bridge
 A voltmeter is used to detect voltage generated
 example:
i- Zn metal in an aqueous solution of Zn2+
ii- Cu metal in an aqueous solution of Cu2+

8. Galvanic cell

9. What happens at zinc electrode?
 Zn is more electropositive than Cu
 Zn has a tendency to release electron
Zn(s) Zn2+(aq) + 2e-
 Zn dissolves
 Oxidation occurs at Zn electrode
 Zn2+ ions enter ZnSO4 solution
 Zn is the negative electrode (anode)

10. What happens at copper electrode?
Cu2+(aq) + 2e- Cu(s)
 The electron move from negatives to positive
terminal
 Cu2+ ions from the solution accept electrons and the
blue colour of copper(II) solution fades
 Cu is deposited
 Reduction occurs at the Cu electrode
 Cu is the positive electrode (cathode)

11. Cell Notation
Anode: Zn(s) Zn2+(aq) + 2e-
Cathode: Cu2+(aq) + 2e- Cu(s)
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)
Also can be represented as:
Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)

12.  An electrolytic cell is
an electrochemical
cell in which a non-
spontaneous
reaction occur.

13.  It is made up of two electrodes immersed in an
electrolyte
 A direct current is passed through the electrolyte
from an external source
 Molten salt and aqueous solution are commonly
used as electrolytes

14. Differences between Electrolytic and
Galvanic cell
Characteristic Electrolytic cell Galvanic cell
Energy change Electrical energy Chemical energy
Chemical energy Electrical energy
Electric current and Electric current results in a Chemical reaction produces
reaction chemical reaction an electric current
Cathode : Negative terminal Positive terminal
Anode: Positive terminal Negative terminal
Negative terminal Cation receives electrons Electrons are released at the
from the cathode negative terminal
Positive terminal Anions release electrons to Electrons are received by the
the anode positive terminal

15.  Include the working electrode, reference electrode, and
the auxiliary electrode.
 The three electrodes are connected to the power
source, which is a specially designed circuit for precise
control of the potential applied to the working electrode
and often called a potentiostat or polarograph.
 This electrode system is important in voltammetry.
 Voltammetry is an electrochemical technique in which
the current-potential behaviour at an electrode surface
is measured.

17. Auxiliary Electrode
 Counter or Auxiliary electrode : electrode in the cell that
completes the current path.
 All electrochemistry experiments (with non-zero current)
must have a working – counter pair.
 Auxiliary electrode makes sure that current does not pass
through the reference cell. It makes sure the current is
equal to that of the working electrode's current.

18. Reference electrode
 Serve as experimental reference points.
 Specifically they are a reference for the potential (sense)
measurements.
 Reference electrodes should hold a constant potential
during testing.
 Example: Saturated Calomel, Silver/Silver Chloride,
Mercury/Mercury (mercurous) Oxide,
Mercury/Mercury Sulfate, Copper/Copper
Sulfate, and more.

19. Working Electrode
 Working electrode is the designation for the electrode
being studied.
 In corrosion experiments, this is likely the material that
is corroding.
 In physical echem experiments, this is most often an
inert material— commonly gold, platinum or carbon—
which will pass current to other species without being
affected by that current.

21. ELECTROLYTE
Electrochemical reactions occur in a medium, a solvent
containing a supporting electrolyte which is mobile and support
current flow.
 A medium containing mobile ions must exist between the
electrodes in an electrochemical cell to allow for measurement
of the electrode potential.
 Electrolyte provides the pathway for ions to flow between and
among electrodes in the cell to maintain charge balance.

22. Liquid Electrolytes
- Include molten salts and
appropriate solvents
Electrolytes
Solid Electrolytes
- Solids and some of those are
crystalline solids

23. Liquid
Electrolytes
Molecular Liquids Ionic Liquids Atomic Liquids
Aqueous (water) Molten salts and
usually used at Super Atomic
Mixed aqueous Electrolyte (SPE)
relatively high
(water and temperatures Metallic mercury
cosolvent) Blend of a solvating
Nonaqueous (organic Mixtures of organic polymer and a salt or
or inorganic solvent) a nonaqueous
halides with electrolyte solution
aluminium trichloride
Exhibit various liquid
electrolytes properties

24.  Choice-solubility of the analyte , its redox activity, and by
solvent properties(electrical conductivity, electrochemical
activity, and chemical activity)
 The solvent should not react with the analyte (or products) and
should not undergo electrochemical reactions over a wide
potential range.

25. PROPERTIES OF SOLVENTS
Physical Chemical
 Boiling point  Acidity
 Melting point  Basicity
 Vapor pressure
 Heat of vaporization
 Relative permittivity

26. EFFECT OF SOLVENT PROPERTIES ON CHEMICAL
REACTION
Solvents with WEAK ACIDITY Solvents with STRONG ACIDITY
• Solvation to small anions is difficult • Solvation to small anions is easy
-Small anions are reactive -Small anions are nonreactive
• Proton donation from solvent is difficult • Proton donation from solvent is easy
-pH region is wide on the basic side -pH region is narrow on the basic side
-Strong bases are differentiated -Strong bases are leveled
-Very weak acids can be titrated -Very weak acids cannot be titrated
• Reduction of solvent is difficult • Reduction of solvent is easy
-Potential region is wide on negative -Potential region is narrow on negative
side side
-Strong reducing agent is stable in the -Strong reducing agent is unstable in
solvent the solvent
-Strong oxidizing agent is stable in the -Strong oxidizing agent is unstable in
solvent the solvent
-Substances difficult to reduce can be -Substances difficult to reduce cannot
reduced be reduced

27. Solvents with WEAK BASICITY Solvents with STRONG BASICITY
• Solvation to small cations is difficult • Solvation to small cations is easy
-Small cations are reactive -Small cations are nonreactive
• Proton acceptance by solvent is difficult • Proton acceptance by solvent is easy
-pH region is wide on the acidic side -pH region is narrow on the acidic side
-Strong acids are differentiated -Strong acids are leveled
-Very weak bases can be titrated -Very weak bases cannot be titrated
• Oxidation of solvent is difficult • Oxidation of solvent is easy
-Potential region is wide on positive -Potential region is narrow on positive
side side
-Strong oxidizing agent is stable in -Strong oxidizing agent is unstable in
the solvent the solvent
-Substances difficult to oxidize can be -Substances difficult to oxidize cannot
oxidized be oxidized

28. 1. A large number of the ions of one species should be mobile. This requires a large
number of empty sites, either vacancies or accessible interstitial sites.
 Empty sites are needed for ions to move through the lattice.
2. The empty and occupied sites should have similar potential energies with a low
activation energy barrier for jumping between neighboring sites.
 High activation energy decreases carrier mobility, very stable sites (deep
potential energy wells) lead to carrier localization.
3. The structure should have solid framework, preferable 3D, permeated by open
channels.
 The migrating ion lattice should be ―molten‖, so that a solid framework of the
other ions is needed in order to prevent the entire material from melting.
4. The framework ions (usually anions) should be highly polarizable.
 Such ions can deform to stabilize transition state geometries of the migrating
ion through covalent interactions.

30. Liquid Electrolytes VS. Solid Electrolytes
 Liquid electrolytes show generally better leveling capabilities for both temperature and
concentration discontinuities and allow for small volume changes due to chemical or
electrochemical reactions.
 Liquid electrolytes maintain a permanent interfacial contact at the electrolyte or
electrode interface and have generally higher conductivities.
 Liquid electrolytes is capable to dissolve the reaction products; they may hence be
used in electro synthesis as reaction media.
 Liquid electrolytes are potential gassing and leakage problems in cells, and the higher
effort in assembling cells.
 Solid electrolytes often offer cationic or anionic transport in contrast to liquid
electrolyte, where anions and cations are contributing to the conductivity. Avoids the
need for a separator. However, their electronic conductivity may be detrimental in
some applications

31. What to consider in choosing electrolytes?
 Conductivity
 Mobility of active species
 Temperature
 Chemical thermal stability
 Electrochemical stability
 Solubility
 Viscosity

32. Supporting Electrolyte
 An electrolyte containing chemical species that are not
electroactive (within the range of potentials used)
 which has an ionic strength and conductivity much larger
than those due to the electroactive species added to the
electrolyte.
 Inert electrolyte / inactive electrolyte
 The typical concentration of the supporting electrolyte is
0.1 to 1.0 mol/kg

33. Maintain constant
ionic strength and
constant pH
↑
↓ resistance conductivity
Functions of the
solution
eliminate the contribution of
the analyte to the migration
current & ↓transport number of
electroactive species

34. Change metal ions in the sample to
the metal-ion complexes with
different electrochemical properties
Functions
Determine the
useable potential
Maintain constant of range of
the activity polarographic &
coefficients and the voltammetric
diffusion coefficients measurement.

35. Example of supporting electrolyte
Acids HCl, HNO3, H2SO4, H3PO4,
Citric acid
Bases NaOH, KOH, TBAOH, NH4OH
Buffers Citrate, Tartate, Acetate,
Phosphate, Borate
Non- Alcohols, Acetonitrile, DMF,
aqueous DMSO-containing dissolved
Solvents salts for conductivity

36. Thank you!!