Electrochemistry is the study of chemical reactions caused by electricity or that produce electricity. An electrochemical cell converts chemical energy into electrical energy and vice versa. There are two main types of electrochemical cells: (1) Galvanic/voltaic cells where a spontaneous redox reaction produces electricity, and (2) electrolytic cells where electricity drives a non-spontaneous reaction. Conductometric titration measures the change in conductivity during a titration reaction and can be used to determine the endpoint. The conductivity changes differently based on whether the acid and base are strong or weak.
2. ELECTRO CHEMISTRY
Introduction to Electrochemistry
Electrochemistry is the study of electricity
production from energy released during
spontaneous chemical reactions and how the
electrical energy usage brings about non-
spontaneous chemical transformations. A large
number of metals such as sodium and
magnesium, compounds like sodium oxide, and
gases like chlorine and fluorine are produced by
electrochemical processes. Batteries and fuel
cells convert chemical energy into electrical
energy and are used in large scale and
devices. Let’s get introduced to some important
terms related to an electrochemical cell
3. Oxidation and Reduction
• During oxidation, a loss of electrons takes place
whereas during reduction, a gain of electrons is
happening. Both oxidation and reduction reactions
take place simultaneously in a redox reaction.
Direct redox reactions involve a redox reaction in
the same vessel and chemical energy gets
converted to heat energy. During indirect redox
reactions, oxidation and reduction takes place in
different vessels and chemical energy is converted
into electrical energy and the device where this
takes place is called an electrochemical cell.
4. ELECTRO CHEMICAL CELL
An electrochemical cell is a device which is capable of either producing an
electric current due to chemical action or of producing chemical action due to
the passage of electricity.
Types of Electrochemical Cell
• There are two types of electrochemical cells, named as follows:
• Voltaic Cells/Galvanic cell: In voltaic cells, the chemical energy of a
spontaneous redox reaction is converted into electrical energy. These are
also called galvanic cells. The electrical energy produced by such batteries
can be used for powering cell phones, radios, and other devices.
• Electrolytic Cells: In electrolytic cells, electrical energy is needed to carry
out a non-spontaneous chemical reaction. When we charge a cell phone
battery, it’s like running an electrolytic cell
6. VOLTAIC CELL
• Voltaic Cell: It consists of a half cell where oxidation takes place and
it is known as oxidation half-cell; the other half-cell where reduction
takes place is called reduction half-cell. Two half cells must be
connected to build a voltaic cell. Oxidation takes place at negatively
charged anode and reduction takes place at positively charged cathode.
There will be a transfer of electrons taking place from anode to
cathode when electric current flows in the opposite direction. An
electrochemical cell also consists of an electrode which is prepared by
dipping the metal plate into the electrolytic solution of its soluble salt.
A salt bridge is a U shaped tube consisting of an inert electrolyte in
agar-agar and gelatine. It maintains electrical neutrality and also
allows the flow of electric current by completing the electric circuit.
8. Electrolytic Cell
• Electrolytic Cell
• The electrolytic cell converts electrical energy to chemical energy. Here the electrodes are dipped
in an electrolytic solution containing cations and anions. On supplying current the ions move
towards electrodes of opposite polarity and simultaneous reduction and oxidation take place.
• For example, in the electrolysis of molten sodium chloride, sodium chloride is melted (above
801oC), two electrodes are inserted into the melt, and an electric current is passed through the
molten salt. The chemical reaction that takes place at the electrodes are:
• ● Sodium-ion migrates to the cathode, where sodium ion gains one electron and reduce to sodium
metal.
• Na+ + e–→ Na
• Chloride ions migrate towards the anode where it loses one electron and gets oxidised to chlorine
gas.
• Cl–→1/2 Cl2 + e–
• The overall reaction is the breakdown of sodium chloride into its elements
• 2NaCl→ 2Na(s) + Cl2(g)
•
10. Conductometric titration of strong acid vs strong
base( HCl vs NaOH)
When a strong acid such as HCl taken in a beaker is titrated with a strong base such as
NaOH, the fast-moving hydrogen ions are replaced by slow-moving sodium ions and the
conductance decreases gradually up to the equivalent point. Let’s see the reaction.
HCl is a strong acid and hence, the conductance of the HCl acid solution is very high
initially due to the presence of fast-moving H+ ions. When NaOH solution is added
gradually, the fast-moving H+ ions are replaced by slow-moving Na+ ions, and thus, the
conductance of the solution keeps on declining till the endpoint is achieved.
After the endpoint, On adding NaOH solution librates fast-moving OH- ions to the
solution, and hence the conductance increases gradually increases. The conductometric
titration curve or the graph of HCl vs NaOH is shown below.
12. Conductometric titration of weak acid and strong base(CH3COOH Vs
NaOH)
Initially, the conductance of acetic acid solution is low because it is a weak acid and
weakly dissociated. When we add NaOH solution from a burette, there is a slight
decrease in the conductance of the solution which is due to the substitution of free H+
ions by slow-moving Na+ ions. On further addition of NaOH solution, the conductance
of solution increases slightly due to formation of highly ionized compound CH3COONa,
till endpoint. After the endpoint, the addition of NaOH further, there is an increase in
the conductances of solution sharply which is due to free OH–ions. The conductometric
titration graph of CH3COOH vs NaOH is shown below.
14. Conductometric titration of strong acid and weak base
( HCl vs NH4OH)
In the beginning, the conductance of the HCl solution is very high due to
the liberation of fast-moving H+ ions. But, when a weak base such as
NH4OH is added from the burette, the fast-moving H+ ions are replaced by
slow-moving NH4+ ions. Therefore, the conductance decreases until the
endpoint is reached. After the endpoint, when further NH4OH is added to
the solution, the conductance of the solution does not change because
NH4OH is a weak base. The conductometric titration graph of HCl vs
NH4OH is shown below.
