1) Write a short note on standard or reference electrode.
There are two types of electrodes:
a. Primary reference electrode: This type of electrode is also known as Standard
Hydrogen Electrode. To form this electrode pure hydrogen gas under one
atmospheric pressure is bubbled around platinized platinum which is immersed in
a solution containing H+ ions at unit activity. By maintaining a
constant pressure of hydrogen gas this electrode is used to determine the
activity of hydrogen ions. The hydrogen electrode is used in fundamental
studies. It is also used for some non-aqueous solutions.
b. Secondary reference electrode: These electrodes are extremely stable and are
prepared easily. The electrode potential of such does not vary with
temperature. A common example of this is a Calomel Electrode. The potential of
the calomel electrode depends upon the concentration of the potassium chloride
solution used in the calomel electrode. It is used in the measurement of pH,
cyclic voltammetry and general aqueous electrochemistry. This electrode
contains Mercury which is hazardous for health and hence silver chloride is
also used as secondary reference electrode. Both these electrodes work in the
same way.
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2) Explain the classification of electrodes.
Electrodes are classified in four groups:
a. Amalgam electrode: When the pure metals are too active to use them in aqueous
solution then they are used in the form of mercury amalgams and hence such
electrodes are known as amalgam electrode. These are constructed by dipping
amalgam of the desired metal in solution of its salt.
b. Metal-metal ion electrode: In such type of electrode the metal is in
equilibrium with its ion in solution. The electrode consists of a strip of
metal dipped in solution containing its ion.
c. Metal-Insoluble salt electrode: In such electrodes the metal is in contact
with one of its sparingly soluble salt and with the solution containing the ion
present in the salt other than the metal.
d. Gas electrode: To construct such electrodes special arrangement is required.
In this case generally a platinum foil is immersed in the solution and then the
gas is passed through it so that the foil is saturated with adsorbed gas. The
metal foil is used to establish equilibrium between the gas and the ions in the
solution and also the electric contact.
3) What are the advantages and disadvantages of a glass electrode?
Advantages:
a. It is free from poising.
b. It is easy to handle.
c. It can be used for measurement even if the volume of solution is small.
d. Glass electrode can be used in presence of proteins and other substance that
interfere with other electrodes.
e. It can be used with solutions having a pH 0f 2 to 10. In some cases like
lithium glasses it can be used for solutions having a pH of about 14
Disadvantages:
a. It should be handled carefully as it is fragile and is made up of glass.
b. It loses its sensitivity if kept dried or if stored and thus 12 hours prior
to usage it should be kept immersed in distilled water.
c. It cannot be used in pure ethyl alcohol, gelatine and acetic acid.
d. An ordinary potentiometer cannot be used for the measurement of e.m.f as the
glass electrode membrane has high resistance. Always an electronic
potentiometer should be preferred.
4) Write a short note on electrolytic conduction and the various factors
affecting it.
Conductors are the substance that allows the electricity to pass through them. A
conductor which undergoes decomposition when current is passed through them is
known as electrolytic conductors or electrolytes. For example: solutions of
acids, bases and salts in water. Here movement of ions causes the electricity
to flow.
Electrolytes can be further classified as strong electrolytes like HCl, HNO3,
H2SO4 , NaOH, KOH etc. and weak electrolytes like CH3COOH,
HCN, H3PO4, NH4OH etc. Strong electrolytes
dissociate completely in an aqueous solution and produces electric current
where as weak electrolytes does not dissociate completely and hence produces
electric current to a small extent.
Factors affecting electrolytic conduction are:
a. Temperature: With an increase in temperature the electrolytic conduction
increases.
b. Nature of solvent: Generally the electrolyte ionizes in polar solvent and
hence electrolytic conduction is directly proportional to the polarity of the
solvent.
c. Nature of the electrolyte: A strong electrolyte dissociates completely and
thus conducts electricity to a greater extent where as weak electrolytes
conduct electricity to a small extent.
d. Concentration of the solution: On dilution the conduction increases. This
means that for the solution with higher concentration, conduction is less. This
is because at higher concentration the ionisation is less in a weak electrolyte
and interionic attractions are high in strong electrolyte. However with
dilution the conduction increases.
5) Write a short note on electrochemical series and give its applications.
The electrodes are arranged in a series according to their increasing values of
standard reduction potential. This series is known as electrochemical series.
This series also includes the activity series of metals as the relative
activity of metals can be obtained by comparing their oxidation potentials.
Its applications are:
a. To compare the relative activities of metals: A metal with greater oxidation
potential can displace a metal with lower oxidation potential from their salt
solution.
b. Used to calculate the standard EMF of any electrochemical cell: The equation
is given as:
Standard EMF of the cell = [Standard oxidation potential of the oxidation half
reaction] + [Standard reduction potential of the reduction half reaction]
c. To compare the relative oxidizing and reducing power: We know that the
positive sign represent the reduction potential. Thus greater is the reduction
potential, easily can it be reduced.
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