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CHE3704 ANALYTICAL CHEMISTRY 2021 TUTORIAL LETTER 201
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CHE3704/201/3/2021Tutorial Letter 201/3/2021
Analytical Chemistry III (Theory)
CHE3704
Semesters 1 & 2
Department of Chemistry
IMPORTANT INFORMATION
Please register on myUnisa, activate your myLife e-mail account and
make sure that you have regular access to the myUnisa module
website, CHE3704-2021-S1/S2, as well as your group website
BARCODE
, ASSIGNMENT 01 SOLUTIONS
Question 1 Solutions
(a) Differences between the following voltammetric terms given:
(i) Voltammetry is an analytical technique that is based on measuring the current that develops at a
small electrode as the applied potential (voltage) is varied (or, the techniques and methodology of
measuring current as a function of applied potential); while amperometry is a technique in which
the limiting current is measured at a constant potential (or, the techniques and methodology of
determining a concentration as a function of current).
(ii) Differential pulse voltammetry is a form of voltammetry that uses the differential-pulse
waveform as voltage versus time excitation signals (or, a form of voltammetry in which a linear
potential ramp of dE/dt is applied to the working electrode, superimposed on which is a
succession of pulses); while square wave voltammetry is a form of voltammetry with square-
wave waveform acting as voltage versus time excitation signals (or, a form of voltammetry in
which the potential waveform applied to the working electrode is a square wave), as depicted in
the figures below.
Differential pulse Square wave
voltammetry voltammetry
(iii)Limiting current is a current that is independent of applied potential and limited by the rate at
which a reactant is brought to the surface of the electrode by migration, convection, and/or
diffusion; while diffusion current is a limiting current when analyte transport is solely by
diffusion.
(iv) Standard electrode potential is the potential, denoted by E0 (relative to the standard hydrogen
electrode, SHE), of a half-reaction written as a reduction when the activities of all reactants and
products are unity (or, an electrode potential measured at standard temperature and pressure,
where all products and reagents are present at unit activity); while half-wave potential, denoted by
E1/2, is the potential versus a reference electrode at which the current of a voltametric wave is one
half the limiting current (or, an electrode potential from polarography that is characteristic of the
analyte), and it is given mathematically as
E1/2 = – ,
2
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