Chapter 25: Q. 7 (page 686)
What is the purpose of the electrodeposition step in stripping analysis?
The purpose of electrodeposition step in stripping analysis is to deposit analyte on the mercury film on working electrode.
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A new method for determining ultrasmall () volumes by anodic stripping voltammetry has been proposed (W. R. Vandaveer and I. Fritsch, Anal. Chem.). In this method, a metal is exhaustively deposited from the small volume to be measured onto an electrode, from which it is later stripped. The solution volume is related to the total charge required to strip the metal by
where is the number of moles of electrons per mole of analyte, is the faraday, and is the molar concentration of the metal ion before electrolysis.
() Beginning with Faradayโs law (see Equation ), derive the above equation for .
() In one experiment, the metal deposited was from a solution that was in . The solution was electrolyzed for min at a potential of versus a gold top layer as a pseudo reference. A tubular nano band electrode was used. The silver was then anodically stripped off the electrode using a linear-sweep rate of . The following table represents idealized anodic stripping results. By integration, determine the total charge required to strip the silver from the tubular electrode. You can do a manual Simpsonโs rule integration or do the integration with Excel From the charge, determine the volume of the solution from which the silver was deposited.
() Suggest experiments to show whether all the was reduced to in the deposition step.
() Would it matter if the droplet were not a hemisphere? Why or why not?
() Describe an alternative method against which you might test the proposed method.
Distinguish between (a) voltammetry and amperometry, (b) linear-scan voltammetry and pulse voltammetry, (c) differential-pulse voltammetry and square-wave voltammetry, (d) an RDE and a ringdisk electrode, (e) faradaic impedance and double-layer capacitance, (f) a limiting current and a diffusion current, (g) laminar flow and turbulent flow, (h) the standard electrode potential and the half-wave potential for a reversible reaction at a working electrode, (i) normal stripping methods and adsorptive stripping methods.
A solution containing Cd21 was analyzed voltammetrically using the standard addition method. Twenty-
five milliliters of the deaerated solution, which was 1 M in HNO3, produced a net limiting current of 1.41 ฮผA
at a rotating mercury film working electrode at a potential of 20.85 V (versus SCE). Following addition of
5.00 mL of a 2.50 3 1023M standard Cd21 solution, the resulting solution produced a current of 4.93 ฮผA.
Calculate the concentration of Cd21 in the sample.
What is the purpose of the electrodeposition step in stripping analysis?
Why is it necessary to buffer solutions in organic voltammetry?
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