A new method for determining ultrasmall (nL) volumes hy anodic strippingvoltammetrv has

Chapter 25, Problem 25-17

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A new method for determining ultrasmall (nL) volumes hy anodic strippingvoltammetrv has been proposed (W. R. Vandaveer and I. Fritsch, Anal. Chern.,2002,74,3575). In this mcthod, a metal is exhaustively deposited from the smallvolume to be measured onto an electrode, from which it is later stripped. The solutionvolume V, is related to the total charge Q required to strip the metal byV=~, nFCwhere n is the numher of moles of electrons per mole of analyte, F is the faraday,and C is the molar concentration of the metal ion hefore electrolysis.(a) Beginning with Faraday's law (see Equation 22-8), derive the ahove equationfor v.,.(b) In one experiment, the metal deposited was Ag(s) from a solution that was8.00 mM in AgN03 The solution was electrolyzed for 30 min at a potentialof -0.700 V versus a gold top layer as a pseudoreference. A tuhular nanobandelectrode was used. The silver was then anodically stripped off theelectrode using a linear sweep rate of 0.10 Vis.The following table representsidealized anodic stripping results. By integration, determine.the totalcharge required to strip the silver from the tubular electrode. Y~u can do amanual Simpson's rule integration or do the integration with ExeeT.49 Fromthe charge, determine the volume of the solution from which the silver wasdeposited.Potential, V Current, nA Potential, V Current, nA-0.50 0.000 -0.123 - 1.10-0.45 -0.02 -0.\0 -0.80-0.40 -0.001 -0.\15 -\'OO-0.30 -0.\0 -0.09 -0.65-0.25 -0.20 -0.08 -0.52-0.22 -0.30 -0.065 -0.37-0.20 -0.44 -0.05 -0.22-0.18 -0.67 -0.D25 -0.12-0175 -0.80 0.00 -0.05-0.168 -1.00 0.05 -0.03-0.16 - 1.18 0.\0 -OJJ2-0.15 1.34 0.15 -O.lX15-0.135 -l.28(c) Suggest experiments to show whether all the Ag' was reduced to Ag(s) inthe deposition step.(d) Would it matter if the droplet were not a hemisphere" Why or why not 0(c) Describe an alternative method against which you might test the proposedmethod.