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Chapter 17: Q38P (page 431)

Peak current (IP)and scan rate (v) are listed for cyclic voltammetry of the reversible reaction Fe( II ) Fe(III ) of a water-soluble ferrocene derivative in 0.1MNaCLIf a graph of IPversusvgives a straight line, then the reaction is diffusion controlled. Prepare such a graph and use it to find the diffusion coefficient of the reactant from Equation17 - 21for this one-electron oxidation. The area of the working electrode is0.0201cm2, and the concentration of reactant is 1.00mM.

Short Answer

Expert verified

The graph between peak current and voltage for the given reaction has to be sketched.

Step by step solution

01

Define reversible reaction

In a reversible reaction, the peak current of first cycle is relative to strength of analyte and square root of the sweep rate

IPc=(2.69×108)n32ACD0.5v0.5

is the number of electrons

A is the area of the electrode(m2)

C is the concentration (mol/L)

D is diffusion coefficient of electroactive species (m2/s)

v is sweep rate ( V/ s )

02

Determine the graph between peak current and voltage for the given reaction.

TheformulaforIPis:IP=(2.69.108).n32.A.C.D.12.V12So,theslopeisequaltoIP/v12.Thediffusioncoefficientis:D=slope2(2.69.108)2.13.(0.0201.10-4m2)2.(1.10-3M)2D=7.83.10-10m2/s

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Most popular questions from this chapter

Chlorine has been used for decades to disinfect drinking water. An undesirable side effect of this treatment is reaction with organic impurities to create organochlorine compounds, some of which could be toxic. Monitoring total organic halide (designated TOX) is required for many water providers. A standard procedure for TOX is to pass water through activated charcoal, which adsorbs organic compounds. Then the charcoal is combusted to liberate hydrogen halides:

Organichalide(RX)→o2/800°CCO2+H2O+HX

HX is absorbed into aqueous solution and measured by coulometric titration with a silver anode:

X-(aq)+Ag(s)→AgX(s)+e-

When 1.00 L of drinking water was analyzed, a current of 4.23 mA was required for 387 s. A blank prepared by oxidizing charcoal required 6 s at 4.23 mA. Express the TOX of the drinking water as μmol halogen/L. If all halogen is chlorine, express the TOX as μgCI/L.

17-19. In the Figure, 17-11, 2.00nmol fructose was introduced at the time of the arrow. How many electrons are lost in the oxidation of one molecule of fructose? Compare the theoretical number of coulombs with the observed number of coulombs for complete oxidation of the sample.

Measuring the size of a microelectrode by cyclic voltammetry.

(a) Redox chemistry for ferrocyanide in Figure 17-32 was given at the beginning of Section 17-5. Write the analyte half-reaction that occurs at the upper plateau near 0.4 Vand at the lower plateau near 0 V(versus S.C.E.).

(b) The limiting current Ilimit, which is the difference between the upper and lower plateaus, is related to the radius of the disk-shaped electrode (r)and the diffusion coefficient (D)and bulk concentration (C)of the analyte:

Ilimit4nFDCr

Where nis the number of electrons in the half-reaction and F is the Faraday constant. In this equation, the units of concentration should be mol/m3to be consistent with the other quantities in SI units. The diffusion coefficient for ferrocyanide cited in the reference for Figure 17 - 32is 9.2×10-10m/sin water at25°C. Calculate the radius of the microelectrode.

(a) At what cathode potential will Sb(s)deposition commence from 0.010MSbO+solution at pH 0.00? Express this potential versus S.H.E. and versusAg|AgCI. (Disregard overpotential, about which you have no information.)

SbO++2H++3e-→Sb(s)+H2OE°=0.208V

(b) What percentage of0.10MCu2+could be reduced electrolytically to Cu(s)before0.010MSbO+in the same solution begins to be reduced at pH 0.00?

Ions that react with Ag+can be determined electrogravimetrically by deposition on a silver working anode:

Ag(s)+X-→AgX(s)+e-

(a) What will be the final mass of a silver anode used to electrolyze 75.00 mL of 0.02380 M KSCN if the initial mass of the anode is 12.4638 g?

(b) At what electrolysis voltage (versus S.C.E.) will AgBr(s) be deposited from 0.10M Br? (Consider negligible current flow, so that there is no ohmic potential, concentration polarization, or overpotential.)

(c) Is it theoretically possible to separate 99.99% of0.10M Klfrom0.10MKBr by controlled-potential electrolysis?
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