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Chapter 17: Q39P (page 431)

What are the advantages of using a microelectrode for

voltametric measurements?

Short Answer

Expert verified

The benefits of microelectrodes in voltammetry techniques has been explained.

Step by step solution

01

Define voltammetry

In the electrochemical reactions the relation between current and voltage is noted and this technique is called voltammetry. A graph which represents current Vs voltage is called voltammogram.

02

Determine the benefits of microelectrodes in voltammetry techniques

  • Microelectrodes can be placed in small places and due to less ohmic loss which is handy in nonaqueous solutions.
  • Because of its small capacitance, it allows fast scanning of voltages which allows to the analysis of unstable species.
  • It also increases the analyte sensitivity due to low capacitance which provides low current.

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Most popular questions from this chapter

Chemical oxygen demand by coulonetry. An electrochemical device incorporating photooxidation on a \({\rm{Ti}}{{\rm{O}}_2}\) surface could replace refluxing with \({{\rm{C}}_2}{\rm{O}}_7^{2 - }\) to measure chemical oxygen demand (Box 16-2). The diagram shows a working electrode beld at \( + 0.30\;{\rm{V}}\) versus \({\rm{Ag}}\mid {\rm{AgCl}}\) and coated with nanoparticles of 'TiO . Wltraviolet2inradiation generates electrons and holes in \({{\rm{T}}_1}{{\rm{O}}_2}\). Holes oxidize

organic matter at the surface. Electrons reduce \({{\rm{H}}_2}{\rm{O}}\) at the auxiliary electrode in a compartment connected to the working compartment by a salt bridge. The sample compartment is only 0.18 mm thick with a volume of \(13.5\mu \,{\rm{L}}\). It requires \(\~1\;\,{\rm{min}}\) for all organic matter to diffuse to the \({\rm{Ti}}{{\rm{O}}_2}\) surface and be exhaustively oxidized.

Left: Working electrode. Fight Photocument response for sample and blank Both solutions contain \(2{\rm{M}}\,{\rm{NaNO}}\). (Dst from H zhso, D. fisng. 5 . zhang K. Cutteral, and R. Jshn, "Development of a Drect Fhotselectrocherrical Method for Deterrination of Gherrical Ouygen Demand," And. Chan. 2004, 76 155.)

The blank curve in the graph shows the response when the sample compartment contains just electrolyte. Before inradiation, no current is observed. Ultraviolet radiation causes a spike in the current, followed by a decrease to a steady level near \(40\mu \). This current arises from oxidation of water at the \({\rm{Ti}}{{\rm{O}}_2}\)sufface under ultraviolet exposure. The upper curve sbows the same experiment, but with wastewater in the sample compartment. The increased current arises from oxidation of organic matter. When the organic matter is consumed, the cument decreases to the blank level. The area between the two curves tells us how many electrons flow from oxidation of organic matter in the sample.

  1. Balance the oxidation half-reaction that occurs in this cell:

\({{\rm{C}}_e}{{\rm{H}}_k}{{\rm{O}}_a}\;{{\rm{N}}_s}{{\rm{X}}_x} + {\rm{A}}{{\rm{H}}_2}{\rm{O}} \to {\rm{BC}}{{\rm{O}}_2} + {\rm{CX}} + {\rm{DN}}{{\rm{H}}_3} + {\rm{E}}{{\rm{H}}^ + } + {\rm{F}}{{\rm{e}}^ - }\)

where X is any halogen. Express the stoichiometry coefficients A, B, C, D, E, and F in terms of c, h, o, n, and x.

  1. How many molecules of \({{\rm{O}}_2}\)are required to balance the halfreaction in part (a) by reduction of oxygen (\({{\rm{O}}_2} + 4{{\rm{H}}^ + } + 4{{\rm{e}}^ - } \to 2{{\rm{H}}_2}{\rm{O}}\))?
  2. The area between the two curves in the graph is \(\int_0^\infty {({I_{{\rm{sample }}}}} - {I_{blank}})dt = 9.43\,{\rm{mC}}{\rm{.}}\) This is the number of electrons liberated by complete oxidation of the sample. How many moles of \({{\rm{O}}_2}\) would be required for the same oxidation?
  3. Chemical oxygen demand (COD) is expressed as mg of \({{\rm{O}}_2}\) required to oxidize 1 L of sample. Find the COD for this sample.
  4. If the only caidizable substance in the sample were \({{\rm{C}}_9}{{\rm{H}}_6}{\rm{N}}{{\rm{O}}_2}{\rm{CIB}}{{\rm{r}}_2}\). what is its concentration in molL?

Consider the following electrolysis reactions.

Cathode:H2O(l)+e-⇌12H2(g,1.0bar)+OH-(aq,0.10M)

Anode:Br-(aq,0.10M)⇌12Br2(l)+e-

  1. Calculate the voltage needed to drive the net reaction if current is negligible.
  2. Suppose that the cell has a resistance of2.0Ω and a current of 100 mA. How much voltage is needed to overcome the cell resistance? This is the ohmic potential.
  3. Suppose that the anode reaction has an overpotential of 0.20 V and that the cathode overpotential is 0.40 V. What voltage is needed to overcome these effects combined with those of parts (a) and (b)?
  4. Suppose that concentration polarization occurs [OH-]s. at the cathode surface increases to 1.0 M and[Br-]s at the anode surface decreases to 0.010 M. What voltage is needed to overcome these effects combined with those of (b) and (c)?

The cyclic voltammogram of the antibiotic chloramphenicol (abbreviated) is shown here. The first cathodic scan goes from 0 to -1.0 V. The first cathodic wave, , is from the reaction RNO2+4e-+4H+→RNHOH+H2O. Peak B in the reverse anodic scan could be assigned to RNHOH→RNO+2H++2e-. In the second cathodic scan from +0.9 to -0.4 V, the new peak C appears. Write a reaction for peak C and explain why peak C was not seen in the initial scan.


Cyclic voltammogram of 3.7 ×10-4 chloramphenicol in 0.1 M acetate buffer, pH 4.62. The voltage of the carbon paste working electrode was scanned at a rate of 350 mV/s. [Data from P. T. Kissinger and W. R. Heineman, “Cyclic Voltammetry,” J. Chem. Ed. 1983, 60, 702.]

What cathode potential (versus S.H.E.) is required to reduce 99.99%of cd(II) from a solution containing 0.10Mcd (II) in 1,0M ammonia if there is negligible current? Consider the following reactions and assume that nearly all (II) is in the form Cd(NH3)42+

localid="1663647104121" Cd2++4NH3⇌Cd(NH3)42+β4=3.6×106Cd2++2e-⇌Cd(s)E°=-.402V

A monolayer (single layer of atoms) of Cuon the (100) crystal face shown in the margin has1.53×1015atoms/cm2=2.54×10-9mol/cm2. What current can deposit one layer of Cuatoms on1cm2in 1 s?
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