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Chapter 17: Q25P (page 429)

What is a Clark electrode, and how does it work?

Short Answer

Expert verified

The process of Clark electrode has to be explained.

Step by step solution

01

Define Clark electrode

The Clark electrode is an electrode that allows amper metric measurement of dissolved oxygen activity. The electrode has glass body with a 5-mm opening at the base. Inside this opening is a 10 to 10 to 40 - mm long plug of silicone rubber, which is permeable to O2. Oxygen diffuses into the electrode through the rubber and is reduced at the Au tip on the Pt wire, held at -0.75V with respect to the AgAgCreference electrode. A Clark electrode is calibrated by placing it in solutions of knownO2concentration, and a graph of current versus OO2.

02

Explain the process of clark electrode.

  • By reducing oxygen to water on platinum electrode at -0.75V voltage of with respect to silver-silver chloride.
  • Silicone rubber of size10μmto40μmto permeable to oxygen is filled on body of platinum electrode.
  • The concentration of oxygen is proportional to current. The electrode in known oxygen concentration should be calibrated.

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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?

The standard free energy change for the formation of H2(g)=12O2(g) from H2O(l) is ∆G°=+237.13KJ The reactions are

cathode:2H2O+2e-⇌H2(g)+20H-Anode:H2O⇌12O2(g)+2H++2e-

Calculate the standard voltageE°needed to decompose water into its elements by electrolysis. What does the word standard mean in this question?

Consider the cyclic voltammogram of the Co3+compoundrole="math" localid="1663646447735" Co(B9C2H11)2- . Suggest a chemical reaction to account for each wave. Are the reactions reversible? How many electrons are involved in each step? Sketch the sampled current and square wave polarograms expected for this compound.

Cyclic voltammogramofrole="math" localid="1663646461802" Co(B9C2H11)2- . [Data from W. E. Geiger, Jr., W. L. Bowden, and N. El Murr, "An Electrochemical Study of the Protonation Site of the Cobaltocene Anion and of Cyclopentadienylcobalt(I) Dicarbollides," Inorg. Chem. 1979,18,2358.]

Explain how amperometric end-point detection in Figure17-9 operates.

Fundamentals of Electrolysis

17 - 6.The cell in Figure 17 - 4 is:

Cu|1.0MCuSO4(aq)|KCL(aq,3M)|AgCI(s)|Ag(s)

Write half-reactions for this cell. Neglecting activity coefficients and the junction potential betweenCuSO4(aq)and KCI(aq), predict the equilibrium (zero-current) voltage expected when the Lugging capillary contacts the electrode. For this purpose, suppose that the reference electrode potential is 0.197Vvs. S.H.E. Why is the observed equilibrium potential+109mV, not the value you calculated?

How would the over potentials change if>1.000Vwere imposed by the

Potentiostat?
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