DOCSLIB.ORG

Field Measurement of Oxidation-Reduction Potential (ORP)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Field Measurement of Oxidation-Reduction Potential (ORP) COPY COPY Revision History The top row of this table shows the most recent changes to this controlled document. For previous revision history information, archived versions of this document are maintained by the SESD Document Control Coordinator on the SESD local area network (LAN). History Effective Date SESDPROC-113-R2, Field Measurement of Oxidation-Reduction April 26, 2017 Potential (ORP), replaces SESDPROC-013-R1 General: Corrected any typographical, grammatical, and/or editorial errors. Title Page: Changed the EIB Chief from Danny France to the Field Services Branch Chief John Deatrick, and the Field Quality Manager from Bobby Lewis to Hunter Johnson. Section 2.2: Figure 6 modified for clarity. Section 3.3: Use of overtopping cell described consistent with current practice. SESDPROC-113-R1, Field Measurement of Oxidation-Reduction January 29, 2013 Potential (ORP), replaces SESDPROC-013-R0 SESDPROC-113-R0, Field Measurement of Oxidation-Reduction August 7, 2009 Potential (ORP), Original Issue SESD Operating Procedure Page 2 of 22 SESDPROC-113-R2 Field Measurement of ORP Field Measurement of ORP(113)_AF.R2 Effective Date: April 26, 2017 COPY TABLE OF CONTENTS 1 General Information ............................................................................................................ 4 1.1 Purpose........................................................................................................................... 4 1.2 Scope/Application ......................................................................................................... 4 1.3 Documentation/Verification ......................................................................................... 4 1.4 References ...................................................................................................................... 4 1.5 General Considerations ................................................................................................ 5 1.5.1 Safety .......................................................................................................................... 5 1.5.2 Records ....................................................................................................................... 6 1.5.3 Shipping ...................................................................................................................... 6 2 Background ........................................................................................................................... 7 2.1 General ........................................................................................................................... 7 2.2 Instrumentation............................................................................................................. 8 2.3 Redox Chemistry ......................................................................................................... 14 2.4 Applications ................................................................................................................. 15 2.5 Limitations ................................................................................................................... 16 3 Methodology ........................................................................................................................ 18 3.1 Standard Solutions ...................................................................................................... 18 3.2 Verification and Calibration ...................................................................................... 19 3.3 Measurement ............................................................................................................... 20 3.4 Reporting ..................................................................................................................... 21 SESD Operating Procedure Page 3 of 22 SESDPROC-113-R2 Field Measurement of ORP Field Measurement of ORP(113)_AF.R2 Effective Date: April 26, 2017 COPY 1 General Information 1.1 Purpose This document describes procedures, methods and considerations to be used and observed when conducting field Oxidation-Reduction Potential (ORP) measurements in aqueous environmental media, including groundwater, surface water and certain wastewater. The measurement of soil ORP is a non-standard measurement and procedures should be developed on a project-specific basis. 1.2 Scope/Application This document describes procedures generic to all ORP measurement methods to be used by Science and Ecosystem Support Division (SESD) field personnel when collecting and handling samples in the field. On the occasion SESD personnel determine that any of the procedures described in this section are inappropriate, inadequate or impractical and that another procedure must be used to obtain an ORP measurement, the variant procedure will be documented in the field logbook, along with a description of the circumstances requiring its use. Mention of trade names or commercial products in this operating procedure does not constitute endorsement or recommendation for use. 1.3 Documentation/Verification This procedure was prepared by persons deemed technically competent by SESD management, based on their knowledge, skills and abilities and has been tested in practice and reviewed in print by a subject matter expert. The official copy of this procedure resides on the SESD local area network (LAN). The Document Control Coordinator (DCC) is responsible for ensuring the most recent version of the procedure is placed on the SESD LAN and for maintaining records of review conducted prior to its issuance. 1.4 References Faulkner, S.P., W.H. Patrick, Jr., and R.P. Gambrell. 1989. Field techniques for measuring wetland soil parameters. Soil Sci. Soc. Am. J. 53:883-890. Megonigal, J.P., W.H. Patrick, Jr., and S.P. Faulkner. 1993. Wetland identification in seasonally flooded forest soils: soil morphology and redox dynamics. Soil Sci. Soc. Am. J. 57:140-149. D.K. Nordstrom and F.D. Wilde. 2005. National Field Manual, Chapter A6, Section 6.5: Reduction Oxidation Potential (Electrode Method). USGS. Pankow, J.E. 1991. Aquatic chemistry concepts. Lewis Publishers, Inc. Cheleas, Michigan. USA. Pruitt, B.A. 2001. Hydrologic and soil conditions across hydrogeomorphic settings. Dissertation. The University of Georgia, Athens, GA. USA. SESD Operating Procedure Page 4 of 22 SESDPROC-113-R2 Field Measurement of ORP Field Measurement of ORP(113)_AF.R2 Effective Date: April 26, 2017 COPY Soil Survey Staff. 1998. Keys to soil taxonomy, 8th Edition. United States Department of Agriculture, Natural Resources Conservation Service, Washington, DC. USA. Standard Methods. 1992. Standard Methods for the Examination of Water and Wastewater, 18th Edition. Prepared and published jointly by: American Public Health Association, American Water Works Association, Water Environment Federation. American Public Health Association, Washington, DC. USA. Stumm, W. and J.J. Morgan. 1981. Aquatic chemistry: an introduction emphasizing chemical equilibra in natural waters, 2nd Ed. John Wiley & Sons, New York. USA. USEPA. 2001. Environmental Investigations Standard Operating Procedures and Quality Assurance Manual. Region 4 Science and Ecosystem Support Division, Athens, GA. USEPA. 2007. Safety, Health and Environmental Management Program Procedures and Policy Manual. Science and Ecosystem Support Division, Region 4, Athens, GA. Wikipedia entry. Reduction Potential. http://en.wikipedia.org/wiki/Reduction_potential. Retrieved April 2, 2009. 1.5 General Considerations 1.5.1 Safety Proper safety precautions must be observed when verifying or calibrating instruments for measurement of Oxidation-Reduction Potential. Refer to the SESD Safety, Health and Environmental Management Program Procedures and Policy Manual (most recent version) and any pertinent site-specific Health and Safety Plans (HASP) for guidelines on safety precautions. These guidelines should be used to complement the judgment of an experienced professional. Reagents commonly used in the preparation of ORP calibration standards are toxic and require care when handling. When using this procedure, avoid exposure to these materials through the use of protective clothing, eye wear and gloves. Safety precautions when handling and preparing verification solutions should include gloves and eyewear to prevent dermal and eye contact, and a mask to avoid inhaling dust particles when handling dry materials. Vigorous flushing should be used if the reagents or solutions come in contact with skin or eyes. Following is specific information on commonly used solutions. The application of the solutions is described in detail in Section 3.1, Standard Solutions, of this procedure. • Quinhydrone (CAS# 106-34-3) is a skin and respiratory irritant and is poisonous if ingested. Safety precautions when handling quinhydrone should include gloves to prevent dermal contact and a mask to avoid inhaling dust particles when mixing dry SESD Operating Procedure Page 5 of 22 SESDPROC-113-R2 Field Measurement of ORP Field Measurement of ORP(113)_AF.R2 Effective Date: April 26, 2017 COPY material to prepare calibration standards. Vigorous flushing should be used if concentrated material comes in contact with skin or eyes. • Zobell’s solution is also an irritant and toxic if ingested. The same handling precautions apply when mixing and using Zobell’s solution as when using quinhydrone. Zobell’s reacts with acid to form harmful byproducts, including hydrocyanide gas. • Light’s solution contains ferro- and ferric-cyanide compounds
Load more

Recommended publications
  • Chapter 3: Experimental
    Chapter 3: Experimental CHAPTER 3: EXPERIMENTAL 3.1 Basic concepts of the experimental techniques In this part of the chapter, a short overview of some phrases and theoretical aspects of the experimental techniques used in this work are given. Cyclic voltammetry (CV) is the most common technique to obtain preliminary information about an electrochemical process. It is sensitive to the mechanism of deposition and therefore provides informations on structural transitions, as well as interactions between the surface and the adlayer. Chronoamperometry is very powerful method for the quantitative analysis of a nucleation process. The scanning tunneling microscopy (STM) is based on the exponential dependence of the tunneling current, flowing from one electrode onto another one, depending on the distance between electrodes. Combination of the STM with an electrochemical cell allows in-situ study of metal electrochemical phase formation. XPS is also a very powerfull technique to investigate the chemical states of adsorbates. Theoretical background of these techniques will be given in the following pages. At an electrode surface, two fundamental electrochemical processes can be distinguished: 3.1.1 Capacitive process Capacitive processes are caused by the (dis-)charge of the electrode surface as a result of a potential variation, or by an adsorption process. Capacitive current, also called "non-faradaic" or "double-layer" current, does not involve any chemical reactions (charge transfer), it only causes accumulation (or removal) of electrical charges on the electrode and in the electrolyte solution near the electrode. There is always some capacitive current flowing when the potential of an electrode is changing. In contrast to faradaic current, capacitive current can also flow at constant 28 Chapter 3: Experimental potential if the capacitance of the electrode is changing for some reason, e.g., change of electrode area, adsorption or temperature.
    [Show full text]
  • Square Wave Voltammetry
    Application Note S-7 Subject: Square Wave Voltammetry INTRODUCTION reverse pulse of the square wave occurs half way through the staircase step. The primary advantage of the pulse voltammetric techniques, such as normal pulse or differential pulse voltammetry, is their ability to discriminate against charging (capacitance) current. As a result, the pulse techniques are more sensitive to oxidation or reduction currents (faradaic currents) than conventional dc PLUS voltammetry. Differential pulse voltammetry yields peaks for faradaic currents rather than the sigmoidal waveform obtained with dc or normal pulse techniques. This results in improved resolution for multiple analyte systems and more convenient quantitation. Square wave voltammetry has received growing attention as a voltammetric technique for routine quantitative analyses. Although square wave voltammetry was E reported as long ago as 1957 by Barker1, the utility of the EQUALS technique was limited by electronic technology. Recent advances in both analog and digital electronics have made it feasible to incorporate square wave voltammetry into the PAR Model 394 Polarographic Analyzer. Square wave voltammetry can be used to perform an experiment much faster than normal and differential pulse techniques, which typically run at scan rates of 1 to 10 mV/sec. Square wave voltammetry employs scan rates TIME up to 1 V/sec or faster, allowing much faster determinations. A typical experiment requiring three minutes by normal or differential pulse techniques can be performed in a matter of seconds by square wave voltammetry. FIGURE 1: Applied excitation in square wave voltammetry. THEORY The timing and applied potential parameters for square The waveform used for square wave voltammetry is wave voltammetry are depicted in Figure 2.
    [Show full text]
  • Redox Potential Measurements M.J
    Redox Potential Measurements M.J. Vepraskas NC State University December 2002 Redox potential is an electrical measurement that shows the tendency of a soil solution to transfer electrons to or from a reference electrode. From this measurement we can estimate whether the soil is aerobic, anaerobic, and whether chemical compounds such as Fe oxides or nitrate have been chemically reduced or are present in their oxidized forms. Making these measurements requires three basic pieces of equipment: 1. Platinum electrode 2. Voltmeter 3. Reference electrode The basic set-up is shown below: Voltmeter 456 mv Soil surface Reference Pt wire electrode Fig. 1. The Pt wire is buried into the soil to be in contact with the soil solution. The reference electrode must also be in contact with the soil solution. It has a ceramic tip, which can be placed in the soil, or the electrode can be placed in a salt bridge, which is itself placed in the soil. Wires from both the Pt electrode and reference electrode are connected to the voltmeter. Pt Electrodes Platinum electrodes consist of a small piece of platinum wire that is soldered or fused to wire made another metal. Platinum conducts electrons from the soil solution to the wire to which it is attached. Platinum is used because it is assumed to be an inert metal. This means it does not give up its own electrons (does not oxidize) to the wire or soil solution. Iron containing materials such as steel will oxidize themselves and send their own electrons to the voltmeter. As a result the voltage we measure will not result solely from electrons being transferred to or from the soil.
    [Show full text]
  • Lecture Content
    EMT 518: METHODS IN ENVIROMENTAL ANALYSIS III (2 UNITS) Lecturer: Professor O. Bamgbose SYNOPSIS Electro-analytical method: Potentiometry, Reference electrode – Calomel, Ag/Agcl, indicator electrodes – 1st, 2nd and 3rd order, Metal Electrodes, membrane electrodes – glass electrode, types of liquid junction potential, solid state electrode, potentiometric titration, end point location in potentiometric titration –visual, plot of E/V, plot of derivative curves 1st and 2nd electrogravimetry, fixed potential, constant current, constant cathode potential coulometry: constant current coulometry, coulometric titration. Voltammetry: classical polarography, Description of dropping mercury electrode, condition for polarographic determination, qualitative and quantitative analysis conductance methods: description of limiting ionic conductance, conductance cell, conductomertic titration. Thermal methods: Thermogravimetry, differential thermal analysis (DTA) LECTURE CONTENT POTENTIOMETRY Is a measurement of a given chemical species in an equilibrium system by the use of an electrode, while potentiometric titration is the technique that is used for following the changes in the concentration of chemical species as function of added titrant using an electrode. In both cases a cell is needed and a cell consists of the following: (1) Reference electrode (2) Liquid junction (3) Analyte solution (4) indicator electrode. It is also possible to have a cell without liquid junction. REFERENCE ELECTRODE. In carrying out a potentiometric determination the half cell potential of one electrode must be known which should be constant, reproducible and completely insensitive to the reference electrode and must be fully polarised throughout the duration of the measurement i.e the potential of the reference electrode does not change through the whole measurement. A classical example of reference electrode is the calomel electrode.
    [Show full text]
  • Frequency and Potential Dependence of Reversible Electrocatalytic Hydrogen Interconversion by [Fefe]-Hydrogenases
    Frequency and potential dependence of reversible electrocatalytic hydrogen interconversion by [FeFe]-hydrogenases Kavita Pandeya,b, Shams T. A. Islama, Thomas Happec, and Fraser A. Armstronga,1 aInorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3QR, United Kingdom; bSchool of Solar Energy, Pandit Deendayal Petroleum University, Gandhinagar 382007, Gujarat, India; and cAG Photobiotechnologie Ruhr–Universität Bochum, 44801 Bochum, Germany Edited by Thomas E. Mallouk, The Pennsylvania State University, University Park, PA, and approved March 2, 2017 (received for review December 5, 2016) The kinetics of hydrogen oxidation and evolution by [FeFe]- CrHydA1 contains only the H cluster: in the living cell, it receives hydrogenases have been investigated by electrochemical imped- electrons from photosystem I via a small [2Fe–2S] ferredoxin ance spectroscopy—resolving factors that determine the excep- known as PetF (19). No accessory internal Fe–S clusters are tional activity of these enzymes, and introducing an unusual and present to mediate or store electrons. powerful way of analyzing their catalytic electron transport prop- For enzymes, PFE has focused entirely on net catalytic electron erties. Attached to an electrode, hydrogenases display reversible flow that is observed as direct current (DC) in voltammograms + electrocatalytic behavior close to the 2H /H2 potential, making (2, 3, 10). Use of DC cyclic voltammetry as opposed to single them paradigms for efficiency: the electrocatalytic “exchange” rate potential sweeps alone helps to distinguish rapid, steady-state (measured around zero driving force) is therefore an unusual pa- catalytic activity at different potentials from relatively slow, rameter with theoretical and practical significance. Experiments potential-dependent changes in activity that are revealed as were carried out on two [FeFe]-hydrogenases, CrHydA1 from the hysteresis (10).
    [Show full text]
  • Stationary Electrode Voltammetry and Chronoamperometry in an Alkali Metal Carbonate-Borate Melt
    AN ABSTRACT OF THE THESIS OF DARRELL GEORGE PETCOFF for the Doctor of Philosophy (Name of student) (Degree) in Analytical Chemistry presented onC (O,/97 (Major) (Date) Title: STATIONARY ELECTRODE VOLTAMMETRY AND CHRONOAMPEROMETRY IN AN ALKALI METAL CARBONATE - BORATE. MFT T Abstract approved: Redacted for Privacy- Drir. reund The electrochemistry of the lithium-potassium-sodium carbonate-borate melt was explored by voltammetry and chrono- amperometry. In support of this, a controlled-potential polarograph and associated hardware was constructed.Several different types of reference electrodes were tried before choosing a porcelain mem- brane electrode containing a silver wire immersed in a silver sulfate melt.The special porcelain compounded was used also to construct a planar gold disk electrode.The theory of stationary electrode polarography was summarized and denormalized to provide an over- all view. A new approach to the theory of the cyclic background current was also advanced. A computer program was written to facilitate data processing.In addition to providing peak potentials, currents, and n-values, the program also resolves overlapping peaks and furnishes plots of both processed and unprocessed data. Rapid-scan voltammetry was employed to explore the electro- chemical behavior of Zn, Co, Fe, Tl, Sb, As, Ni, Sn, Cd, Te, Bi, Cr, Pb, Cu, and U in the carbonate-borate melt. Most substances gave reasonably well-defined peaks with characteristic peak potentials and n-values.Metal deposition was commonly accompanied by adsorp- tion prepeaks indicative of strong adsorption, and there was also evi- dence of a preceding chemical reaction for several elements, sug- gesting decomplexation before reduction.
    [Show full text]
  • Computational Redox Potential Predictions: Applications to Inorganic and Organic Aqueous Complexes, and Complexes Adsorbed to Mineral Surfaces
    Minerals 2014, 4, 345-387; doi:10.3390/min4020345 OPEN ACCESS minerals ISSN 2075-163X www.mdpi.com/journal/minerals Review Computational Redox Potential Predictions: Applications to Inorganic and Organic Aqueous Complexes, and Complexes Adsorbed to Mineral Surfaces Krishnamoorthy Arumugam and Udo Becker * Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Avenue, 2534 C.C. Little, Ann Arbor, MI 48109-1005, USA; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-734-615-6894; Fax: +1-734-763-4690. Received: 11 February 2014; in revised form: 3 April 2014 / Accepted: 13 April 2014 / Published: 24 April 2014 Abstract: Applications of redox processes range over a number of scientific fields. This review article summarizes the theory behind the calculation of redox potentials in solution for species such as organic compounds, inorganic complexes, actinides, battery materials, and mineral surface-bound-species. Different computational approaches to predict and determine redox potentials of electron transitions are discussed along with their respective pros and cons for the prediction of redox potentials. Subsequently, recommendations are made for certain necessary computational settings required for accurate calculation of redox potentials. This article reviews the importance of computational parameters, such as basis sets, density functional theory (DFT) functionals, and relativistic approaches and the role that physicochemical processes play on the shift of redox potentials, such as hydration or spin orbit coupling, and will aid in finding suitable combinations of approaches for different chemical and geochemical applications. Identifying cost-effective and credible computational approaches is essential to benchmark redox potential calculations against experiments.
    [Show full text]
  • Microfluidic Reference Electrode for Applications
    MICROFLUIDIC REFERENCE ELECTRODES FOR APPLICATIONS IN BIOSENSING S. Safari-Mohsenabad1, P.R. Selvaganapathy1*, and M.J. Deen2# 1Mechanical Engineering, 2Electrical& Computer Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada ABSTRACT A microfluidic Silver/Silver Chloride (Ag/AgCl) reference electrode was fabricated and operated in various modes. This micro-scale reference electrode design includes all the features of the macro-scale version including, Ag/AgCl elec- trode, inner standard solution and nanoporous membrane separator in a small form factor. This miniature reference elec- trode could also be operated in modes where the liquid junction potential can be stabilized to provide a stable potential. In one such mode, the microfluidic reference electrode with a free diffusion liquid junction shows < 0.1 mV stability over a 100-hour lifespan and no sensitivity to pH and chlorine concentration of the external solution. KEYWORDS: Ag/AgCl reference electrode, free-diffusion liquid junction, microfabrication, microfluidics INTRODUCTION Reference electrodes are used in situations where electrical sensors interface with ionic solutions and are typically used to impose or measure an electric potential in a solution [1]. Reference electrodes are used in many applications including pH sensing, corrosion monitoring, environmental sensing and blood gas analysis [2]. In addition, the reference electrode has a pronounced influence on the measurement accuracy of electrochemical bio-sensors [3], bio-impedance probes [4] and biological field-effect transistors (BioFETs) [5], especially for low analyte concentrations. For example, a reference electrode is used to impose a bias voltage on the gate of a BioFET that has been functionalized with a biorecognition probe molecule such as a DNA [6].
    [Show full text]
  • "Relationships Between Oxidation-Reduction Potential
    Relationships between Oxidation-Reduction Potential, Oxidant, and pH in Drinking Water Cheryl N. James3, Rachel C. Copeland2, and Darren A. Lytle1 1U.S. Environmental Protection Agency, NRMRL, Cincinnati, OH 2University of Cincinnati, Department of Environmental Engineering, Cincinnati, OH 3University of Cincinnati, Department of Chemical Engineering, Cincinnati, OH Abstract –Oxidation and reduction (redox) reactions are very important in drinking water. Oxidation-reduction potential (ORP) measurements reflect the redox state of water. Redox measurements are not widely made by drinking water utilities in part because they are not well understood. The objective of this study was to determine the effect of oxidant type and concentration on the ORP of carbonate buffered water as a function of pH. Oxidants that were studied included: chlorine, monochloramine, potassium permanganate, chlorine dioxide, and oxygen. ORP decreased with increasing pH, regardless of the oxidant type or concentration. ORP increased rapidly with increasing oxidant dosage, particularly at lower concentrations. Differences in the redox potentials of different oxidant systems were also observed. Waters that contained chlorine and chlorine dioxide had the highest ORPs. Tests also revealed that there were inconsistencies with redox electrode measurements. In the standard Zobell reference solution, two identical redox electrodes had nearly the same reading, but in test waters the readings sometimes showed a variation as great as 217.7 mV. Key words: ORP, redox potential, redox chemistry, oxidant, drinking water 1.0 BACKGROUND 1.1 Redox Theory Oxidation-reduction (redox) reactions describe the transfer of electrons between atoms, molecules, or ions. Oxidation and reduction reactions occur simultaneously and together make up an electrochemical couple.
    [Show full text]
  • Quasi-Reference Electrodes in Confined Electrochemical Cells Can
    www.nature.com/scientificreports OPEN Quasi-reference electrodes in confned electrochemical cells can result in in situ production of Received: 13 September 2017 Accepted: 15 January 2018 metallic nanoparticles Published: xx xx xxxx Rukshan T. Perera & Jacob K. Rosenstein Nanoscale working electrodes and miniaturized electroanalytical devices are valuable platforms to probe molecular phenomena and perform chemical analyses. However, the inherent close distance of metallic electrodes integrated into a small volume of electrolyte can complicate classical electroanalytical techniques. In this study, we use a scanning nanopipette contact probe as a model miniaturized electrochemical cell to demonstrate measurable side efects of the reaction occurring at a quasi-reference electrode. We provide evidence for in situ generation of nanoparticles in the absence of any electroactive species and we critically analyze the origin, nucleation, dissolution and dynamic behavior of these nanoparticles as they appear at the working electrode. It is crucial to recognize the implications of using quasi-reference electrodes in confned electrochemical cells, in order to accurately interpret the results of nanoscale electrochemical experiments. New insights into nanoscale chemical systems have come hand in hand with experimental techniques that can probe ever-smaller volumes, but traditional physiochemical models cannot necessarily be applied to systems with nanoscale dimensions. Tis fact, combined with the availability of new fabrication methods to prepare nano- scale electrodes and nanoconfned electrochemical devices, has inspired a new branch of study referred to as “nanoelectrochemistry”1–6. Physical size reductions yield important benefts such as reduced background noise, reduced iR drop, and fast mass transport rates, and these features can be used to study phenomena at length scales approaching the dimensions of single molecules7–15.
    [Show full text]
  • Platinum As a Reference Electrode in Electrochemical Measurements
    DOI: 10.1595/147106708X297855 Platinum as a Reference Electrode in Electrochemical Measurements By Kasem K. Kasem* and Stephanie Jones Department of Natural, Information, and Mathematical Science, Indiana University Kokomo, Kokomo, IN, 46904-9003, U.S.A.; *E-mail: [email protected] The usefulness of platinum as an electrochemical reference electrode was investigated. Well known redox systems with one-electron single or multiple redox waves, and two-electron multiple redox waves were used as test regimes. The effects on electrode performance of variables such as the solvent, the physical state of the electrolyte and its temperature were investigated. Cyclic voltammetry (CV) was used to derive kinetic parameters for comparison with corresponding measurements on traditional reference electrodes. The results indicate that Pt can be used as a reference electrode under specific conditions in which traditional reference electrodes cannot be used. Traditional reference electrodes used for elec- In certain electrolytes, modification of the Pt trochemical measurements, such as the calomel surface is important for its stability. Anodised, non- and silver/silver chloride electrodes, have a limited porous Pt has demonstrated its usefulness as a range of applicability. The liquid junction is prob- solid-state reference electrode by virtue of its near- lematic with these electrodes, and they cannot be Nernstian behaviour, low hysteresis and rapid used either with wholly solid-state electrochemical response (15). Modifications to Pt wire may extend cells or for very high-temperature reactions such as its usefulness to more electrochemical systems. The those in molten electrolytes. The use of solid plat- use of polypyrrole (16), poly-1,3-phenylendiamine inum electrodes in molten salts has been reported (15) or polyvinyl ferrocene (17) as a surface modifi- (1–14), but there are problems associated with the er can successfully suppress significant interference use in molten media of Pt electrodes.
    [Show full text]
  • Ch.14-16 Electrochemistry Redox Reaction
    Redox Reaction - the basics ox + red <=> red + ox Ch.14-16 1 2 1 2 Oxidizing Reducing Electrochemistry Agent Agent Redox reactions: involve transfer of electrons from one species to another. Oxidizing agent (oxidant): takes electrons Reducing agent (reductant): gives electrons Redox Reaction - the basics Balance Redox Reactions (Half Reactions) Reduced Oxidized 1. Write down the (two half) reactions. ox1 + red2 <=> red1 + ox2 2. Balance the (half) reactions (Mass and Charge): a. Start with elements other than H and O. Oxidizing Reducing Agent Agent b. Balance O by adding water. c. balance H by adding H+. Redox reactions: involve transfer of electrons from one d. Balancing charge by adding electrons. species to another. (3. Multiply each half reaction to make the number of Oxidizing agent (oxidant): takes electrons electrons equal. Reducing agent (reductant): gives electrons 4. Add the reactions and simplify.) Fe3+ + V2+ → Fe2+ + V3 + Example: Balance the two half reactions and redox Important Redox Titrants and the Reactions reaction equation of the titration of an acidic solution of Na2C2O4 (sodium oxalate, colorless) with KMnO4 (deep purple). Oxidizing Reagents (Oxidants) - 2- 2+ MnO4 (qa ) + C2O4 (qa ) → Mn (qa ) + CO2(g) (1)Potassium Permanganate +qa -qa 2-qa 16H ( ) + 2MnO4 ( ) + 5C2O4 ( ) → − + − 2+ 2+ MnO 4 +8H +5 e → Mn + 4 H2 O 2Mn (qa ) + 8H2O(l) + 10CO2( g) MnO − +4H+ + 3 e − → MnO( s )+ 2 H O Example: Balance 4 2 2 Sn2+ + Fe3+ <=> Sn4+ + Fe2+ − − 2− MnO4 + e→ MnO4 2+ - 3+ 2+ Fe + MnO4 <=> Fe + Mn 1 Important Redox Titrants
    [Show full text]