The potential is directly proportional to the concentration of the ions. Arrows show the direction of net transfer for each ion, and their lengths indicate. Reference electrode indicator electrode reference electrode. Solidstate electrodes these are made of inorganic salt crystals. It is a measure of the reducibility of the species in solution. This arrangement is referred to as a combination electrode. For potentiometric sensors, an accurate and stable reference electrode that. Reference electrode standard hydrogen electrode agagcl reference electrode. Ion selective electrodes, potentiometry, and potentiometric titrations. These types of reference electrodes are used almost exclusively in nonaqueous systems see chaps.
A reference electrode is an electrode which has a stable and wellknown electrode potential. A reference is an electrode that has the halfcell potential known, constant, and completely insensitive to the composition of the solution under study. However, the rapid development of new selective electrodes and. Many different types of indicator electrodes can be used as endpoint indicators in potentiometric titrations. This glass is mostly amorphous silicon dioxide sio 2. Electroanalysis with membrane electrodes and liquid liquid. Potentiometry potentiometry is the use of electrodes to measure voltages that provide chemical information. Contact to the measurement cell is made through a porous glass frit or fiber which allows the movement of ions, but not the bulk solution. Pdf solidstate reference electrodes for potentiometric. Reversible metalmetal ion with salt of the metal ion and excess anion x, e. Glab, in encyclopedia of analytical science third edition, 20. In both electrodes, the activity of the metal ion is fixed by the solubility of the metal salt.
Reference electrode junction with studied solution, usually made from ceramics or capillary with asbestos or quartz fiber reference internal solution internal electrode ise internal solution sensing part of the electrode. For example, an acidbase titration can be performed with a glass electrode as endpoint detector instead of using colored indicators, or chloride ions can be titrated with silveri. Inert metals used in oxidationreduction electrolytic cells. Use of a high impedance voltmeter in important, because it ensures that current flow is negligible. The unknown solution is converted into a halfcell by adding an electrode e.
Reference electrode electrochemistry chemistry class. To do this, two electrodes are used, an indicator electrode the glass electrode and metal ion indicator electrode and a reference electrode. It is used for all types of volumetric analysis acid base, precipitimetry, complexometry and. Since the potential of the reference electrode is constant, it is the potential developed. The third component of a potentiometric cell is a salt bridge that prevents the components of the analyte solution from mixing with those reference electrode. Types of ionselective electrodes there is four classes of ionselective electrodes. View notes chem2041 electrochem lecture part 2 1 slides per page. This socalled reference electrode allows control of the. The potential or emf of a solution depends on the nature and concentration of the ions of the test substance. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
Most potentiometric methods employ one of two other common reference halfcells the saturated calomel electrode sce or the silversilver. Metallic indicator electrode and membrane electrodes are types of indicator electrodes. Electrodes and potentiometry metals ag, cu, zn, cd, hg can be used to monitor their aqueous ions. Alternative strategy for manufacturing of allsolidstate reference. Application the sce is used in ph measurement, cyclic voltammetry and general aqueous electrochemistry. Platinum or au are used as metal indicator electrodes. Do not place the electrodes anywhere except attached to the electrode holder. Species that are in an electrochemical cell can interfere with the performance of an.
An indicator electrode has a potential that varies with variations in the concentration of an analyte. Most indicator electrodes used in potentiometry are selective in their responses. The ph electrode and potentiometric titrations in this experiment you will investigate the nernstian response of a ph electrode, perform potentiometric titrations, investigate the acidbase properties of the bicarbonate buffer system. Potentiometric titration is a method of chemical analysis.
In conjunction with this reference is the indicator or working electrode, whose. In many electrodes designed for potentiometry, the reference half cell is contained within the body of the sensing electrode. Potentiometry chapter 23 potentiometry reference electrodes a reference is an electrode that has the halfcell potential known. Indicator electrode an overview sciencedirect topics. These topics include junction potentials, reference electrodes, and the nernst equation. In potentiometric measurements, the potential between two electrodes is measured using a high impedance voltmeter. To use this electrode system, it is necessary to introduce a small concentration of. Chapter 22 introduction to electroanalytical chemistry. Two kinds of reference electrodes were manufactured by mixing these. Chapter 22 introduction to electroanalytical chemistry electroanalytical methods are a class of techniques in analytical chemistry, which study an analyte by measuring the potential volts andor current amperes in an electrochemical cell containing the analyte. The reference electrode in most electrochemical measurements is composed of an electrode of the second kind, in most cases agagcl, in contact with a solution of defined chloride concentration, typically 3m kcl. Introduction to ionselective electrodes so far you have learned that during the technique of potentiometry, the potential, or voltage, of an electrochemical cell is measured. Electrodes and potentiometry relating concentration to electrode potential classification of electrode types electrodes as half cells for electroanalytical techniques involve redox reactions electrodes of zeroth, 1st, 2nd and 3rd kind. Several types of liquid membrane and solidstate reference.
Potentiometric titration is a technique similar to direct titration of a redox reaction. The two reference electrodes serve to measure the electric potential difference across the membrane. Common reference electrodes used in potentiometry i calomel electrodes hg in contact with hg 2 cl 2. In spite of various suggestions to solve the problem, no type of solidstate reference electrode is so far available with properties completely. This electrode and the silversilver chloride reference electrode work in the same way. They are composed of the metal rod immersed in its metal solution. Pdf solidstate reference electrodes for potentiometric sensors. Potentiometric titration with its principle, applications. The instrumentation used to perform potentiometry is straightforward, consisting of an indicator electrode, a reference electrode, and a potential measuring device. Reference electrodes a reference is an electrode that has the halfcell potential known, constant, and completely insensitive to the composition of the solution under study.
The inorganic salt is made such to have vacancies in its lattice structure. These are mainly used for the determination of the analyte by maintaining the fixed potential. Classification of electrode types electrodes and potentiometry relating concentration to electrode potential class 1. This simplicity makes potentiometry an inexpensive technique compared to atomic spectroscopy or ion chromatography. Potentiometry and types of electrodes flashcards quizlet. One of the electrodes is a reference electrode, whose electrode potential is known. Properties of umass boston l is call ionophone, which is a ligand. Potentiometric titrations electrodes used in potentiometric titrations the experimental setup for potentiometric measurement comprises a set of an indicating and reference electrodes or two identical indicating electrodes, which should be treated carefully.
Potentiometry reference electrodes most common types of reference electrodes. Potentiometry is a classical analytical technique with roots before the twentieth century. This forms an insoluble layer of agcl on the surface of the electrode and gives you an. In conjunction with this reference is the indicator or working electrode, whose response depends upon the analyte concentration. These are mainly classified into three types of electrodes used in the potentiometry. Electrodes and potetiometry minnesota state university.
How to select the proper one for measuring a given analyte. Reference electrode an overview sciencedirect topics. We explore here for the first time the direct potentiometric detectability of calcium, lead, and silver ions in amounts on the order of 300 attomoles at 100 picomolar concentrations without any preconcentration, analyte recycling, or electrocatalytic signal enhancement. The cell consists of both an indicator and reference electrode. The high stability of the electrode potential is usually reached by employing a redox system with constant buffered or saturated concentrations of each participant of the redox reaction.
Indicator electrodes indicator electrodes respond to a given half reaction yet dont participate in the redox reaction itself. Mainly two electrodes are used in the potentiometry. Pdf in most electrochemical measurements, it is necessary to keep one of the. This technqiue relies on the measurement of electromotive force emf of a solution using a set of indicator and reference electrodes. In potentiometry, those two electrodes are generally called the indicator electrode and the reference electrode. Start studying potentiometry and types of electrodes. The potential difference is determined by the electrochemical cell which is composed of pair of electrodes namely the indicator electrode and the reference electrode. Metallic indicator electrode four main types b metallic electrodes of the second kind. Electrodes and potentiometry the use of electrodes to measure voltages that provide chemical. For a long time, considerable efforts have been made to. Instead, selective migration of one type of ion across an electrode. Potentiometry is mainly used to determine the potential or the electromotive force of a sample solution. Electrodes and potentiometry analytical chemists design electrodes voltage sensitive to conc.
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