Chemistry
Redox Titration
Redox titration is a type of titration that involves the transfer of electrons between the reactants. It is used to determine the concentration of an unknown solution by comparing it to a standard solution of known concentration. The endpoint of the titration is reached when the reaction between the two solutions is complete.
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9 Key excerpts on "Redox Titration"
- Anju Goyal, Harish Kumar, Anju Goyal, Harish Kumar(Authors)
- 2022(Publication Date)
- Bentham Science Publishers(Publisher)
Redox TitrationsSapna Kumari,1 , *Anju Goyal1,Madhukar Garg11 Chitkara College of Pharmacy, Chitkara University, Rajpura, Punjab, IndiaAbstract
Redox Titrations are the titrimetric method developed to know the concentration of the analyte by creating redox reaction among titrant and analyte. The basic principle involved in the Redox Titration is the oxidation-reduction reaction, in which electron transfer from one reactant to another reactant takes place. Oxidation means loss of electron and reduction means gain of electron. These must happen at the same time, when a substance loses electrons, there must be some other substance to accept those electrons. The main applications associated with Redox Titrations are determining the reduction potential of sHdrA flavin from Hyphomicrobium denitrificans, water in non-aqueous solutions, dissolved oxygen in water and determination of alcohol content in the whiskey bottles, etc.Keywords: Oxidation, Redox Titrations, Reduction, Titrimetric methods.* Corresponding author Sapna Kumari: Chitkara College of Pharmacy, Chitkara University, Rajpura, Punjab, India; E-mail: [email protected]INTRODUCTION
Redox Titrations are the titrimetric method based upon the electron transfer between the reactants or change in the oxidation number of the reactant. Popularly, these are well known as oxidation-reduction titrations, as these involve the titration of the reducing agent with a standard solution of an oxidizing agent and vice versa. Most commonly, this method is used in the laboratory for determining the concentration of a given analyte via triggering a redox reaction between the analyte and the titrant. Sometimes, these types of titrations needed a potentiometer or a redox indicator to identify unknown analytes [1 ].History And Development Of Redox Titration Method
Redox Titrations were announced just after the progression of acid–base titrimetry. The initial methods acquired the benefit of the oxidizing power of chlorine. In 1787, Claude Berthollet introduced a new method for the analysis of chlorine water (a mixture of Cl2
eBook - ePub- Clyde Frank(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Chapter ElevenOxidation–Reduction Titrations
Publisher Summary
A redox reaction is used for a titration and meets the general requirements that apply to other successful titration procedures. Many different inorganic species exist in more than one stable oxidation state and can frequently be determined through a Redox Titration. Certain organic functional groups are quantitatively oxidized or reduced and are analyzed by a titration procedure. This chapter discusses the feasibility of Redox Titrations and end-point detections by color indicators and potentiometry. Redox reactions tend to be slow, and often the redox reaction becomes useful after a suitable catalyst becomes available. The chapter also explains the Redox Titration curve, which describes the change in concentration of the species of interest as a function of the titrant. It is possible to predict the shape of a titration curve prior to carrying out the titration in the laboratory.INTRODUCTION
If a redox reaction is to be used for a titration, it must meet the same general requirements that apply to other successful titration procedures. Consequently, the reaction should be rapid, go to completion, be stoichiometric, and a means for end-point detection should be available. Many different inorganic species exist in more than one stable oxidation state and frequently can be determined through a Redox Titration. Similarly, certain organic functional groups are quantitatively oxidized or reduced and can, therefore, be analyzed by a titration procedure. In this chapter the feasibility of Redox Titrations and end-point detection by color indicators and potentiometry are considered.In general, redox reactions tend to be slow and often the redox reaction only becomes useful after a suitable catalyst becomes available. For example, the best way to standardize Ce4+ solutions is by titrating primary standard As2 O3 [tris-1,10-phenthroline iron (II) is used as indicator]. However, poor results are obtained because the reaction rate is too slow. If OsO4 is added as a catalyst, the reaction proceeds conveniently and an accurate standardization is obtained. It is difficult to generalize in regard to useful catalysts for redox reactions. Some are catalyzed by acid, others by base, and still others by metal ions. Also, there are reactions, such as Fe2+ –Ce4+ , I2 –S2 O3 2− , BrO− –Br−
- Stig Pedersen-Bjergaard, Bente Gammelgaard, Trine G. Halvorsen(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
Redox Titrations. A Redox Titration can be described by the following equation:(5.18)The subscript 1 refers to the titrate and 2 refers to the titrant, respectively. The reduction potential of a given substance is an expression of the extent to which the substance may take up electrons. A high positive value for the reduction potential indicates:- The substance is easily reduced.
- The substance is a powerful oxidizing agent.
- The substance easily removes electrons from other substances with a lower reduction potential.
Table 5.3 list values for standard reduction potentials (E0 ) for typical redox pairs.Table 5.3Standard reduction potentials (E0 )Oxidized form Reduced form E0 (V)Ce4+ + e−Ce3+1.61 MnO4 − + 5e− + 8H+ Mn2+ + 4H2 O1.51 Fe3+ + e−Fe2+0.55 Br2 + 2e−2Br−1.05 I2 + 2e−2I−0.54 2H+ + 2e−H20.00 Fe2+ + 2e−Fe −0.44 Ca2+ + 2e−Ca −2.89 A substance with a higher reduction potential oxidizes a compound with a lower reduction potential. For titrations in general, the equilibrium constant should be high to ensure a complete reaction. In Redox Titration, the equilibrium constant is determined by the difference (ΔE) between the reduction potentials of the two substances:(5.19)E0 T is the reduction potential of the titrant and E0 A is the reduction potential of the analyte (titrate). ΔE is termed the reaction potential. In practice, ΔE should not be less than 0.1–0.2 V. Throughout titration, the potential changes gradually with addition of the titrant, and at the equivalence point the potential increases or decreases very sharply as a function of the added titrant. An example of this is shown in Figure 5.11 for the titration of iron (II) (Fe2+ ) with cerium (IV) (Ce4+
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
See Section 14.8 below for typical procedures. Some examples of useful Redox Titrations include measuring the ascorbic acid (a reducing agent) content of vitamin C tablets, or of sulfur dioxide in wines, by titration with iodine. The Karl Fisher titration of water in samples involves iodine. The measure of saturation in a fatty acid is determined as the iodine or bromine number, in which the grams of iodine or bromine absorbed by a 100-gram sample are measured. The iron content of an ore can be determined by titration of iron(II) with potassium permanganate. 14.1 First: Balance the Reduction – Oxidation Reaction The calculations in volumetric analysis require a balanced reaction. The balancing of redox reactions is reviewed on the text website. 437 438 CHAPTER 14 REDOX AND POTENTIOMETRIC TITRATIONS Various methods are used to balance redox reactions, and we shall use the half-reaction method. In this technique, the reaction is broken down into two parts: There are various ways of balancing redox reactions. Use the method you are most comfortable with. A more thorough review is available on the text website. the oxidizing part and the reducing part. In every redox reaction, an oxidizing agent reacts with a reducing agent. The oxidizing agent is reduced in the reaction while the reducing agent is oxidized. Each of these constitutes a half-reaction, and the overall reaction can be broken down into these two half-reactions. Thus, in the reaction Fe 2+ + Ce 4+ → Fe 3+ + Ce 3+ Fe 2+ is the reducing agent and Ce 4+ is the oxidizing agent. The corresponding half-reactions are: Fe 2+ → Fe 3+ + e − and Ce 4+ + e − → Ce 3+ To balance a reduction – oxidation reaction, each half-reaction is first balanced. There must be a net gain or loss of zero electrons in the overall reaction, and so the second step is multiplication of one or both of the half-reactions by an appropriate factor or factors so that, when they are added, the electrons cancel.
eBook - PDF- L. Pataki, E. Zapp, R. Belcher, D Betteridge, L Meites(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
The red iron(III) thiocyanate complex is decolourized by reducing titrants. Applications of redox reactions The application of oxidants to determine organic and inorganic reductants is the most widespread use of redox titrimetry. The use of reducing titrants is considerably less important because sufficiently strong reductants are very sensitive to atmospheric oxygen in aqueous solutions. To select an appropriate system, it is important to consider the difference in standard electrode potential, the effects of other components of the solution such as hydrogen ions and complexing agents, and possible inhibition or induction effects. 280 BASIC ANALYTICAL CHEMISTRY Before determining an oxidant or a reductant, a suitable standard solution is first chosen on the above basis, and the appropriate condi-tions provided. If the species to be determined is present in oxidized and reduced forms, the species must be quantitatively converted before titration into the oxidation state suitable for titration by the chosen titrant, that is, prior oxidation or reduction must be carried out. The oxidants or reductants used in these operations must give rise to a quantitative reaction under the given conditions, and the excess of the oxidant or reductant must not interfere with the deter-mination. These requirements can be met by reagents that exert the desired action only under certain conditions. Concentrated (70%) perchloric acid, for instance, is a particularly strong oxidant at its boiling point, but after dilution it does not interfere in Redox Titrations. Qui nones may be reduced by ethanol in concentrated hydrochloric acid medium, but on diluting the solution, the ethanol may not react with the oxi-dizing titrant. Reduction may be accomplished with easily removable substances such as metals and their amalgams. The use of poorly soluble sodium bismuthate for oxidation purposes is also based on its ease of removal after use.
eBook - ePub- Steen Honoré Hansen, Stig Pedersen-Bjergaard, Knut Rasmussen(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
Point 1 highlights that, in titrimetric reactions, we need to know the exact amount of titrant that reacts with each mole of analyte. This requirement is necessary to calculate the amount of analyte in the sample, as exemplified in Box 5.1. This requirement also means that the analyte and the reagent must react in a well defined manner without the possibility of side reactions. Criteria 2 and 3 are also very fundamental. If the reaction does not progress to almost 100% or if other drug substances also consume the titrant, the consumption of reagent cannot be correlated to the amount of analyte in the sample solution. Criterion 4 is not essential, but it is an advantage that the reaction between the analyte and the reagent is fast, so that the titration can be performed in a short time. Criterion 5 states that we must have a method to detect when the equivalence point is reached, so that we can end the titration and read the consumption of titrant for calculation of the concentration of analyte. As shown in Box 5.1, these calculations assume that the concentration of titrant is known (Criterion 6).Reactions used in titrimetric methods may be of several types, and in this chapter, the following types are described:- Acid–base reactions (acid–base titration );
- Reduction–oxidation reactions (Redox Titration );
- Complexometric reactions (complexometric titration ).
The emphasis will be placed on acid–base and Redox Titrations, while complexometric titrations will only be discussed briefly. In addition to characterizing the titration according to the chemical principle as the basis for the reaction, it is customary to characterize the titration by the method used to detect the equivalence point of titration. Of the most important detection methods are visual detection (color change) and detection using potentiometry .During the titration the titrant is added to the solution until the equivalent point is reached, where virtually all the analyte has been converted into products. We do not write that 100% of the analyte has been converted into products due the fact that all titrimetric reactions are equilibrium reactions which means that Equation (5.1)
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
© 1993 Richard Megna/Fundamental Photographs coated with a very thin film of aluminum oxide, Al 2 O 3 , so thin that it doesn’t obscure the shin- iness of the metal beneath. This oxide coating adheres very tightly to the surface of the metal and makes it very difficult for additional oxygen to combine with the aluminum. Therefore, further oxidation of aluminum occurs very slowly. On the other hand, powdered aluminum, which has a large surface area, reacts violently when ignited and is part of the propellant in the booster rockets for the space shuttle. 5.6 Stoichiometry of Redox Reactions In general, working stoichiometry problems involving redox reactions follows the same prin- ciples we’ve applied to other reactions. The principal difference is that the chemical equations are more complex. Nevertheless, once we have a balanced equation, the moles of substances involved in the reaction are related by the coefficients in the balanced equation. Because so many reactions involve oxidation and reduction, it should not be surprising that they have useful applications in the lab. Some redox reactions are especially useful in chemical analyses, particularly in titrations. In acid–base titrations, we often need a specific indicator for each reaction to signal the end point. However, there are not many indicators that can be used to conveniently signal the end points in Redox Titrations. In practice, there are a few oxidizing agents that are highly colored and can act as their own indicator, so we rely on color changes of the reactants themselves. One of the most useful reactants for Redox Titrations is potassium perman- ganate, KMnO 4 , especially when the reaction can be carried out in an acidic solution. Permanganate ion is a powerful oxidizing agent, so it oxidizes most substances that are capable of being oxidized.
eBook - ePub- John Kenkel(Author)
- 2013(Publication Date)
- CRC Press(Publisher)
4 are added prior to beginning the titration. The permanganate concentration is 0.1 N.(Reference: The Official Compendia of Standards , U.S. Pharmacopeia and National Formulary (2000), The location is Rockville, MD, USA, p. 836.)An important application of iodometry can be found in many wastewater treatment plant laboratories. Chlorine, Cl2 , is used in a final treatment process prior to allowing the wastewater effluent to flow into a nearby river. Of course, the chlorine in both the free and combined forms can be just as harmful environmentally as many components in the raw wastewater. Thus, an important measurement for the laboratory to make is the amount of residual chlorine remaining unreacted in the effluent. Such chlorine, which is an oxidizing agent, can be determined by iodometry. It is the “O” in Figure 5.22 .FIGURE 5.22 In iodometry, a solution of KI is added to a solution of the analyte, represented here by “O.” The products are “R” and iodine, I2 . The iodine formed is then titrated with standardized sodium thiosulfate. It is an indirect titration, since the I2 is titrated, but the analyte is “O.” Refer back to Figure 5.14 for an illustration of an indirect acid–base titration.5.7.4.3 Prereduction and Preoxidation
Perhaps the most important application of redox chemicals in the modern laboratory is in oxidation or reduction reactions that are required as part of a preparation scheme. Such “preoxidation” or “prereduction” is also frequently required for certain instrumental procedures for which a specific oxidation state is required to measure whatever property is measured by the instrument. An example in this textbook can be found in Experiment (the hydroxylamine hydrochloride keeps the iron in the +2 state). Also in wastewater treatment plants, it is important to measure dissolved oxygen (“DO”). In this procedure, Mn(OH)2 reacts with the oxygen in basic solution to form Mn(OH)3
eBook - ePubChemistry
With Inorganic Qualitative Analysis
- Therald Moeller(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
19OXIDATION AND REDUCTION
Publisher Summary
This chapter explores the meaning of the terms “oxidation” and “reduction”. It presents the concept of electrochemistry to make clear the relationships among redox reactions and what happens in electrochemical cells. The chapter describes the balancing of redox equations. It presents the understanding and using of standard reduction potentials. The chapter discusses Nernst equation and explains the determination of equilibrium constants from standard reduction potentials. An oxidation-reduction reaction can be thought of as the sum of two half reactions. Each ion-electron equation includes both the oxidized form and the reduced form of the same species. Therefore, a complete redox equation contains at least two oxidants, the electron acceptors and two reductants, the electron donors.In this chapter the meaning of the terms “oxidation” and “reduction” is explored, and just enough electrochemistry is presented to make clear the relationships between redox reactions and what happens in electrochemical cells. (The electrochemical cells themselves are discussed in Chapter 24 .) The main additional topics covered are balancing redox equations, understanding and using standard reduction potentials, and the Nernst equation and the determination of equilibrium constants from standard reduction potentials.T“Oxidation” and “reduction” are other words that have undergone changes in meaning. Earlierhe English language, like most others, is constantly changing. Words go out of fashion and disappear, new words are coined as new ideas and materials develop, and, most importantly, well-established words gradually assume new meanings. Consider, for example, the word “tremendous.” It was adapted into our language from a Latin word which meant “to cause to tremble”; that is, “awesome,” “dreadful,” “fearful.” Because we imagine awful and dreadful things to be very large, the word has come to mean “large.”
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