Titrations

10 Key excerpts on "Titrations"

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  eBook - PDF

  Analytical Chemistry

  A Toolkit for Scientists and Laboratory Technicians

  • Bryan M. Ham, Aihui MaHam(Authors)
  • 2024(Publication Date)
  • Wiley

    (Publisher)

  Titrimetric analysis is the process of measuring a substance of unknown concentration in a solution of interest via reaction with a standard that we have made that contains a known substance concentration. If we take a known weight or volume of our solid or solution of interest, we can calculate the concentration of the unknown from the measured use of our known concentration so- lution. Chemists call the standard solution the titrant solution. Analytical Chemistry: A Toolkit for Scientists and Laboratory Technicians, Second Edition. Bryan M. Ham and Aihui MaHam. © 2024 John Wiley & Sons, Inc. Published 2024 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/AnalyticalChemistry2e 10.2 REACTING RATIOS In a titration analysis, the reaction taking place is known with a predetermined stoichiometry. The analyst knows what com- pound is reacting with what compound and the moles of each. Suppose we have a compound “A” that is the titrant and a com- pound “B” that is our known substance of interest that we want to determine the concentration of. A simplified representation of the reaction is aA + bB → products (10.1) DERIVING THE TITRATION EQUATION 179 In the above reaction, a and b are the moles of reactants and are necessary to know to calculate concentrations. For example, the reaction of a titrant of dissolved silver (Ag + ) and chloride (Cl − ) in our test solution to produce the insoluble compound sil- ver chloride (AgCl) is represented as: Ag + (aq) + Cl − (aq) → AgCl(s) (10.2) where a = 1, b = 1, aq = aqueous (meaning the substance is in solution), and s = solid (meaning the substance is not in solu- tion). For the determination of sodium hydroxide with the titrant sulfuric acid, the reaction is: H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 O (10.3) In this case, a = 1 and b = 2. 10.3 THE EQUIVALENCE POINT When we are performing Titrations, it is most optimal if the reac- tion basically goes to completion in a very short amount of time.

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  Encyclopedia of Pharmaceutical Technology

  Volume 6

  • James Swarbrick(Author)
  • 2013(Publication Date)
  • CRC Press

    (Publisher)

  Technology– Tooling Titrimetry Vesa Virtanen Department of Pharmaceutical Product Development, Orion Pharma, Kuopio, Finland DEFINITION OF TERMS Titrimetry or titrimetric analysis is any method of quantitative chemical analysis in which the amount of a substance is determined by measuring the volume that it occupies or the volume of a second substance that is needed to react completely with the substance being determined. Titration is a process of chemical analysis in which the quantity of some constituents of a sample is determined by adding to the measured sample an exactly known quantity of another sub-stance with which the desired constituent reacts in a definite, known proportion. The reagent of exactly known composition used in a titration is called a stan-dard solution. The goal of titration is the equivalence point, where the addition of standard solution in an amount that is chemically equivalent to the substance with which it reacts. In fact, its position can be estimated only by observing physical changes associated with it in the solution. These changes manifest themselves at the endpoint of the titration. An indicator is a supplementary chemical compound that exhibits a change in color as a result of concentration changes occurring near the equivalence point. PRECIPITATION Titrations In these Titrations, the determination of the substance is effected by precipitating it in the form of an ‘‘insolu-ble’’ compound of known composition. The equiva-lence point is reached when sufficient reagent to complete precipitation has been added. In practice, the insoluble reaction product formed will be very slightly soluble and to an extent that depends on the amount of solvent present as well as on the nature and amounts of other ions and compounds present.

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  eBook - ePub

  Introduction to Pharmaceutical Analytical Chemistry

  • Stig Pedersen-Bjergaard, Bente Gammelgaard, Trine G. Halvorsen(Authors)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  5 Titration

  1. 5.1 Introduction
  2. 5.2 Potentiometric Titration and Electrodes
  3. 5.3 Aqueous Acid–Base Titrations
  4. 5.4 Titration in Non‐aqueous Solvents
  5. 5.5 Redox Titrations
  6. 5.6 Alternative Principles of Titration

  5.1 Introduction

  Titration is a quantitative technique and methods based on titration provide high accuracy (99.5–100.5%) and precision (<0.5% relative standard deviation (RSD )). Titration is an official method in the European Pharmacopoeia (Ph. Eur. ) and in the United States Pharmacopoeia (USP ). In pharmaceutical analysis, titration is mainly used for quantitative analysis (assay) of active pharmaceutical ingredient s (API s) and excipients with the purpose of assessing the purity of a given substance (analyte).

  Titrations are based on measurement of volumes. An accurate amount of analyte is dissolved in a specific volume of solution. This solution is termed the titrate. Increments of a standardized solution of a reagent are added gradually until the entire amount of analyte has reacted. The standardized solution is termed the titrant. The concentration and exact volume of titrant added are used to calculate the amount of analyte. More generally, a titration can be described by the following titration equation:

  (5.1)

  Here x and y are the number of mol of analyte (pharmaceutical compound) and titrant involved to complete the titration. The titration is completed when all the analyte has reacted and transformed to products. The titration has then reached the equivalence point.

  The titrant is added either manually from a burette (see Figure 5.1 ) or automatically from an automatic titration apparatus termed an automatic burette or titrator.

  Figure 5.1

  Schematic view of the burette used for titration

  Detection of the equivalence point can be based on visual inspection of colour change (Indicator detection) or based on electrochemical measurements (Potentiometric endpoint detection). In the latter case, the titration is often termed Potentiometric titration

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  eBook - ePub

  Understanding Experimental Planning for Advanced Level Chemistry

  The Learner's Approach

  • Kim Seng Chan, Jeanne Tan(Authors)
  • 2015(Publication Date)
  • WSPC

    (Publisher)

  CHAPTER 1 PLANNING USING TITRATION

  Titration refers to a general class of experiments in which the known property (e.g., concentration) of a solution is used to infer the unknown property of another solution. A typical titration experiment requires the following apparatus:

  —Pipette and pipette filler to measure the volume of the analyte or titrand; —Burette to contain the standard solution or titrant; —Conical flask to contain the analyte or titrand; —Volumetric flask to make a standard solution or for carrying out a dilution; and —An indicator (optional) such as phenolphthalein, methyl orange, starch, etc. to signal the end of a titration. A titration set-up is shown as follows:

  Q	What is a standard solution?

  A: A standard solution refers to one in which its concentration is already known accurately. Since the concentration of the solution is already known, when we used a certain volume of this standard solution, we would know the number of moles of particles that is used. Hence, we can make use of this information about the number of moles to determine the number of moles of reactants in the analyte, through a balanced chemical equation.

  Q	Why is a burette used to hold the standard solution?

  A: A burette can measure up to two decimal places of accuracy while a pipette can only measure up to one decimal place of accuracy. Since a burette is more accurate than a pipette, it is usually used to contain the standard solution. But take note that there are exceptions in which a burette can be used to contain the non-standard solution that is used during titration. For such instances, there are usually other specific reasons for doing it.

  1.1Mixture of Potassium Hydrogen Carbonate and Potassium Chloride

  The Task:

  A sample of potassium hydrogen carbonate, KHCO3

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  eBook - PDF

  Basic Analytical Chemistry

  • L. Pataki, E. Zapp, R. Belcher, D Betteridge, L Meites(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  3.2 Titrimetric analysis Titrimetric analysis consists essentially of adding a standard solution (that is, of known concentration) or titrant to the test solution, and determining the amount of a component of the sample from the added 202 BASIC ANALYTICAL CHEMISTRY volume (the titre) of the titrant. The titrant is added to the solution of the sample until the equivalence point is reached. This procedure is called titration. The main criteria for feasibility of titrimetric analysis are as follows: (i) The chemical reaction between the component to be determined and the titrant must be a complete, stoichiometrically unambiguous reaction, which can be represented by a simple chemical equation; (ii) The reaction must be fast; (iii) There must be an abrupt change in at least one of the physico-chemical properties of the solution at the equivalence point; (iv) The equivalence point must be detectable, for example by a change in colour of certain compounds (indicators) or in the electrical properties of the solution. The main advantage of titrimetry over gravimetry is its speed. As the measurement of volume is less accurate than weighing, titrimetric methods are usually less accurate than gravimetric ones. The added amount of standard solution can, of course, also be weighed, using a weight burette, but in this case the greatest advantage, the speed of determination, is lost. According to Chariot, a reaction in solution can be regarded essen-tially as an exchange. The various types of reactions can therefore be characterized by the equations donor I ;± p + acceptor I p + acceptor II ;± donor II donor I -f acceptor II ;± donor II -f acceptor I where p is the species transferred in the reaction. In order to find an appropriate method by which the equivalence point of a titration can be indicated, it is indispensible to investigate the equilibrium conditions of the species formed or consumed in the reaction at certain points in the titration.

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  eBook - ePub

  Introduction to Pharmaceutical Chemical Analysis

  • Steen Honoré Hansen, Stig Pedersen-Bjergaard, Knut Rasmussen(Authors)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  Chapter 5 Titrimetric Methods

  This chapter discusses the principles of quantitative analysis based on titrimetric methods. Titrimetric methods are official methods in the European Pharmacopeia and are used for quality control of active pharmaceutical ingredients (APIs) and excipients. The chapter focuses on Titrations based on acid–base reactions and redox reactions and also gives an overview of various principles of endpoint detection. Examples of titrimetric methods for the quantitative determination of APIs and excipients are discussed in Chapter 21.

  5.1 Introduction

  In titrimetric methods the volume of a reagent needed to react with an analyte is normally measured. To the analyte solution are added increments of a reagent solution (titrant ) of a precisely known concentration until the reaction between the reagent and the analyte is complete. The titrant is added either manually from a burette (see Figure 5.1 ) or from an automatic titration apparatus , so that the volume of titrant is controlled at all times during the titration .

  Figure 5.1 Burette used for titration

  A titrimetric reaction can be illustrated by the following equation:

  (5.1)

  where x and y is the number of moles of analyte and titrant needed to complete the titration. Titration is finished when virtually all the analyte has reacted and is transferred to products. The titration has reached the equivalence point . The amount of reagent consumed is read on the burette, and the quantity of analyte in the sample solution can be calculated on the basis of knowledge of the values of x and y . An example of such a calculation is shown in Box 5.1.

  Box 5.1 Calculation of the concentration of analyte in a titrimetric method

  A sample solution of H2 SO4 of unknown concentration was titrated with a solution of 1.056 M NaOH to determine the molar concentration of H2 SO4 . 25.00 ml of the sample solution was titrated to the equivalence point with 23.55 ml of NaOH solution. H2 SO4

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  eBook - PDF

  Introductory Titrimetric and Gravimetric Analysis

  The Commonwealth and International Library: Chemistry Division

  • Evelyn M. Rattenbury(Author)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  P A R T I Titrimetric Analysis This page intentionally left blank C H A P T E R 1 Introduction and General Principles IN TITRIMETRIC analysisf the concentration of a solution is determined by causing the solution to react with another solution of known concentration. A definite volume, usually 25 ml, is taken of one of the solutions and the other solution is added carefully, until reaction is complete and neither substance is present in excess. The volume of the second solution is noted, thus enabling the concentration of the first solution to be calculated. The unit of volume is the litre (1.) and is the volume occupied by one kilogram of pure water at its temperature of maximum density and under normal atmospheric pressure. One millilitre (ml) is a thousandth part of a litre. The millilitre is almost equal to the cubic centimetre (cm 3 ):% 1 ml = 1-000028 cm 3 . (1927) The chemical reaction must be known so that an equation can be written to represent the chemical change. For example, the reaction between hydrochloric acid solution (HCl) and sodium carbonate solution (Na 2 CC >3) may be represented : N a 2 C 0 3 + 2HC1 = 2NaCl + H 2 0 + C 0 2 or, as ions : 2Na+ + CO-+ 2H + 4- 2C1 - = 2Na+ + 2C1 - + H 2 0 + C 0 2 t The term volumetric analysis'* is often used; this term includes the measurement of gaseous volumes. % It has recently been recommended, by e.g. the International Standards Organization, that the terms litre and millilitre should be used to represent the exact cubic decimetre and cubic centimetre respectively. 3 4 TITRIMETRIC A N D G R A V I M E T R I C A N A L Y S I S The equation must be inspected so that the equivalent weight(s) of the particular substance(s) may be deduced. In the example above, a mole (the molecular weight expressed in grams) of sodium carbonate reacts with exactly 2 moles of hydrochloric acid.

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  Aquatic Chemistry Concepts, Second Edition

  • James F. Pankow(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  For alkalimetric and acidimetric Titrations, the titration curve is usually plotted as pH vs. amount (e.g., volume) of strong base or strong acid added. Here, however, since we want to discuss things in a general context, for the x -axis rather than volume, we will mostly use the value of C B − C A that is produced in the solution (or the related parameter f, defined below). If the concentration in the titrant is sufficiently large relative to the concentration of what is being titrated (say 20×), then near-constancy in the value of A T (or B T, etc.) in the solution can be assumed over the course of the titration: the volume of titrant added does not significantly increase the volume of solution being titrated so that A T (or B T, etc.) is not significantly lowered during the titration. This assumption simplifies computing titration curves. While the mathematics of Titrations might be viewed as, well, tedious and confusing, it is fundamentally important for understanding how aqueous solutions behave in response to changes in acid or base content. First, most of the salt in the oceans is the result of the grand back-and-forth chemical neutralization that has occurred over geologic time of metal oxide bases from terrestrial solids reacting with added HCl from volcanism and vice versa (Schilling et al., 1978). Second, natural waters undergo titration changes whenever there are spills of strong acid or base, and when acid rain falls on a lake watershed system. Third, laboratory Titrations are routinely used in analytical determinations of “alkalinity” in samples of: (1) natural water; and (2) water flowing through waste and drinking water treatment plants, to provide input information for calculations regarding pH control

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  Fundamentals of Analytical Chemistry

  • Douglas Skoog, Donald West, F. Holler, Stanley Crouch, Douglas Skoog(Authors)
  • 2021(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  This greater sensitivity makes it possible to choose sample sizes that lead to significantly smaller consumption of standard reagents. 4. Gravimetric Titrations are more easily automated than are volumetric Titrations. 11E Titration Curves As noted in Section 11A-1, an end point is signaled by an observable physical change near the equivalence point of a titration. The two most widely used signals involve (1) changes in color due to the reagent (titrant), the analyte, or an indicator and (2) a change in potential of an electrode that responds to the titrant concentration or the analyte concentration. To understand the theoretical basis of end-point determinations and the sources of titration errors, calculate the data points necessary to construct titration curves for the systems under consideration. A titration curve is a plot of some function of the analyte or titrant concentration on the y-axis versus titrant volume on the x-axis. The weight concentration in mol of solute/kg solution is similar to the solution molality, which is mol of solute/kg solvent. In dilute solution, these are identical, but in more concentrated solution, 1 kg of solution may not equal 1 kg of solvent. ❯ Titration curves are plots of a concentration-related variable versus titrant volume. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 11E Titration Curves 281 11E-1 Types of Titration Curves Two general types of titration curves (and thus two general types of end points) occur in titrimetric methods.

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  Analytical Chemistry

  • Clyde Frank(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Chapter Fourteen

  Precipitation Titrations

  Publisher Summary

  This chapter explains the definition of precipitation titration, in which a substance is titrated with a standard solution of a precipitating agent. At the completion of the precipitation, which is defined by stoichiometry of the reaction, either the appearance of excess titrant or the disappearance of the reactant is detected. Detection of the stoichiometric point is accomplished by color indicators as well as by instrumental methods. Of the latter, the principal technique is potentiometric measurement, which involves the usage of indicator or ion-selective type electrodes. The main difference between a precipitation titration and other volumetric methods is that a precipitate forms during the course of the titration. The titration requirements include the formation of a stoichiometric precipitate as well as those typical to most volumetric procedures. A stoichiometric relationship between the titrant and sample leading to precipitation is possible. Even though the precipitate is not isolated, the adsorptive nature of the precipitate toward the titrant leads to large errors.

  INTRODUCTION

  A precipitation titration is one in which a substance is titrated with a standard solution of a precipitating agent. At the completion of the precipitation, which is defined by the stoichiometry of the reaction, either the appearance of excess titrant or the disappearance of the reactant is detected. Detection of the stoichiometric point can be accomplished by color indicators as well as by instrumental methods. Of the latter, the principal technique is potentiometric measurement using indicator or ion-selective type electrodes.

  The idea of a precipitation titration is a very old one. For example, Gay-Lussac in 1832 determined silver ion with chloride. Mohr and Volhard, whose names identify specific precipitation procedures involving silver ion and halides, made their contributions in 1856 and 1874, respectively. In the early 1900s the formation of turbidity (AgCl) in a titration procedure was successfully used to determine the atomic weight of silver, chlorine, and several metals isolated as pure metal chlorides.

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