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INTRODUCTION TO IODOMETRIC AND IODIMETRIC TITRATIONS

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1 INTRODUCTION TO IODOMETRIC AND IODIMETRIC TITRATIONS
Fact File 1: INTRODUCTION TO IODOMETRIC AND IODIMETRIC TITRATIONS © Barreiro,L. & Navés, T 2007 English Revision: Bedford, N. Awarded from the Generalitat de Catalunya, 2006 Slide 1: Introduction This lecture is an introduction to iodometric and iodimetric titrations. We are going to see the differences between both of the methods, the reactions which are involved and the specific titrants for the two types of titrations. I will talk, you will listen During the lecture I will ask you some questions and at the end, you will do some tasks to check that you have understood the essential information. The tasks that you will do involve completing the same flow-charts which I will use in the talk.

2 Fact File 1: Introduction to iodometric and iodimetric titrations
Acid-base Standardization Chromatography Permanganimetric Gravimetry Redox Titrations Fajans Preciptation Complexometric

3 Fact File 1: Introduction to iodometric and iodimetric titrations

4 Fact File 1: Introduction to iodometric and iodimetric titrations
Slide 2: Titrations are one of the two types of Classical Quantitative Analysis. What is the other classical quantitative analysis? Exactly, the other classical quantitative chemical analysis is gravimetry. You will see gravimetry in other parts of the course. Let’s continue by asking about titrations. What are the four types of titrations? Yes, remember the four types are: Firstly, acid-base titrations, secondly complexometric titrations, thirdly precipitation titrations and fourthly redox titrations. Remember that we started working with acid-base titrations, then we moved on to complexometric titrations and finally we saw precipitation titrations. Today we will be looking at iodometric and iodimetric titrations, which are examples of redox titrations. We have left redox titrations until now, because you needed to be familiar with the other three type of titrations. So, let’s look at redox titrations in more detail. Do you remember other redox titrations that we have done in the laboratory? Yes, we have done other redox titrations like the determination of the percent of hydrogen peroxide and other ones. Now, we are going to look at the redox titrations involving iodine. Notice here that there are two types of redox titrations involving iodine. The most important thing in this presentation is for you to understand the differences between iodometric and iodimetric titrations. Both involve iodine, but as you will see there are some differences. The analysis that we will perform in the laboratory is the iodometric titration of cooper, which is a classical quantitative chemical analysis, a redox titration involving iodine. It is used because it is necessary to quantify copper in water, alloys, minerals and so on

5 Fact File 1: Introduction to iodometric and iodimetric titrations
Examples Acid-base Quantification of acetic acid in vinegar Complexometric Precipitation Redox Slide 4: Before we continue, let’s review what we mean by the word titration. A definition of the word titration is: A titration is a procedure in which volume increments of the known reagent solution-which is called the titrant- are added to the analyte until the reaction is complete. Does anybody remember the four types of reactions that we call fundamental analytical reactions? Exactly, the four types are acid-base, complexometric, precipitation and redox. How do we classify titrations? Remember, we classify titrations according to the type of reaction between the titrant and the analyte. As you can see from the diagram, the titrant is usually delivered from a buret. Do you remember in which titrations the titrant is in the Erlenmeyer flask? That’s right, the titrant is in the Erlenmyer flask in standardization titrations.

6 Fact File 1: Introduction to iodometric and iodimetric titrations
Examples Acid-base Quantification of acetic acid in vinegar Complexometric Quantification of chloride (Cl-) in water Precipitation Water Hardness (Calcium and magnesium) Redox Quantification of hydrogen peroxide (H2O2) Slide 4: Before we continue, let’s review what we mean by the word titration. A definition of the word titration is: A titration is a procedure in which volume increments of the known reagent solution-which is called the titrant- are added to the analyte until the reaction is complete. Does anybody remember the four types of reactions that we call fundamental analytical reactions? Exactly, the four types are acid-base, complexometric, precipitation and redox. How do we classify titrations? Remember, we classify titrations according to the type of reaction between the titrant and the analyte. As you can see from the diagram, the titrant is usually delivered from a buret. Do you remember in which titrations the titrant is in the Erlenmeyer flask? That’s right, the titrant is in the Erlenmyer flask in standardization titrations.

7 Fact File 1: Introduction to iodometric and iodimetric titrations
example Analyte Titrant Indicator Acid-base Quantification of acetic acid in vinegar Acetic acid (CH3COOH) Sodium hydroxide (NaOH) Phenolphthalein Complexometric Quantification of chloride (Cl-) in water Precipitation Water Hardness (Calcium and magnesium) Redox Quantification of hydrogen peroxide (H2O2)

8 Fact File 1: Introduction to iodometric and iodimetric titrations
Titration example Analyte Titrant Indicator Acid-base Quantification of acetic acid in avinegar Acetic acid (CH3COOH) NaOH (sodium hydroxide) Phenolphthalein Complexometric Water Hardness (Calcium and magnesium) Calcium and magnesium (Ca 2+ , Mg 2+) EDTA Eriochrome black T Murexide Precipitation Quantification of chloride (Cl-) in water Chlordie AgNO3 (silver nitrate) Mohr, Volhard, Fajans Redox Quantification of hydrogen peroxide (H2O2) Hydrogen peroxide (H2O2) KMnO4 (potassium permanganate) No indicator

9 Fact File 1: Introduction to iodometric and iodimetric titrations
Direct Titrations Indirect Titrations Back Titrations Iodometry

10 Fact File 1: Introduction to iodometric and iodimetric titrations
Example Type of reaction Acid-base Quantification of acetic acid in vinegar □ Direct Titration □ Indirect Titration □ Back Titration Complexometric Water Hardness (Calcium and magnesium) Precipitation Quantification of Cl in Water Mohr Method Fajans Method Volhard Method Redox Quantification of hydrogen peroxide (H2O2)

11 Fact File 1: Introduction to iodometric and iodimetric titrations
Example Type of reaction Acid-base Quantification of acetic acid in vinegar ■ Direct Titration □ Indirect Titration □ Back Titration Complexometric Water Hardness (Calcium and magnesium) Precipitation Quantification of Cl in Water Mohr Method Fajans Method Volhard Method □ Direct Titration □ Indirect Titration ■ Back Titration Redox Quantification of hydrogen peroxide (H2O2)

12 Fact File 1: Introduction to iodometric and iodimetric titrations
Direct titration analyte + titrant → product unknown known Example: Quantification of acetic acid in vinegar CH3COOH + NaOH → CH3COONa + H2O Slide 3: Until now, most of the titrations that we have performed in the laboratory are direct titrations. As you know, a direct titration involves one reaction between the analyte and the titrant. The reaction between the analyte and the titrant generates a product. You also know that an analyte is the substance being analyzed. In our case, the analyte is the substance that is being quantified. Now, in order to be able to quantify the analyte, we need the analyte to react with a substance of a known concentration. The substance of a known concentration is called the titrant.

13 Fact File 1: Introduction to iodometric and iodimetric titrations
There are a lot of redox titrations classified according to the titrant used. 1) Permanganimetric: Titrant KMnO4 2) Dichromatometric: Titrant K2Cr2O7 3) Titrations involving iodine (I2) Iodimetry Iodometry Titrations that create or consume I2 are widely used in quantitative analysis. Slide 5: As we saw in slide 2, we classify redox titrations according to the titrant which is being used. There are a lot of redox titrations and the most common ones are: First we have Permanganimetric redox titrations where the titrant is KMnO4 (Potassium permanganate). Then we have dichromatometric redox titrations where the titrant is K2Cr2O7 (Potassium dichromate). And finally the titrations that interest us today are the titrations involving iodine (I2). We divide these titrations into two types. Iodimetry –that is, i-o-DI-metry Iodometry – and i-o-DO-metry Notice that the two names are very similar; the objective of this talk is for you to learn the difference between the two types. As we said before titrations that create or consume I2 are widely used in quantitative analysis.

14 Fact File 1: Introduction to iodometric and iodimetric titrations
A reducing agent is the element or compound in a redox reaction that reduces another species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox. Examples of reducing agents: The active metals sodium, magnesium, aluminum, and zinc, NaH, CaH2, and LiAlH4, which formally contain the H- ion.

15 Fact File 1: Introduction to iodometric and iodimetric titrations
An oxidaizing agent is the element or compound in a redox reaction that oxidaizes another species. In doing so, it becomes reduced, and is therefore the element or compund that gain electrons. Examples: permanganate (MnO4-), chromate (CrO42-), and dichromate (Cr2O72-) ions, sodium hypochlorite (bleach) as well as nitric acid (HNO3), perchloric acid (HClO4), and sulfuric acid (H2SO4)

16 Fact File 1: Introduction to iodometric and iodimetric titrations
When a reducing analyte is titrated with iodine (the titrant), the method is called iodimetry. Iodimetry: A direct titration with only 1 reaction: analyte + titrant (iodine I2) → product (iodide I-) unknown known

17 Lecture 1: Introduction to iodometric and iodimetric titrations
When a reducing analyte is titrated with iodine (the titrant), the method is called iodimetry. Example: Quantification of Ascorbic Acid (Vitamin C) C6H8O6 + I2 → CçH6O6 + 2I- + 2H+ Iodine rapidly oxidizes ascorbic acid, C6H8O6 , to produce dehydroascorbic acid, C6H6O6 . Ascorbic acid Dehydroascorbic acid Pictures taken from:

18 Lecture 1: Introduction to iodometric and iodimetric titrations
Iodometry is the titration of iodine (I2) produced when an oxidizing analyte is added to excess I-(iodide). Then the iodine (I2) is usually titrated with standard thiosulfate solution. Iodometry: Not a direct titration because there are 2 reactions: analyte + I- → I2 unknown I2 + titrant (standard thiosulfate) → product Known Slide 7: Now let’s move on to iodometric titrations Unlike iodimetric titrations , in the iodometric ones two reactions are involved. Let’s analyze these two reactions. In this case the analyte is an oxidizing agent. Consequently, in the first reaction The analyte reacts with an excess of iodur to generate iode

19 Fact File 1: Introduction to iodometric and iodimetric titrations
Example: Quantification of Copper 2 Cu I- → 2CuI + I2 Analyte of unknown concentration I2 + 2S2O32- → 2I- + S4O62- Titrant -standrard solutions: sodium thiosulfate -known concentration

20 Fact File 1: Introduction to iodometric and iodimetric titrations
a) A reducing analyte b) One reaction c) Standard solution: Iodine (I2) Iodometric titrations: a) An oxidizing analyte b) Two reactions c) Standard solution: Sodium thisoufate Slide 8: To summarise the main information about iodimetric and iodometric titrations: In iodimetric titrations: The anlyte is a reducing agent. One reaction is involved. The standard solution is Iodine (I2) On the other hand in iodometric titrations: The analyte is an oxidizing agent. Two reactions are involved. The standard solution is sodium thiosulfate.

21 Fact File 1: Introduction to iodometric and iodimetric titrations
Analytical applications: Iodimetric titrations: Species analyzed (reducing analytes) SO2 H2S Zn2+ , Cd2+ , Hg2+ , Pb2+ Cysteine, glutathione, mercaptoethanol Glucose (and other reducing sugars) Section of a protein structure Source:

22 Fact File 1: Introduction to iodometric and iodimetric titrations
Analytical applications: Iodometric titrations: Species analyzed (oxidizing analytes) HOCl Br2 IO3- , IO4- O2, H2O2, O3 NO2- Cu 2+ MnO4-, MnO2

23 Fact File 1: Introduction to iodometric and iodimetric titrations
In this lesson: Iodometric titration of copper Sample: Copper wire (solid) First: Dissolve the sample copper wire Cu0 → dissolution → Cu 2+ Copper ion: oxidizing agent Second: Pre-treatment of the sample

24 Fact File 1: Introduction to iodometric and iodimetric titrations
Third: Iodometric titration 2 Cu I- → 2CuI + I2 Analyte of unknown concentration I2 + 2S2O32- → 2I- + S4O62- Titrant -standrard solutions: sodium thiosulfate -known concentration


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