IODIMETRIC TITRATIONS When an analyte that is a reducing agent (like hypo) is titrated directly with a standard iodine solution, the method is called “iodimetry”. involve the potentiometric titration of aqueous iodine with sodium thiosulfate the analyte (a reducing agent) reacts with iodine to produce iodide: iodimetry. Titrations Fajans Preciptation Complexometric. Fact File 1: Introduction to iodometric and iodimetric titrations. Quantitative Classical Chemical Analysis. Titrations.
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Iodometry – Wikipedia
Iodometry is used to determine the concentration of oxidising agents through an indirect process involving iodine as the intermediary. In the presence of iodine, the thiosulphate ions oxidise quantitatively to the tetrathionate ions. To determine the concentration of the oxidising agents, an unknown excess of potassium iodide solution is added to the weakly acid solution.
The iodine, which is stoichiometrically released after reduction of the analyte, is then titrated with a standard iodimetrif thiosulphate solution Na 2 S 2 O 3. Titration involving iodine commonly uses a starch suspension as indicator.
This suspension is a watery solution of starch with a few drops of bactericide added to prevent decomposition, as this would stop the starch behaving as an indicator. Once the bond between the iodine I 2 and the helical chain of beta-amylose is formed it turns an intense blue.
Colour of the starch solution in the presence of I2. In the presence of I- ions the starch solution is colourless.
Istituto comprensivo di Tubirgo. Iodometric titration needs to be done in a weak acid environment which is why we need to remember that:. Sodium thiosulphate needs a neutral or weak acid environment to oxidise with tetrathionate in an alkaline solution we would get sulphate oxidation.
In the food industry, iodometry is widely used to determine the concentration of hydroperoxides in any given lipid matrix oils and fats for human consumption. Oxidation is a chemical process which is catalysed by various factors presence of oxygen, levels of unsaturation in the oil, presence of metals, temperature and leads to the formation of hydroperoxides.
Determining the concentration of these chemicals is important because hydroperoxides have a negative iodometrric on the acceptability of the fat matrix used, and on the food fried in it, and they also decompose easily, forming molecules which are dangerous for human health.
Reaction of radicals responsible for formation of hydroperoxides in edible fats and oils. LH is a monosaturated or polyunsaturated acid. Hydroperoxides in the presence of KI reduce as shown in the redox reaction below. The reaction is illustrated as the sum of the two half-reactions in fig.
The iodine released is titrated using sodium thiosulphate at a known concentration with a starch indicator blue colour. The number of equivalents of titrated iodine is the same as the number of hydroperoxides present in the sample as shown in the reaction in fig.
Thiosulphate is added until the blue colour disappears and the solution turns colourless. The turning point indicates that all the iodine released has been titrated. GEASS ; titgations flask, source: Wikipedia ; erlenmeyer flask source: Fisher Scientific; beaker, source: The term iodimetry, on the other hand, refers to titration using an iodine solution and is useful for determining substances that have reducing properties.
The half-reaction is as follows:. Standard iodine solutions are of fairly limited use compared to oxidants because of their small electrode potential. One interesting application of iodometry iodojetric the food industry is for determining sulphur dioxide SO 2 in wine. Once sulphur dioxide is added to wine it does not remain free but oxidates in part and in part combines with other molecues:.
The free form either as a gas or an acid is the most important because it inhibits the action of microoganisms and acts as an antioxidant. Oxidated sulphur dioxide appears in the form of sulphur trioxide SO iodomettricsulphuric acid or potassium bisulphate.
The SO 2therefore, can combine with sugars, proteins and polyphenols. Combined sulphur dioxide is in equilibrium with the free form.
Difference Between Iodometry and Iodimetry
This means that any reduction in the free form will result in a significant quantity of the combined form moving towards the free form. Thi is another of the advantages of using sulphur dioxide because it guarantees the stability of the product over time.
The total sulphur dioxide titrationd the wine sample is determined through direct iodimetric titration using starch as the indicator. The titration reaction can be represented as:. The addition of an excess of I 2 makes the solution turn dark blue indicating that all the sulphur dioxide in the sample has been titrated. With red wines it is difficult to see the titrrations point because their intense red colour makes it difficult to perceive the colour change in the indicator.
Difference Between Iodometry and Iodimetry
Wikipedia ; burette, source: Steroglass ; ring line, source: Istituto Magistrale “Leonardo da Vinci” di Alba. The analytical chemistry laboratory. Safety in the laboratory. Neutralisation titration – part two. Optical methods of analysis. Treatment of experimental data. Important considerations Iodometric titration needs to be done in a weak acid environment which is why we need to remember that: Sodium thiosulphate needs a neutral or weak acid environment to oxidise with tetrathionate in an alkaline solution we would get sulphate oxidation ; 3.
Iodometri a strong acid environment thiosulphate decomposes to S 2 ; 4. In acid environments the iodide is oxidised to iodine as in the reaction below: Application of Iodometry In the food industry, iodometry is widely used to determine the concentration of hydroperoxides in any given lipid matrix oils and fats for human consumption.
Principles of method Hydroperoxides iofimetric the presence of KI reduce as shown in the redox reaction below. Performing the titration Scales, source: Iodimetrjc the titration cont.
Iodimetry The titartions iodimetry, on the other hand, refers to titration using an iodine solution and is useful for determining substances that have reducing properties.
The half-reaction is as follows: Titrationss of iodometry One interesting application of iodometry in the titrqtions industry is for determining sulphur dioxide SO 2 in wine.
Sulphur dioxide has several important functions: Forms of SO 2 in wine Once sulphur dioxide is added to wine it does not remain free but oxidates in part and in part combines with other molecues: Principles of the method The total sulphur dioxide in the wine sample is determined through direct iodimetric titration using starch as the indicator.
The titration reaction can be represented as: Carrying out the titratiohs 1 Erlenmeyer flask, source: Carrying out the titration 2. Formula for the determination of sulphur dioxide.
INTRODUCTION TO IODOMETRIC AND IODIMETRIC TITRATIONS
Le lezioni del Corso 1. The analytical chemistry laboratory 3. Safety in the laboratory 4. Inorganic qualitative analysis 5. Neutralisation titration – part two Oxidation reduction titration Iodometry and Iodimetry Instrumental Chemical Analysis Optical methods of analysis