In fact, both these terms refer to different methods of using Iodine in titrations to determine the concentration of an analyte under investigation. They differ in their approach. Iodometry is an indirect titration method whereas iodimetry is a direct titration method. This is the main difference between Iodometry and Iodimetry. What is Iodometry As mentioned above, Iodometry is an indirect method. The technique of Iodometry is commonly used in experiments where the amount of oxidizing agents in a water body needs to be quantified.
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As the name implies, iodine is involved. The technique of iodometry is commonly used in experiments where the amount of oxidizing agents in a water body needs to be quantified. This makes it the most suitable method since hypochlorite or peroxide, found in bleach, is a strong oxidizing agent. The end point is determined using starch as indicator which forms a blue-black colour with iodine and fades to colourless when the reaction is complete.
Iodometry is the quantitative analysis of a solution of an oxidizing agent by adding an iodide which reacts to form iodine, which is then titrated. Iodometric titration is a method of volumetric analysis, a redox titration, where the appearance or disappearance of elementary iodine indicates the end point.
Note that iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant. Iodine can be used as an oxidizing agent in many oxidation-reduction titrations and iodide can be used as a reducing agent in other oxidation-reduction titrations.
Starch, a complex carbohydrate, forms a blue-colored complex with I3-ion. So, at the point where the I3- is consumed by the titration, the titration solution turns from blue to colorless. The starch indicator is added to the solution near the end of the titration, at the point where dilute iodine imparts a pale yellow color to the solution. There are two reasons why the indicator is not added at thebeginning of the titration when the iodine concentration is high.
First, a diffuse endpoint would result from the slow dissociation of the starch-iodine complex if a large amount of iodine wereabsorbed in the starch. Second, iodometric titrations are carried out in strongly acid media, asituation that promotes the reaction between oxidizing agents and iodide.
Unfortunately starch has a tendency to hydrolyze decompose in acidic media, destroying its indicator qualities. Sources of error The volatility of iodine is a source of error for the titration. This can be effectively prevented by ensuring an excess iodide is present and cooling the titration mixture. Strong light, nitrite and copper ions catalyzes the conversion of iodide to iodine, so these should be removed prior to the addition of iodide to the sample.
For prolonged titrations, it is advised to add dry ice to the titration mixture to displace air from the erlenmeyer flask so as to prevent the aerial oxidation of iodide to iodine. Cloudiness, a result of the formation of colloidal sulphur will indicate the decomposition of thiosulphate has occurred. In acidic solutions, the decomposition of thiosulphate is aided by bacterial attack.
Therefore, all water and glasswareused in the preparation of thiosulphate solutions should be sterilized to reduce the likelihood of bacterial attack, and the thiosulphate solution should be stored in a refrigerator to slow microbial growth. The thiosulphate solution should be discarded if any bacteria or mold growth is observed.
However, if the thiosulphate solution is prepared on the day it is used, these precautions can be neglected. During the titration, the analyte solution should be continuously stirred in order to prevent a local excess of thiosulphate from building-up. Finally, a large excess of iodide is added to the analyte solution to encourage the titration reaction to go to completion. Unreacted iodide does not interfere with the reaction, however iodide can be air-oxidized if the titration is not performed immediately.
Consequently, one should prepare only one analyte sample at a time, and the titration should be completed rapidly to minimize air-oxidation. In this method, excess but known amount of iodide is added to known volume of sample, in which only the active electrophilic can oxidize iodide to iodine. The iodine content and thus the active chlorine content can be determined with iodometry National Environmental Methods Index.
The level of sodium hypochlorite NaClO , the active ingredient in household bleach, is determined iodometrically by reacting it with an excess of iodide and then titrating the iodine produced with standard sodium thiosulphate.
Bleach, as the name implies, is a substance that will whiten. Commercial chlorine bleach will be at least 5. Other bleaches contain calcium hypochlorite Bleaching powder or peroxides. A small amount of sodium carbonate is added to keep the solution neutral or slightly alkaline and thereby stabilize it against decomposition to elemental sulfur.
Standardization of Sodium Thiosulphate Titrant The thiosulphate solution should be standardized and used on the day it is prepared. Adjust the volume to near the zero mark, record the initial volume to the nearest 0. Mix thoroughly. Prepare only one sample at a time. Titrate until the solution becomes a pale yellow colour.
The starch is not added until just before the endpoint is expected, because otherwise the high concentration of iodine produces a reddish colour that does not disperse at the endpoint. Calculate the average molarity and standard deviation of your Na2S2O3solution. Prepare each sample one at a time. Dilute to the mark with distilled water and mix thoroughly. Safety wears gloves, goggles should be worn to prevent contact with any of the solutions 2. The experiment should be carried out as quickly as possible Peroxide determination using iodometric titration should be similar to that of hupochlorite shown above since it is also a good oxidising agent.
National Environmental Methods Index. Geological Survey. Lide, David R. Mendham, J.
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 sodium thiosulphate solution Na2S2O3. 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.
Difference Between Iodometry and Iodimetry
As the name implies, iodine is involved. The technique of iodometry is commonly used in experiments where the amount of oxidizing agents in a water body needs to be quantified. This makes it the most suitable method since hypochlorite or peroxide, found in bleach, is a strong oxidizing agent. The end point is determined using starch as indicator which forms a blue-black colour with iodine and fades to colourless when the reaction is complete. Iodometry is the quantitative analysis of a solution of an oxidizing agent by adding an iodide which reacts to form iodine, which is then titrated. Iodometric titration is a method of volumetric analysis, a redox titration, where the appearance or disappearance of elementary iodine indicates the end point.
Basic principles[ edit ] Dilute solutions containing iodine-starch complex. The color above can be seen just before the endpoint is reached. To a known volume of sample, an excess but known amount of iodide is added, which the oxidizing agent then oxidizes to iodine. Iodine dissolves in the iodide-containing solution to give triiodide ions, which have a dark brown color. The disappearance of the deep blue color is, due to the decomposition of the iodine-starch clathrate , marks the end point.