Argentometry iodometry and iodimetry. Free pharmacy material. This titrimetric method is mainly based on the titrant used in the titration. The silver nitrate is used as the titrant which precipitates the subsequent halide.
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Argentometry iodometry and iodimetry. Free pharmacy material. This titrimetric method is mainly based on the titrant used in the titration. The silver nitrate is used as the titrant which precipitates the subsequent halide. This method is similar to that of the precipitation titrations. It is mainly used for the determination of the halides and halide compounds. The sample is mixed with the silver nitrate and forms the precipitate. In argentometric titrations, the sodium chloride is used as the primary standard for the standardisation of the silver nitrate.
Standard solution of the silver nitrate and the primary standard is prepared. Carry out the standardisation of the silver nitrate and calculate the normality of the prepared silver nitrate solution. Then the sample solution is prepared and the sample solution is titrated with the standard silver nitrate solution until the end point is obtained. The concentration of the sample solution is determined by the equation or by the titration curve.
Precipitate must be insoluble. Precipitate formation should be fast and rapid. Co-precipitation must be avoided. End point should be clearly visible. The end point in the argentometric titrations are detected by the following methods. Chemical method: By using the chemical reagent, the colour change is detected at the end point. These indicators are similar as that of the precipitation titrations. Chromate indicator: This method is named as Mohr's method.
Fluorescein indicator: This method is named as Fajan's method. Ferric solution: This method is named as Volhard's method. Potentiometric method: Potential difference between the silver electrode and a reference electrode is measured when immersed in the titration mixture.
Amperometric method: In this method, current generated between the pairs of silver microelectrodes immersed in the titration mixture. Current plotted as the function of reagent volume.
Accurately weighed silver nitrate is dissolved in the distilled water and made up to the required volume with the distilled water. To this solution, equal amount of the acetic acid and ethyl alcohol is added. To this, little quantity of eosin is added as the indicator and then the standard silver nitrate solution is titrated until pink colour is appeared. Less time consumption. Interferences are more. Care should be taken while preparation of silver nitrate solution. Used in the determination of the silver ores and alloys.
Used in the determination of halogens. Used in the determination of the mercaptans. Used in the determination of the fatty acids. Used in the determination of the zinc compounds. Method: Initially the zinc compound is precipitated with the precipitating agent.
Then the precipitate formed is dissolved in the mineral acid and is titrated with the excess of silver nitrate solution. Next the excess of silver nitrate is titrated with the ammonium thiocyanate using ferric ammonium sulphate as the indicator. Used in the sulphonamides determination. Method: An accurately weighed mg of the sample is dissolved in small quantity of NaOH. Then thymolphthalein solution is added to adjust the sample solution colour to blue. Then 50 ml of distilled water is added.
Then the blue colour is discharged with little quantity of sulphuric acid. To this, the silver nitrate is added until the black colour precipitate is formed. Collect the precipitate and acidify it with the nitric acid.
Then the excess silver is titrated with the ammonium thiocyanate by using ferric alum as the indicator. This method is used in the determination of the sulphadiazine, sulphamerazine and sulphamethazine.
These methods are widely used in the analysis of the compounds based on the reactions of the iodine. Iodine reacts directly and fastly for the determination of the compounds. The direct method is referred as iodimetry and the indirect method is referred as the iodometry. The main principle involved in the iodometry and the iodimetry titration is the oxidation-reduction reaction.
Example: Estimation of the vitamin C. In this method the reducing agent is titrated with the iodine solution. Iodine oxidises the sample. The end point is detected by the starch as indicator. Then, the iodine produced is back titrated with the help of an appropriate titrant like sodium thiosulphate. Thiosulphate is a strong reducing agent which is mainly used in the determination of oxidizing agents.
Starch is used as the indicator for both the reactions which produce intense blue colour for the iodimetry and the disappearance of the intense blue colour is the end point for the iodometry. Example: Determination of chlorites. Weigh 3. Stir the solution continuously to dissolve the iodine crystals and fill the required volume with the distilled water. Weigh mg of arsenic trioxide in a beaker and the 2 ml of sodium hydroxide solution is added. Warm the solution to dissolve the crystals. Then fill the required volume with distilled water.
Pipette out the above solution and acidify with the help of diluted HCl and little quantity of sodium carbonate is added to remove the excess of acid. The resulting solution is then titrated with the 0. The demerits of the starch indicator are as follows:. Insolube in cold water. Unstable in the water. It produces water insoluble complex with iodine. Hydrogen ion concentration: The hydrogen ion concentration increases the oxidizing power of the oxidizing agents.
Hence the hydrogen ion concentration is directly proportional to the oxidizing power of the oxidants. So it increases the iodine activity. The increase in the pH decreases the iodine solution activity that is oxidizing power. Loss of iodine due to its high volatility. Readily oxidised when exposed to the air. Used in the determination of the copper. Method: A known quantity of copper is dissolved in the nitric acid. The excess of nitric acid is removed by the addition of sulphuric acid.
Then pH of the solution is adjusted with the ammonium hydroxide. The end point is detected by the formation of the white precipitate. Used in the determination of the alkaloids. Method: Alkaloids are determined by the iodometric method. The alkaloid is dissolved in the alcohol and in the excess sulphuric acid. Then potassium iodide-potassium iodate solution is added and the liberated iodine is titrated with the 0.
The reaction is as follows:. Used in the determination of the chlorates. Used in the determination of the adrenaline. Method: Extract the drug with carbon tetra chloride and add starch solution and iodine solution.
Then sodium thiosulphate is added and finally sodium bicarbonate is titrated. Used in the determination of analgesics and antipyretics. Method: Sample is dissolved in acetic acid and water. To this, 0. The flask is stoppered and shake until the precipitate obtained.
Then dilute with water and allow standing for 30 min. Next filter the precipitate through glass-sintered filter. Take 50 ml filtrate which is titrated with 0. This method is used for the determinations of acetophenatidin, cinchophen and antipyrine.
Difference Between Iodometry and Iodimetry
The key difference between iodometry and iodimetry is that we can use Iodometry to quantify oxidizing agents , whereas we can use iodimetry to quantify reducing agents. Iodometry and iodimetry are two common titration methods useful in analytical chemistry. The basis of these two types of titrations is oxidation-reduction, and we can use it to determine redox species quantitatively. The basis of titration is a reaction between the analyte and a standard reagent known as the titrant. Moreover, we can use iodine for this redox titrations due to its capability of reacting fast with many species.
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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 Na 2 S 2 O 3.
Iodometry vs. Iodimetry
Iodometry, known as iodometric titration, is a method of volumetric chemical 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. Iodometric titration is used to find cl2 conc. Redox titration using sodium thiosulfate, Na2S2O3 usually as a reducing agent is known as iodometric titration since it is used specifically to titrate iodine.