iodometri

Iodometric
Iodometric
The titrimetric iodometric analysis indirectly to substances that are oxidizing agents such as iron III / Fe (III), copper II / Cu (II). Iodometric titration can be used untukmenetapkan compounds having a lebihbesar oxidation potential than the iodine-iodide system or compounds that are oxidizing agents such as CuSO4.% H2O. On iodometric method, the sample will be reduced by oxidizing KI (potassium iodide) is excessive and will result in I2 (Iodine) which would then be in ttrasi by Na2S2O3 (sodium thiosulfate). Banyakknya volume of Na2S2O3 (sodium thiosulfate) was used as titrant equivalent to I2 (iodine) and produced equivalent levels of the sample. Standard solution used in the iodometric method is Na2S2O3 (sodium thiosulfate). Salt is usually shaped in the form of pentahydrate or Na2S2O3.5H2OLarutan not be distandaarisasi by weighing directly, but must be standardized with the standard primer.Karena Na2S2O3.5H2O unstable in the long-term storage. On iodometric method of examination should be kept stable pH (hydrogen pondus). Solution should be maintained at a pH of less than 8.Karena if the pH is more than 8 or in an alkaline I2akan react with hydroxide (OH-) to form the next hyphoiodit Iodides and iodide, and decomposes into Iodidat which can oxidize thiosulfate to run the reaction sulfat.Sehingga not quantitative. This method uses an indicator on Amylum 1%. Amylum have properties difficult to dissolve in water and unstable in water suspension to form complex compounds poorly soluble in water when reacting with iodium.Sehingga penanbahan Amylum as indicators should not be added at the beginning reaksi.penambahan Amylum as an indicator should be given towards the end point titration (at the time of pale yellow solution). Titration end point is marked with blue color changes into a clear solution (from blue to blue hilang.Jadi addition of starch is carried out as it approaches the titration end point is so that starch does not wrap as it will cause the starch iodine titrated difficult to return to the original compound. Process of titration should be done as soon as possible, this is due to the easy nature of I2 menuap. At the titration end point that is bound iodine also reacts with the titrant lost so suddenly disappeared and the blue color changes are very obvious. Use of this indicator is to clarify the solution color changes that occur at the end point titration. sensitivity of the color depends on the solvent used. iodine-starch complex has a small solubility in water, so it is generally added at the titration end point. If a solution of iodine in KI in the neutral atmosphere is titrated with sodium thiosulfate, then: -+ I3-3I-+ 2S2O32 S4O62- S2O32-+ I3-2I-+-S2O3I 2S2O3I-+ I-+ I3-S4O62- S2O3I-+-S4O62 S2O32-+ I-
Sodium thiosulfate (Na2S2O3.5H2O) can be easily obtained in a high state of purity, but there's always a little uncertain of the exact water content, has particularly karenaNa2S2O3.5H2O flouresen or decaying properties of the salt-cracked and unstable in the long-term storage. Therefore, these substances are not eligible to serve as the primary standard stock solutions. Sodium thiosulfate (Na2S2O3.5H2O) is a reducing agent, with the following equation: 2S2O32-S4O62-+ 2e- Standardization of sodium thiosulfate (Na2S2O3.5H2O) can be done using potassium iodate, potassium chromate, copper and iodine as the primary standard solution, or with potassium permanganate or cerium (IV) sulfate as the secondary standard solution. But in this experiment the compound used in the process of standardization of sodium thiosulfate (Na2S2O3.5H2O) is potassium iodate (KIO3) standards. Solution of sodium thiosulfate (Na2S2O3.5H2O) before being used as a standard solution in the iodometric process should be standardized in advance by potassium iodate (KIO3) which is the primary standard. Solution of potassium iodate (KIO3) iniharus added with concentrated sulfuric acid, the color of the solution became clear. And after adding the potassium iodide (I2), the solution becomes dark brown. Function of the addition of concentrated sulfuric acid (H2SO4 PA) in the solution is to give the acid, because the solution consisting of potassium iodate (KIO3) and klium iodide (KI) is in neutral or has a low acidity. His reaction is as follows: IO3-+ 5I-+ 6H + → 3I2 + 3H2O
Determination of levels of Cu2 + by Standard Na2S2O3 solution In the determination of Cu by standard Na2S2O3 solution will be some change in color of the solution before the titration end point. Pure copper can be used as a primary standard for thiosulfate and sodium thiosulfate should be recommended if it is used to determine copper. Standard pair potential Cu (II) - Cu (I) is +0.15 V and therefore iodine is a better oxidizing agent than the ion Cu (II). But when the iodide ion is added to a solution of Cu (II) will precipitate formed Cu (I). 2Cu2 + + 4I-2CuI (s) + I2 Determination of Cu2 + in solution with the help of a solution of sodium thiosulfate performed diluting 5 mL sample of the salt to 100 mL and taking 10 mL of dilution is to be added to a solution of KI 10%, and titrate with standard solution of sodium thiosulfate until the solution of the original dark brown to a solution of a pale yellow. Then the solution was added with 2 mL of 1% starch solution initially produces pale yellow to dark blue, addition of 1% starch indicator is intended to clarify the color changes that occur in the solution. then the solution is back titrated with sodium thiosulfate solution until the blue color of the solution right away. To further clarify the occurrence of the reaction, is added to a solution of I2 with starch amilum.Bertemunya this will cause any blue-colored solution kehitaman.Selanjutnya titration is continued until the blue color disappears and a cloudy white. I2 + I2-starch starch 2S2O32 + I2-starch-2I-+ S4O6 + starch- Things to consider after the addition of starch is the nature of the adsorption on the surface of the deposition of copper (I) iodide. These properties lead to the absorption of iodine and where iodine was removed by titration, the titration end point will be reached too quickly. Therefore, prior to the titration end point is reached, when the color of the solution is titrated with Na2S2O3akan changed from blue to clear, the addition of potassium thiocyanate KCNS. 

REFERENCES 

Basset.J etc. Festive 1994.Buku Vogel, Quantitative Analysis of Inorganic Chemistry. Book Medical Publishers EGC. Jakarta. Day RA. Jr. and Al Underwood.1992. Quantitative Chemical Analysis. Sixth Edition.: Erlangga.Jakarta Khopkar, S. M. 1990. Basic Concepts of Analytical Chemistry. University of Indonesia Press. Jakarta. Rivai, Harrizul. Of 1995. Chemical Examination of principle. Publisher UI. Jakarta.