Iodo-Iodimetry SMK Negeri 13 Bandung

PRINCIPAL Iodo-Iodimetry is Titration method envolving I2 and Iˉ Iodometry Reaction between oxidator with KI yields I2. The I2formed then titrated with Na2S2O3 standard solution. Iodimetry Titration reductor with I2 standard solution.

System of I2 ; I- E0 = +0.54 V I2 : iodin/iodium/iod haves the character of oxidator. Iˉ: iodide haves the character of reductor. If meets with strong oxidator such as K2Cr2O7, KMnO4, Cu2+ hence Iˉ will be oxidized become I2

The properties of I2 Solid matter blackest purple Middle oxidator, E0 + 0.54 Difficult to dissolve in water Sublimates at medium temperature Dissolves in Iˉ solution to form I3ˉsystem which has brown coloured. With amillum forms complex adsorption which has blue purple.

Two factors of causing the mistake I2 is easy to evaporate and difficult to dissolve in water Iˉ is easy to oxidized by O2 on the air

I2 is easy to evaporate and difficult to dissolve in water Solution: Titration quickly, decrease evaporation Provides good solvent Implication: Applies iod flask addition Adds excessive KI

Iˉ is easy to oxidized by O2 on the air Solution Titration in atmosphere non-O2, decrease contact with O2 Implication Applies iod flask addition Dissipates Oxygen in flask with producing CO2 from Na2CO3 and acid .

Secondary Standard Na2S2O3.5H2O Solid matter, white transparent Raveled to become Na2SO3 and Sulfur Decomposition quickened by temperature, light, acid and bacterium Reacts with I2 to become Na2S4O6 and Iˉ Reacts with O2 becomes SO42-

Preparation of Na2S2O3.5H2O Solution Boile water during 15 minutes, makes cool Weight out a number of Na2S2O3.5H2O Dissolves in cool water which has been boiled Adds Na2CO3 ( 0.2 gram/liter) Keeps in amber bottle minimum of 1 night. Filtered if needs Standardizes the concentration

Discussion Boiled of water needed to to dissipates CO2, O2 and kills bacterium CO2 can form acid with water so that pH solution declines. In thiosulphuric acid raveled to become sulphur and sulfite. And so do if there are bacterium Growth of bacterium Thiobacillus thiopharus is minimum at pH 9. pH 9 reachable with addition Na2CO3

Standardization of [Na2S2O3] Solution Primary standard which available K2Cr2O7, CuSO4.5H2O, KIO3, KBrO3 Secondary standard available KMnO4, I2

Standardization of [Na2S2O3] with K2Cr2O7 Heat K2Cr2O7 pa. at temp 110-1500C during 1-2 hours. Cool in exicator. Weight out accurately of 1.25 grams K2Cr2O7 then dissolves in volumetric flask of 250mL. Transfer by a pipette 25 of mL in to an erlenmeyer flask, add 1 gram KI and 5 mL HCl 2 Nitrogen . Shakes and lets 5 minute in dark place. Titrate with Na2S2O3 solution until colour of I2 is pale. Add 5 mL amylum 0.1 % Continue the titration until discoloration blue disappeared accurately. Calculate concentration of Na2S2O3

Reactions Cr2O72- + 6I- + 14H+ → 3 I2 + 2Cr3+ + 7H2O I2 + S2O32- → 2I- + S4O62- I2-amil + S2O32- → 2I- + S4O62- + amil blue tb tb tb tb Mek I2 = mek Na2S2O3 Mek I2 = mek K2Cr2O7 Hence, mek Na2S2O3 = mek K2Cr2O7

Discussion HCl is better for acidify the solution because the green colour of CrCl3 is clear, while Cr2(SO4)3 has bluest green colour. Reaction between dichromate with iodide taken place rather slow, so it must be let formerly for few minutes.

Discussion Addition of amilum is done when concentration of Iodine have been low because at high concentration iodine will form complex iod-amilum which is clotty and difficult to react with thiosulfate so that the end point is difficult to be reached.

Detection of The Equivalence Point and The End Point I2 in Iˉ has brown colour. Lower its concentration, more pale its colour. Thereby loss of I2 can be detected from its colour, but our eye have unable to see pale brown / yellow colour at concentration of 10-5 M. Blue colour of Iod-amil still be stand-out at concentration of 10-7 molars.

Discoloration at The End Point blue disappeared exactly Because of I2-amil is precise reacts with Na2S2O3

The Other Indicators Organic solvent like : Carbon tetrachloride (CCl4) and CHCl3 In both solvents above I2 dissolved forming purple solution Difficulty from usage of organic solvent as indicator is this solvent has BJ > BJ water, so that will reside in bottom of titrat solution.

Determinations of Iodo-Iodimetry Determination of Vitamin C Determination of Cu Haen Method Bruhns Method 3. Determination of Cl2 free from kaporit

Determination of Vitamin C Weight out of 20 sample tablets, broken, calculated weight of every tablet. Weight out number samples which contain of ±250 mg of ascorbic acid. Dissolves in Erlenmeyer flask, add 2 ml amilum 1% + 20 ml aqua demineralization ( if needs), titration with I2 standard until the end point. How its(the discoloration at the end point? Writes down the equation of the reaction! How to calculate ascorbic acid content in the sample?

Determination of Cu Haen’s Method Weight out accurately of 6.5 grams of sample Cu2+ , dissolved and rinsed with aqua demineralization and dilute sulphate acid. (what Is the function of dilute sulphate acid?), diluted it in volumetric flask 250 ml. Pipette 25 ml, put it into erlenmeyer flask + 5 ml H2SO4 4N + 1 g free KI of iodat, shakes. Titration with Na2S2O3 standard + amilum after closing to the end point, titration until reaching of the end point. What is the discoloration at the end point? Writes down the equation of the reaction! How to calculate the content?

Bruhns Methode Determination of Cu 6.5 grams Cu2+ sample dissolved and rinsed, diluted in volumetric flask 250 ml. Pipette 25 ml, put it into Erlenmeyer flask+ 5 ml H2SO4 4N + 1 g free KI of iodat + 5 ml KSCN 10%. Titration with Na2S2O3 standard + amilum after closing to the end point, titration until reaching of the end point. What is the discoloration at the end point? Writes down equation of the reaction How to calculate the content? What Is the difference between methods of Haens and Bruhns?

Determination of freeCl2 from Caporit 1.5 g sample is made by pasta, suspension, rinses and diluted with aqua demineralization in volumetric flask 250 ml + ether if there are effervescences. Pipette 25 ml + 1.5 g free KI of iodat + 5 ml HCl 5N, cover the flask, shakes. Titration with Na2S2O3 standard + amylum after closing to the end point, continue the titration until reaching of the end point. How is the discoloration at the end point? Writes down equation of the reaction! How to calculation Cl2 content in the sample?