hello, I would like to know the method of preparation of wij's solution, who can help me please!
Wijs Reagent:
Dissolve 26.0 g of reagent grade resublimed iodine crystals in 2 L of reagent grade glacial acetic acid (99+%), heating gently if necessary. Cool to room temperature. Pipet 25 mL into a 250 mL flask. Add 100 mL purified water and titrate immediately with standard 0.1 N thiosulfate solution until the yellow iodine color almost disappears. Add 1 mL of starch indicator solution and complete the titration dropwise with vigorous swirling to the disappearance of the blue starch iodine complex. This is the original titer.
Remove 100 mL of the iodine solution (solution A), and store in a glass-stoppered bottle, for adjustment of the halogen ratio if necessary.
Dry chlorine gas from a cylinder by passing through a gas-washing bottle charged with concentrated sulfuric acid, and bubble the dried gas through a gas dispersion tube into the bulk of the iodine solution. Pass chlorine into the solution until the original titer is not quite doubled.
Check titer of reagent after chlorine addition by pipetting a 25.0 mL aliquot into 250 mL flask. Add 100 mL of distilled water, 10 mL of 30% potassium iodide solution, and titrate with standard 0.1 N thiosulfate solution as outlined in preceding paragraph. If original titer is doubled or greater, add a portion of iodine solution A and recheck. Store Wijs reagent in a glass-stoppered amber bottle. Prepare fresh reagent every 30 days.
Determination of Halogen Ratio in Wijs Reagent:
The halogen ratio (I2:Cl2) of the Wijs reagent shall be 1.10 ± 0.10. If the ratio is not in the prescribed range, add iodine or chlorine as required. The procedure for determining the ratio is:
Iodine Content:
Pour 150 mL of saturated chlorine water into a 500 mL flask and add some glass beads. Add 5.0 mL of Wijs reagent by pipet, shake and heat to boiling. Boil briskly for 10 mins., cool and add 30 mL of 2% sulfuric acid solution and 10 mL of 30% potassium iodide solution. Mix well, add 1 mL of starch indicator solution and titrate immediately with standard 0.1 N thiosulfate solution to disappearance of the blue starchiodine color.
Total Halogen Content:
Pour 150 mL of recently boiled purified water into a clean 500 mL flask. Add 10 mL of 30% potassium iodide solution. Pipet 20.0 mL of Wijs reagent into the flask and mix well. Add 1 mL of starch indicator solution, and titrate immediately with standard 0.1 N thiosulfate solution to disappearance of the blue starch-iodine color.
Calculate Halogen Ratio (I2 : Cl2):
= 2A / (3B- 2A)
where: A = Iodine content titer
B = Total halogen content titer
In the method, it is important that all volumetric measurements be made at the same temperature because acetic acid solutions have a large coefficient of expansion.
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