Iodine Adsorption and Titration with Na2S2O3

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The discussion focuses on the preparation and analysis of an iodine stock solution and its interaction with activated carbon. A stock solution was created using 2.5424 g of I2 and 24.1525 g of KI, resulting in a concentration of 117.7 g/dm3 I2. After mixing 150 mg of activated carbon with 12.5 ml of this iodine solution, titration with Na2S2O3 revealed an equilibrium iodine concentration of 0.0544 mol/dm3. The amount of adsorbed iodine was calculated by subtracting the equilibrium iodine from the original iodine added to the activated carbon. The discussion highlights the importance of distinguishing between free iodine and total iodine present in the solution.
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1/ iodine stock solution: mixed 2,5424 g I2 and 24,1525 g KI and made up to 100 ml with water
2/ 150 mg active carbon is mixed with 12,5 ml jodine solution from point 1 /
3/ At equilibrium were performed filtration and titration with 10 ml of the filtrate with a volumetric solution Na2S2O3 ( conc. 0,075 mol/dm3) - consumption 14,5ml of solution Na2S2O3

Questions:
A/the initial concentration of the iodine solution before the test
B/equilibrium iodine concentration found during titration
C/amount of adsorbed iodine on the sample surface - iodine number...in mg/g
D/ an estimate of the specific surface area of the AC sample assuming a monimolecular layer. Each iodine molecule occupies an area of 0.21nm2.

ad A /iodine content in KI...126,9/166...76,4% of I
in 24,1525 g KI is 18,45251 g I
the amount of iodine in the stock solution...18,45251/2+2,5424= 11,77g I2
concentration of the iodine solution...11,77 g I2 in 100g of solution...117,7 g/dm3 I2...?

reaction of tittration: 2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I−(aq)

2 moles of thiosulfate react with 1 mol I2

consumption of thiosulphate...14,5 ml 0,075 mol/dm3 solution...0,0010875 mol of thiosulfate
equilibrium iodine concentration ...0,000544 mol I2 in 10 ml of the filtrate...0,0544 mol/dm3 I2
 
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This is rather chaotic, but some problems are easy to spot.

charlie05 said:
ad A /iodine content in KI...126,9/166...76,4% of I
in 24,1525 g KI is 18,45251 g I
the amount of iodine in the stock solution...18,45251/2+2,5424= 11,77g I2
concentration of the iodine solution...11,77 g I2 in 100g of solution...117,7 g/dm3 I2...?

You are confusing free iodine capable of reacting with with total iodine present in the form of iodine and iodide (and mostly inert in the context).
 
so in the solution of I2 in KI I have to count only with the concentration of the original I2?I don't have to count on the amount of KI?

concentration of the iodine solution...2,5424 g I2 in 100g of solution...25,424 g/dm3 I2...?
 
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Yes, iodide is there mostly to improve iodine solubility (google triiodide).
 
ad B/equilibrium iodine concentration found during titration ?

reaction of titration: 2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I(aq)

2 moles of thiosulfate react with 1 mol I2 consumption of thiosulphate...

14,5 ml 0,075 mol/dm3 solution...0,0010875 mol of thiosulfate

equilibrium iodine concentration ...0,000544 mol I2 in 10 ml of the filtrate...0,0544 mol/dm3 I2

ad C/

amount of adsorbed iodine = original amount of iodine - equilibrium amount of iodine during titration

the original amount of iodine added to the activated carbon:
12,5 ml of solution, concentration 25,424 g I2/dm3...0,3178 g I2...0,00125 mol I2
 
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