Iodine Adsorption and Titration with Na2S2O3

[charlie05]

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

 

[Borek]

This is rather chaotic, but some problems are easy to spot.

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).

 

[charlie05]

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...?

 

[Borek]

Yes, iodide is there mostly to improve iodine solubility (google triiodide).

 

[charlie05]

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