Can u answer this question?

Question

ok here goes:

3.335 g of iodine and 5 g of potassium iodide were dissolved in 200.0 mL of water. (The iodide ions are there simply to help the iodine dissolve). A 20.00 mL portion of this solution is reacted with 17.70 mL of sodium thiosulfate solution. Calculate the concentration of the thiosulfate solution.

I never learned concentration, so I need ur help. If you give me the answer and explain, tht would be great

Thanks!

Answer 1

I did a experiment similar to this. The only way I know of to calculate the concentration of thoisulfate is by the use of stoichiometry. Stoichiometry is basically using mole ratios to determine the amount of substance there is. To determine the mole ratio you need a chemical equation. The equation of this reaction is:

I2(aq) + 2S2O32-(aq)  --> 2I-(aq) + S4O62-(aq)

We can assume that all of the thiosulfate ion reacts completely (so none is left) with the Iodine. A certain amount of iodine reacts with a specific amount of thiosulfate. So from this you can determine the concentration of the thiosulfate. First lets determine the concentration of the 200mL iodine solution.  

3.335g of I *(mole/127g) *(mole/.2L) = .1313M of I

Next we can find out how much thiosulfate reacts with the portion of Iodine.  

.02L of I *(.1313mole/L) *(2mol S2O32-/1mol I2) * (mole/.01770L)= .2967M of S2O32-(aq)

Answer 2

oops not for me i suppose...

Answer 3

Well, TC, we will have to read something into the problem; the 17.7 mL of Na2S2O3 is sufficient to react with all the iodine in solution.  I don't know off-hand the reaction: probably iodine is reduced to iodide and the thiosulfate is oxidized to SO4=.

If you write it out, you will have the moles of Iodine and Na2S2O3 involved.  You find the conc of I2 in solution by dividing 3.335 g by the mole wt of I2.  That give you moles in 200 mL.  You use 10% of that, so that gives you the moles of I2 in reaction.  

From your reaction, you find the moles of thiosulfate needed.  Then concentration of thiosulfate= moles needed/17.7 mL