Use the chemical reactions shown below to answer the following questions. IO3- (

Question

Use the chemical reactions shown below to answer the following questions.
IO3- (aq) + 5 I- (aq) + 6 H+ (aq) 3 I2 (aq, brown/yellow) + 3 H2O (l)
I2 (aq, brown/yellow) + 2 S2O32- (aq) 2 I- (aq, colorless) + S4O62- (aq)

What is the stoichiometric relationship between IO3- and I2?

What is the stoichiometric relationship between I2 and S2O32-?

What is the stoichiometric relationship between IO3- and S2O32-?

How will knowing these relationships help you calculate the molarity of the Na2S2O3 solution in Part 1 of this experiment?

Explanation / Answer

Equation is balanced (checked)

IO3- (aq) + 5I-(aq) + 6H+(aq)----> 3I2(aq) + 3H2O (l)

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

Stoichiometric ratio between

IO3- vs I2

1 mol of IO3- is needed to form 3 mol of I2

therefore the ratio is 1:3

What is the stoichiometric relationship between I2 and S2O32-?

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

1 mol of I2 is needed to react with 2 mol of S2O3-2

Therefore, ratio is 1:2

What is the stoichiometric relationship between IO3- and S2O32-?

We need both ratios!

1 mol of IO3- ---> 3 mol of I2 ----> 3X2 mol of S2O3-2

1 mol of IO3-- ---> 6 mol of S2O3-2

Ratio is 1:6

How will knowing these relationships help you calculate the molarity of the Na2S2O3 solution in Part 1 of this experiment?

If you know this ratio, and you know how much IO3- you used, you may relate its mass/mol with respect of S2O3-2 ion, therefore 1:1 with Na2S2O3

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