From the balanced equations in the the chemistry section, it can be seen that 3 moles of I₂ are produced for every mole of IO₃^- reacted. And each mole of I₂ reacts with 2 moles of S₂O₃^2-. Therefore 6 moles of S₂O₃^2- are required to react with all the I₂ produced from 1 mole KIO₃^-.

The stoichiometric relationship of S₂O₃^2- to IO₃^- is:

The concentration of Na₂S₂O₃ can be calculated by:

Substitution of eqn 5 into eqn 4 gives eqn 6. This equations allows you to calculate the concentration of Na₂S₂O₃ from experimental numbers.

where:

• 214.00 g/mol is the molecular weight of KIO₃.
• 0.25000 L is the volume of the volumetric flask expressed in liters.
• vol KIO₃ is the volume of standard KIO₃ solution delivered from the buret.
• vol Na₂S₂O₃ is the total volume of Na₂S₂O₃ delivered from the buret.

Using the rules outlined in part 10 of the lab manual, the upper and lower limits can be calculated by:

where the uncertainty for:

• net wt KIO₃ = ±0.0010 g.
• net vol KIO₃ = ±0.10 mL.
• net vol Na₂S₂O₃ = ±0.10 mL.
• 250.00 mL class A volumetric flask = ±0.12 mL.

To determine if two concentrations can be averaged, the concentration from one run must fit between the upper and lower limits of the other run.