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Thiosulfate Standardization via Iodate Titration

  1. Nov 21, 2012 #1
    1. The problem statement, all variables and given/known data
    How do I figure out the concentration of Thiosulfate in mol/L or g/L if I am only given the following:

    0.00167M Iodate (IO3-)
    10g of 0.00167M Iodate (IO3-) in Solution
    0.71266g of Thiosulfate necessary to titrate
    IO3- MW = 174.9027 g/mol
    Thiosulfate MW = 248.18 g/mol

    2. Relevant equations
    Molarity = moles/L
    IO3- + 8I- + 6H+ -----> 3I3- + 3H2O
    I3- + 2S2O3 -----> 3I- + S4O6

    3. The attempt at a solution
    Using 1g~1mL
    0.00167M IO3- * (0.01 L) * (3 mol I3 / 1 mol IO3) * (2 mol S2O3 / 1 mol I3) * (1 / 0.71266 mL) * (1000 mL / 1 L) = 0.1406M S2O32-
  2. jcsd
  3. Nov 22, 2012 #2


    User Avatar

    Staff: Mentor

    With the assumption 1g=1mL your result is correct.

    But: the density of 0.1406M sodium thiosulfate is not 1 g/mL, but 1.0163 g/mL. I am not convinced you are expected to use this number, but it definitely shows your final result is wrong by about 1.6%.
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