Anayltical Chemistry: Molar Concentration

Question

For this question I keep getting 0.1775 but that is marked incorrect. It says you need to go to 4 significant figures so maybe I am rounding wrong? Thanks for the help.

Calculate the molar concentration of a thiosulfate solution from the following information:

A 35-mL aliquot of a 0.0217 M KIO₃ solution is added to a flask containing 2 g of KI and 10 mL of 0.5 M H₂SO₄. The resulting solution is titrated to a starch endpoint with 22 mL of the thiosulfate solution.

Molar Concentration ___

Answer 1

Hi Justin G.,

This is the third time I'm typing this, and I'm pissed at Wyzant for putting a new-page function key right next to the shift key, where it's so easy to hit it.

Anyway,

first write your balanced equation for: iodate + iodide +H+ = I2 + water,

and Iodine + thiosulfate = Iodide + S4O6(2-)

Determine which reagent is limiting, chase that through the two equations.

Now, your book? tells you to report(?) 4 sig figs, or does it imply to USE in your calc's?. to report, that's incorrect scientifically!

35 ml is exact (volumetric pipetting is very accurate!); IO3 is only 3 sigfigs;, the KI must be in excess?, since it's only 1 sigfig; and 22 ml is only 2 sigfigs. So, use all available precision, then report rounded to 2 sigfigs. That's what I would do, anyway.

-- Cheers, --Mr. d.