Question

The amount of I3–(aq) in a solution can be determined by titration with a solution containing a known concentration of S2O32–(aq) (thiosulfate ion). The determination is based on the net ionic equationGiven that it requires 41.4 mL of 0.450 M Na2S2O3(aq) to titrate a 30.0-mL sample of I3–(aq), calculate the molarity of I3–(aq) in the solution.

Answer 1

moles of Na2S2O3 = 41.4 x 0.450 / 1000

                               = 0.01863 mol

2S2O3^2-(aq) +   I3 - (aq) ----------------> S4O6^2- (aq) + 3 I- (aq)

According to the stoichiometry of the reaction:

moles of I3- = 0.01863   / 2 = 0.009315 mol

The molarity of the sample is               

Molarity of I3- = 0.009315 / 0.030 = 0.3105

Molarity of I3- = 0.311 M