The amount of i3-(aq) in a solution can be determined by titration with a solution containing a known concentration of s2o3^2-(aq) (thiosulfate ion).

the determination is based on the net ionic equation

2s2o3^2-(aq)+i3^-(aq) > s4o6^2-(aq)+31^-(aq)

given that it requires 35.8 ml of 0.350 m na2s2o3(aq) to titrate a 30.0-ml sample of i3^-(aq) calculate the molarity of i3^-(aq) in the solution

molarity of I3^-(aq) in the solution = 0.21 M

Explanation:

We are given the balanced chemical reaction and the volume and molarity of the  Na₂S₂O₃ so we can calculate the moles of the thiosulfate that were required, and then can calculate the molarity the  I₃⁻ by the definition of molarity.

First lets  convert the volume of Na₂S₂O₃ to liters:

35.8 mL x 1 L/1000 mL = 0.0358 L

# moles Na₂S₂O₃ = 0.350 mol/L x 0.0358 L = 0.0125 mol

From the stoichiometry of the reaction we know 2 mol Na₂S₂O₃ s react with 1 mol I₃⁻ , therefore mol of I₃⁻  will be given by

1 mol I₃⁻ / 2 mol Na₂S₂O₃  x 0.0125 mol Na₂S₂O₃ = 0.0063 mol  I₃⁻

and its molarity is:

0.0063 mol  I₃⁻ / 0.030 L = 0.21 M

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3