What is the molarity of a potassium triiodide solution, KI3 (aq), if 30.00 mL of the solution is required to completely react with 25.00 mL of a 0.500 M thiosulfate solution, K2S2O3 (aq)

The molarity is 0.203 M

Explanation:

Using the formula C (oxi) x V (oxi) / [C (red) x V (red) ] = N (oxi) / N (red)

Where oxi and red means reducing agent and oxidising agent respectively.

C = Concentration, V = Volume and N = number of moles.

C (oxi) = 0.5 M

V (oxi) = mL

C (red) = ?

V (red) = 30mL

Equation of reaction = 2K2S2O3 + KI3 = K2S4O6 + 3KI

so N (red) = 1, N (oxi) = 2

from the equation above,

C (red) = 0.5 x 25 x 1 / (2 x 30)

= 0.203 M.