Question

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 0.300 M thiosulfate solution, K2S2O3(aq)? The chemical equation for the reaction is 2 S2O32-(aq) + I3-(aq) → S4O62-(aq) + 3 I-(aq).

Answer 1

Answer:

Molarity of triiodide solution is 0.125M

Explanation:

According to balanced equation, 2 moles of $S_{2}O_{3}^{2-}$ completely react with 1 mol of $I_{3}^{-}$.

Moles of $S_{2}O_{3}^{2-}$ in 25.00 mL of 0.300 M of $K_{2}S_{2}O_{3}$ solution = $(0.300\times 0.02500)moles=0.0075moles$

So, 0.0075 moles of $S_{2}O_{3}^{2-}$ completely reacts with $(\frac{1}{2}\times 0.0075)moles$ of $I_{3}^{-}$ or 0.00375 moles of $I_{3}^{-}$

If molarity of $KI_{3}$ solution is S (M) then-

$S\times 0.0300=0.00375$

or, $S=0.125$

So, molarity of triiodide solution is 0.125M