Question

n the experiment, you will be measuring the time it takes for the solution to turn blue. If you have initial concentrations of I^- = 0.016 M, BrO₃^- = 0.016 M, H⁺ = 1.8 x 10^-5 M, and S₂O₃^2- = 0.004 M, what is the concentration of I^- when the solution turns blue?

Answer 1

The equations that are involved

6I^-(aq) + BrO₃^-(aq) + 6H⁺(aq) → 3I₂(aq) + Br^-(aq) + 3H₂O(l)

I₂(aq) + 2S₂O₃^2- (aq) → 2I^-(aq) + S₄O₆^2-(aq)

Blue colour is got from the iodide

SInce the reaction is cyclic all S2O32- and BrO3- has to be consumed before I- is left

In the first cycle 0.016/6 moles of BrO3- is consumed along with 0.016 moles of I- to give 0.016/6 x 3 = 0.008 moles of I2

0.004/2 = 0.002 moles of I- is regenerated and the solution turns blue so the concentration of I- is 0.002 M