# Winkler's method in the absence of iodide

I'm currently doing an IB chemistry individual investigation on the effect of adding bleach to water on the water's dissolved oxygen content. I've used Winkler's method for this and I'm just wondering whether it is possible to do Winkler's method without the presence of iodide ions $$(\ce{I-})$$, i.e. without adding chemicals like potassium iodide?

I used $$\ce{NaOH},$$ $$\ce{MnSO4},$$ $$\ce{H2SO4}$$ in this experiment (and $$\ce{Na2S2O3}$$ as the titrant) and I'm not too sure whether I used potassium iodide. However, I've obtained a result and found out a relationship where the dissolved oxygen content increases as I add more bleach into the water.

So my question is: is it possible to do a Winkler's method experiment without the presence of iodide ions? If so, could I know how my experiment worked?

• You shouldn't have used the winkler method for bleach analysis. Why not just stick to the iodine-thiosulfate method given in the textbook? Pg 421 in the Pearson HL book. – 124c41 Oct 22 '19 at 2:51

I used $$\ce{NaOH},$$ $$\ce{MnSO4},$$ $$\ce{H2SO4}$$ in this experiment (and $$\ce{Na2S2O3}$$ as the titrant) and I'm not too sure whether I used potassium iodide. However, I've obtained a result and found out a relationship where the dissolved oxygen content increases as I add more bleach into the water.