Hi,

I'm doing an expiriment to determine the average rate at which the hypochlorite concentration of bleach decreases with exposure to air.

I am adding weak sulfuric acid and pottasium iodide to a known volume of diluted bleach, and then titrating with sodium thiosulfate (which I have previously standardised) untill a colour change occurs (having added starch indicator close to the end-point.) I now have the data of the number of moles of sodium thiosulfate required, but I am unsure how to calculate the number of moles of sodium hypochlorite in the sample. Could someone please give me the ratio of thiosulfates to hypochlorites, and the equation(s) to show the ratio?

Any help would be appreciated.

Edited June 3, 201213 yr by Jaden

"2 S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2 I⁻"

"2H⁺ + OCl^- + 2I^- → I₂ + Cl^- + H₂O"

 

Therefore 2 moles of thiosulfate will neutralise 1 mole of bleach.

 

Don't forget to take into account bleach dilution (as in you added to a known amount of diluted bleach).

"2 S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2 I⁻"

"2H⁺ + OCl^- + 2I^- → I₂ + Cl^- + H₂O"

 

Therefore 2 moles of thiosulfate will neutralise 1 mole of bleach.

 

Thanks! That really helps.