Question

A sample of a new cleaning product, "Joe's Famous Bleach Cleaner," with a mass of 54.0 g , was diluted with an acetic acid solution containing excess I−. A small amount of starch indicator solution was then added, turning the solution a deep bluish-purple. The solution was then titrated with 0.180 M sodium thiosulfate, Na2S2O3, containing the ion S2O32−. A volume of 41.0 mL of sodium thiosulfate, the titrant, was needed to turn the solution colorless.

What is the percentage composition by mass of NaClO in the bleach product?

Answer 1

NaOCl + 2 I-(aq) + 2H+ ----------> I2(s) + Cl- + H2O + Na+

I2 + 2S2O32- ----------> S4O62- + 2 I- ,

moles of thiosulphate used = 0.180 x 0.041

                                          = 0.00738 mol

moles of iodine reacted = 0.00738 /2

                                      = 3.69 x 10^-3 mol

moles of iodine produced = 3.69 x 10^-3

moles of bleach = 3.69 x 10^-3

mass of bleach = 3.69 x 10^-3 x 74.442 = 0.275 g

% of bleach in bleaching powder = (0.275/ 54) x100

                                         = 0.509 %