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Science and thiosulphate

A few posts back someone asked.  I've been known to be wrong before, as
James can attest, but I think I have this one figured out.  Here it goes:

The neutralizing reaction of the thiosulphate ion with chlorine is given

2S2O3-- + Cl2  -----> S4O6-- + 2Cl-

Tap water typically will not have more than 1ppm chlorine at the tap, some
treatment plants aim for 1ppm Cl at the exit of the treatment plant so
that by the time it reaches your tap, there should still be a residual.
In North America, the 1ppm is often true, but I believe Europe uses a
lower level of chlorine at the exit of treatment.

I'll save you the math, if anyone wants it I can post it but the bottom
line is-

To neutralize 4.3 Liters of water containing 1ppm chlorine you require 1
mL of 0.12 molar thiosulphate.  (It's just that I had 0.12 M thiosulphate)

Julie De Merchant Ph.D. chemist
Guelph, Ontario