[lab123]

I've recently read an article called 'sulphur dioxide and tanin' by G.W.A Fowles. it talks about a titration between iodine and wine to determine the sulphur dioxide content. It gives this equation to work out the sulphur dioxide content in parts per million(ppm):

sulphur dioxide in ppm = 12.8* volume of iodine added(in cm3).

Does anyone know where does the value 12.8 come from?  

[Mitch]

This is the general formula for parts per million, but....

ppm = mass of the solute/ mass of the solution *10^6 parts per million

...If your density is approximately 1.0g/ml  you can just use this nifty trick
1ppm = 1mg/liter

Let me know if you need more info.

[lab123]

Hi! Can you show me how 12.8 is derived?

[Bystander]

"12.8" is a meaningless number without information on the volume being titrated, the reaction, and the strength of the titrant (I doubt very much that the analysis is being done with elemental iodine).

[hmx9123]

I used to TA a lab that actually calculted several things based on titration, including alcohol concentration and SO₂ concentration.  There were no 12.8 figures in there.  I'm sure that number came from the concentration & volume of the iodine solution used.  If you're interested, I can post the part of that lab that dealt with the sulfur dioxide concentration.

[AWK]

Concentration of iodine and volume of wine are always needed - then this number can be explained (probably concentration of I₂=0.1 M)