iodine and sodium thiosulphate

Hey up

Im just finishing off my results for my chem course work at the moment and was wondering if you could help me. Im studying the rate of reation between iodine and propaoneone under acidic conditions. For one of my methods for determining rate i am using a back titration by quenching samples of the solution with sodium hydrocarbonate and then titrating with sodium thiosulphate. Just need help on 2 things really 1. how do i turn titra volume in to a concentration for sodiumthiosulphate and 2. will the cocentration of iodine be half of this due to its a 2 moles to one mole reaction. e.g. 0.0122 moldm sodium thio = 0.0061 mol iodine

I2 (aq) + 2S2O3 (2-) (aq) = 2I(-) (aq) + S4O6 (2-) (aq)
Also could some one confirm that what this website is explaining is the sodium thiosulphate to ioinde reaction

http://www.alevelchemistry.co.uk/Module_1/HTML_Pages/Redox/Iodine-Thiosulphate_titration.htm

Once again thanks for all your help

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