percent transmittance

[gretel789]

Consider the following experiment. 20 ml of a 1.00M HCl solution is added to 100 ml of a 0.100ml of a 0.100 M aqueous solution of sodium thiosulfate. After 40 seconds, the reaction has produced enough sulfur to cause a decrease in the percent transmittance to 90%T. IF this reaction is repeated using 0.05M sodium thiosulfate, how long should it take for the reaction mixture to give a 90%T reading if the reaction is first order with respect to Na2S2O3??