why is sodium thiosulfate readily soluble in water? how can a large amount of it be dissolved into only 3 ml of water?

Answer 1

First, most sodium salts are soluble in aqueous solution. Second, you don't say if you are using Na2S2O3 or Na2S2O3.5H2O NOR what you mean by "large amount."

Answer 2

I am using Na2S2O3.5H2O. By large amount i mean about 15 grams