chemkid - 20-6-2008 at 12:53
I tried a few experiments with this today. I have read woelen's experiments as well as those at http://www.crscientific.com/article-redox3.html
and a few others. I have gotten different results then all of them. I used reasonably pure reagents, definitely not technical grade. First i mixed
equal volumes of .5M sol of copper sulfate with .5M solution of sodium thiosulfate. After a few hours a yellow precipitant, as other have observed,
formed. But unlike what woelen observed, upon agitation the compound dissolved to form a yellow solution. Woelen mixed sodium thiosulfate and copper
sulfate as solids and added water to get this yellow compound.
Next, i did the same thing, but added an excess of thiosulfate. After many hours a white precipitant which is insoluble in additional water formed. I
used anhydrous sodium thiosulfate and copper sulfate pentahydrate. Any insight?
Chemkid
chemkid - 22-6-2008 at 09:49
Alright, update. After several days the equal volume and equal molar solutions formed a brown precipitate which has been established to be copper
sulfide.
woelen - 22-6-2008 at 11:22
This is a very interesting, but also rather complex reaction. Your results may look inconsistent with my results, but this is common with this
reaction. The exact outcome of this reaction strongly depends on the amounts and concentrations, and probably also on temperature.
I suggest you play around a little bit with this reaction. Another interesting one is the reaction between ferric ions (e.g. from ferric sulfate or
ferric chloride) and thiosulfate. Ferrous ions do not show such an interesting reaction.