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Non Life Sciences => Chemistry => Topic started by: valeg96 on 21/02/2014 20:47:07

Title: How do i clean copper sulphate crystals contaminated with sulfur traces?
Post by: valeg96 on 21/02/2014 20:47:07
hello, I have about 1.5 kg of CuSO4 in crystals, not powder. It's contaminated with ventilated sulfur, the one who gave it to me used a dirty tool to measure it. How can i separate the two? If i put the CuSO4 in water, not necessarily dissolving it all, will it be enough for the sulfur to float? What if i dissolve it all and filter? Do you have any ideas? heating doesn't seem that clever, as it will most likely melt the particles on the crystals. Any ideas?
Title: Re: How do i clean copper sulphate crystals contaminated with sulfur traces?
Post by: chiralSPO on 21/02/2014 21:05:40
You can dissolve the copper sulfate in water and filter out the sulfur. (definitely safest, maybe easiest)

You might also have luck dissolving the sulfur (sulfur is quite soluble in carbon disulfide at room temperature, though this solvent is extremely flammable and somewhat toxic. toluene can also do the trick, but is a much worse solvent...)

If the crystals are very large, and the sulfur is well powdered, you can probably just separate the two with a screen (holes big enough for S, but too small for CuSO4) Wash it off with something that neither is soluble in (like ethanol).

Depending how much sulfur there is, you might also be able to burn it off. Copper sulfate doesn't decompose until it gets over 600 C (though it will dehydrate and turn white--just add water and it will turn blue again). Sulfur has a flash point just above 200 C, so it should be possible to pass hot air over the crystals, and convert the sulfur to gaseous SO2 (with small amounts and plenty of ventilation)