cobalt_catalyst
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Separation of copper sulfate and sodium sulfate?
I recently made some copper sulfate by electrolysis using sodium bisulfate in place of sulfuric acid. The electrolysis was successful but now I am
left with a blue solution of copper sulfate and sodium sulfate. What would be the best way to separate the two? Would simply recrystallization
suffice?
Cogito Ergo Sum
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blogfast25
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Quote: Originally posted by cobalt_catalyst  | | I recently made some copper sulfate by electrolysis using sodium bisulfate in place of sulfuric acid. The electrolysis was successful but now I am
left with a blue solution of copper sulfate and sodium sulfate. What would be the best way to separate the two? Would simply recrystallization
suffice? |
Not easy. Both sulphates are well soluble. That's why sulphuric acid is used instead of Na bisulphate.
Chemical separation is probably needed here.
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Hexavalent
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Add sodium carbonate to a solution of your mixture, and filter off the copper carbonate that forms as a precipitate. You can then treat this with
whatever acid you choose to obtain a soluble copper salt.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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12AX7
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Assuming you've neutralized the pH (which should be around 4 or 5, I would guess), so there's no excess sodium bisulfate remaining, one of these
should work:
1. Crystallize the entire solution. Collect the granular product, load it into a filter funnel. Heat until the sodium sulfate decahydrate melts, 80
or 90C I believe, and allow it to drain (better yet, use vacuum).
A moist environment (but not steam) will facilitate this process, preventing the sodium sulfate from drying out so quickly. It could be done in a
double boiler, with a covering rag to trap some warmth.
2. Concentrate the solution until about half has precipitated. Heat to a gentle boil until all sodium sulfate dissolves; drain the remaining copper
sulfate (which is less soluble at high temperatures, though a lot will dissolve in the process). Cool the supernatant (separate the sodium sulfate
which precipitates below 80C if possible), dehydrate further and repeat.
3. Crystallize the entire solution. Try to do it slowly, to get large crystals of everything. Allow the cake to continue dehydrating at a
temperature below 80C. Sodium sulfate decahydrate crystals will slowly decompose into powdery anhydrous sodium sulfate, which can be sifted from the
(still very sharp and solid) copper sulfate pentahydrate crystals.
Note: copper sulfate pentahydrate also dehydrates in a similar manner, but it tends to leave a translucent to opaque, sky-blue pseudomorph, rather
than crumbling to dust as sodium sulfate does.
Tim
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