Subcomputer
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CoCO3 + CuSO4 + H20 -> ?
I was attempting to do a replacement reaction in order to produce cobalt sulfate. A solution of copper sulfate dissolved in water was produced, then
finely powdered cobalt carbonate was added. The mix was then agitated until no more purple from the CoCO3 could be seen, and a light blue substance
(presumed to be CuCO3) began to precipitate.
This is where things became mysterious. I should have had a light blue-green precipitate and a red/orange solution, I have a slightly darker blue than
normal precipitate (compared to CuCO3 made with other methods) with larger grains, and a lightly colored indigo solution.
It's been 11 years since my last chemistry class, so I'm not asking for the answer, I'm asking to be taken through the steps to finding the answer so
I can apply them as "hands on" examples to what I'm reading in my chemistry books.
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Random
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maybe some double salt?
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woelen
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I do not expect any reaction at all or at best a very incomplete reaction. This is not the way to obtain cobaltous sulfate.
If you want a soluble cobaltous salt from CoCO3, then you need to add the carbonate to some dilute acid (e.g. 10% H2SO4). Use a slight excess of the
carbonate and keep on heating (not boiling!), until the formation of bubbles stops. Then allow the excess CoCO3 to settle at the bottom. The clear
liquid above the solid CoCO3 is a solution of the pure cobaltous salt, possibly with a small amount of left over acid.
[Edited on 24-3-13 by woelen]
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vmelkon
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That's not how you should do a displacement reaction.
You don't sprinkle solid CoCO3 into a solution.
1. Prepare a solution of CoCO3 in another beaker.
2. Prepare a solution of CuSO4 in another beaker.
3. Add 1 solution to the other.
Als, CoCO3 is relatively non soluble. But still, it is slightly soluble, just like CuCO3, so there will be a equilibrium reaction and you'll have some
CoCO3/CuCO3 as solid and CoSO4/CuSO4 as solution and a tiny amount of CoCO3/CuCO3 in solution.
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Subcomputer
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It appears part of my problem was improper molarity calculations. I added more CoCO3 and continued to agitate, the amount of light blue precipitate
grew. Finally I am left with an orange/red solution that I am presuming is CoSO4, and some unreacted CoCO3 that settled with the CuCO3 precipitate
when agitation ended.
I would have used H2SO4 but didn't have it available, this was a case of seeing what I could make with what I had.
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woelen
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A pure CoSO4-solution is not orange, it is pink/red. Probably you still have copper contamination in the solution. The blue color makes the color of
the total solution shift from red to more yellowish colors.
I am surprised though that you obtained the result you have now. I expected much less of a reaction. How fast is the reaction? Did it take hours, or
just minutes?
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Subcomputer
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I would say about 15 minutes of agitation the first time, then another 15 minutes the second. That's not exact, as each time after I saw a quite
visible (and fast) shift in color about 7-10 mins in I then continued agitation to try to get as much out of the reagents as I could.
I didn't use any form of heating, in fact showing how preliminary my lab is, the reaction was performed in a tightly sealed mason jar shaken by hand.
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