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Topic: copper sulfate + sodium carbonate = 2 different reactions  (Read 30268 times)

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Offline antimatter101

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copper sulfate + sodium carbonate = 2 different reactions
« on: July 08, 2013, 07:27:52 PM »
Once i reacted copper sulfate with sodium carbonate (double displacement) to get copper carbonate and sodium sulfate solution. There was a green suspension of copper carbonate in a clear solution of sodium sulfate.

This time i did the same reactions, and i got blue fluff in a clear solution... That was not supposed to happen! I checked google and there were multiple answers... sometimes it was green, sometimes the copper carbonate was blue, and some websites said that the copper carbonate had a colour change due to the presence of sodium ions. I have no way of verifying this. Help me somebody.


Offline Arkcon

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #1 on: July 08, 2013, 08:23:48 PM »
I suspect that the compound CuCO3 produced by the precipitation reaction of a soluble copper salt and sodium carbonate is a green solid, I'd seen it before.  The blueish solids mentioned are likely basic copper carbonate -- a mixed salt of CuCO3 and Cu(OH)2 formed by other reactions.  I don't know what the blue fluff you've found is, but when I used to do precip. reaction with my chemistry set as a kid, I'd often get a fluffy precipitate that changed colors as it aged.  Maybe some older chemistry texts have an explanation for the sort of odd precip. reaction you're getting.
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Offline AWK

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #2 on: July 09, 2013, 01:54:06 AM »
In water solution you never get pure CuCO3.
AWK

Offline antimatter101

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #3 on: July 11, 2013, 08:55:11 AM »
Okay, here is something even werider.

I filtered the mixture, after the blue precipitate had settled to the bottom. The filtrate was slightly blueish, and i thought that was the colour of the glass. (By the way, the filtrate is supposed to be sodium sulphate) Then i evaporated the filtrate and i got pale blue crystals, tiny crystals so that it looks like a powder. I have a sample of sodium sulphate at home. Its crystals are exactly the same size and shape as the ones i got, but they were clear, not blue. By the way, i had left the filtrate to stand for a long time and nothing condensed out of the solution. This means that the blue colour was present due to a soluble copper complex... and i have no idea what it is. This is really confusing me...

Pls help

Offline antimatter101

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #4 on: July 11, 2013, 08:56:46 AM »
Is copper carbonate and other related coordination compounds of copper II with water slightly soluble? That could answer my question. COpper carbonate is a tiny bit soluble, but not enough to colour my crystals blue, right?

Offline Borek

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #5 on: July 11, 2013, 12:42:57 PM »
All salts are soluble, even insoluble ones ;) It is just a matter of how concentrated the saturated solution is.
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Offline antimatter101

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #6 on: July 11, 2013, 08:41:47 PM »
I know that, but the question is: is copper carbonate soluble enough to colour my crystals, with a solubility product constant of 4x10-16. I have no experience with calculating problems such as these, since my course doesn't cover 'how to calculate the amount of impuritives by the colour it gives'.
« Last Edit: July 12, 2013, 02:29:58 AM by Borek »

Offline Borek

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Re: copper sulfate + sodium carbonate = 2 different reactions
« Reply #7 on: July 12, 2013, 02:31:27 AM »
Difficult to approach the problem not knowing the solution pH.

Even then it is not trivial.
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