Lion850
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Report on making cobalt tartrate
First attempt: was to react basic cobalt carbonate with hot tartaric acid:
5C4H6O6 + C2H6Co5O12 = 5C4H4CoO6 + 2CO2 + 8H2O
14.5g tartaric acid was dissolved in 200ml near-boiling water, giving a clear solution. 10g basic cobalt carbonate was then added in small portions.
Each addition caused bubbling as the carbonate dissolved, once bubbling stopped the next portion was added.
Once all added the solution was dark purple. Stirring was continued for 30 minutes. The result was a thick mess - is emulsion the correct word? I
added water to increase the volume to 800ml and stirred for an hour, then left overnight to see if anything settles out. But the next morning it was a
bigger mess, there was only 100ml or so of clear supernatant liquid and 700ml of thick emulsion. I gave up and dumped it in the waste container.
Second attempt: Double displacement between ammonium tartrate and cobalt sulphate:
(NH4)2C4H4O6 + CoSO4.7H2O = (NH4)2SO4 + C4H4CoO6 + 7H2O
- 10g CoSO4.7H2O in 30ml water, heat & stir to get a dark red solution, as below.
- 6.5g ammonium tartrate dissolved in 20ml water, clear solution.
- Add ammonium tartrate solution slowly to hot cobalt sulphate solution while stirring. Solution turned dark:
- And after a few minutes more stirring pink-red:
- Switch off heat the stirred for another 15 minutes, then stop stirring and let cool to room temperature. This was the result:
- The supernatant liquid was decanted and filtered. The same color ran through the filter, which made me suspect there is excess cobalt sulphate. The
pink-red ppt was then washed twice with 70ml portions of water by stirring, settling, and decantation. After the second wash the supernatant liquid
was nearly completely clear, see below comparison with the first filtered supernatant on the left and final filtered wash water on the right.
- Transfer product to funnel and wash with water in funnel.
- Squeeze product between filter papers and paper towels, thus was the damp product:
- Leave out on bench to air dry overnight. Next morning, outside in the sun under a steel dish for 3 hours. This was the final product after drying:
- 7.8g of dry soft pink-red powder in vial. This is slightly more than 100% yield. So it is either a hydrate or still retain some moisture (I see the
label is wrong - should be O6....will be corrected)
This is not the first time I use my cobalt sulphate and it ends up with the stoichiometry apparently not completely correct. The CoSO4 is supposed to
be a .7H2O and this is how I enter it into the stoichiometry app. But it is old and a mix or darker and very pale pink. I can only think that it must
have dehydrated a bit over the years and is now a mix of hydrates, thus overall lower than .7H2O. Meaning I put more CoSO4 into solution that I think?
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B(a)P
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Another nice experiment thanks Lion850! CoSO4.7H2O does readily loose water on exposure to dry air. Obviously if you have lost
water from your salt you have a higher proportion of CoSO4 in your reaction mix.
Chapter 14 of Mellor (in the SM library) has a great number of pages dedicated to CoSO4 and its hydrates. In this text the anhydrous salt
is described as a deep red colour. It is unlikely you have the anhydrous salt, but maybe the colour gets deeper the more water that is lost.
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j_sum1
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I am loving your work again Lion. 
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vano
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Very nice compound. I have one question. You always use a similar vial. How many compounds did you collect in the vial?
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Lion850
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Vano I bought 2 boxes = total 200 from these vials from a chemical supplier. They seem quite good, can also handle hot products (solids around 150C
causes no issues).
See below some sample photos of what I made over the last 18 months or so.
       
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vano
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thanks. That's what I wanted to see
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