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Author: Subject: Making copper salts (especially basic copper carbonate)
Copper
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[*] posted on 4-1-2016 at 02:44
Making copper salts (especially basic copper carbonate)


Would the following methods work to produce their corresponding copper salts? Also
1. Should gentle heat be applied to dry the copper carbonate? (See below). Last time I tried I added way too much heat and everything melted (detailed in other thread)
2. Is a butane torch too much heat to decompose the basic copper carbonate? (See below)
3. Is evaporation the best route to remove the water from an aqueous solution of copper acetate? How long would evaporating 125 mL take? Copper acetate decomposes upon heating. Thanks

Copper Carbonate

Equation: 2CuSO4 + 2Na2CO3 + H2O -> Cu2(OH)2CO3 + CO2 + 2Na2SO4
CuSO4 pentahydrate M.W: 249.685
Na2CO3 M.W: 105.988
Sodium Carbonate Monohydrate M.W: 120.00
Basic copper carbonate M.W: 221.11

We want 150.00g of the basic copper carbonate, and that is 0.67839 moles. Therefore we need 1.35678 moles of sodium carbonate and copper sulfate. That equates to:
Copper sulfate Pentahydrate: 338.77g
Sodium carbonate monohydrate: 162.81g
Add 20% excess sodium carbonate: 195.37g

Method:
1. Weigh out 195.37g of sodium carbonate monohydrate in one weigh boat, and 338.77g of copper sulfate in another weigh boat.
2. Dissolve the copper in 2L of hot water, and the sodium carbonate in 1L of hot water.
3. Pour 1L of the copper sulfate solution into a 2L plastic beaker, and slowly add in total 500mL to the sodium carbonate, allowing effervescence to cease before continuing.
4. Using two coffee filters placed on top of each other, the solution is filtered and the filtrate is discarded. The copper carbonate is allowed to dry on the filter (funnel topped paper towel) for about 1 day.
5. Repeat steps 3-4
6. The copper carbonate is scopped out and placed on a dish and left to fully dry. (Should heat be applied?)
7. Using a mortar and pestle the copper carbonate is ground into a fine powder, and stored for future use.

Copper oxide
Equation: Cu2(OH)2CO3 -> 2CuO + CO2 + H2O
Around 160g of CuO results from 220g of basic copper carbonate.
To yield around 30g of CuO we use 40g of basic copper carbonate.

Method
1. 40g of basic copper carbonate is heated using a butane torch (is this too much heat?) until the mixture becomes totally black. It is stirred constantly using a glass stirring rod
2. The Copper oxide formed is stored for future use.

Edit:
The sodium carbonate M.W was 124 not 120 as I used in the calculations. The new correct figures are supplied below (thanks to aga for finding the error and calculating the correct figures)

338.74g of copper sulfate pentahydrate (difference of 0.03 probably due to significant figures in between calculations)
168.24g sodium carbonate
201.89g for 20% excess.

[Edited on 4-1-2016 by Copper]
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4-1-2016 at 06:13
blogfast25
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[*] posted on 4-1-2016 at 07:50


Quote: Originally posted by Copper  

Method
1. 40g of basic copper carbonate is heated using a butane torch (is this too much heat?) until the mixture becomes totally black. It is stirred constantly using a glass stirring rod
2. The Copper oxide formed is stored for future use.



A butane torch is hot enough but you need to heat the whole batch of carbonate through and through and for sufficient time to eliminate all traces of CO2 and water.

You method sounds OK but I haven't checked your numbers. As they say: 'measure twice to only cut once!'

[Edited on 4-1-2016 by blogfast25]




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[*] posted on 4-1-2016 at 09:02


Very nice post Copper.

It is rare that a question is posted with all the background checked out first.

I'll have a look at the numbers. Gimme a sec.




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[*] posted on 4-1-2016 at 09:51


One of my favorite ways of drying basic copper carbonate, after a thorough wash, the pale green slurry can be spread very thinly over a large window pane and left to dry (it will dry much much more quickly that way). Then you take a plastic or metal scraper and slowly scrape the Carbonate that will produce mostly a very thin dust and maybe a bit of very small flakes. Much less painful than grinding big chunks with a pestle and mortar.

- Bob




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[*] posted on 4-1-2016 at 09:56


Mostly looks pretty good. Nice work Copper.

Equation balances OK.

Think it is 124g/mol for sodium carbonate monohydrate.

I worked out that to get 150g product you need :-

338.74g CuSO4.5H2O
168.24g Na2CO3 = 201.89g for 20% excess.

At 20 C the solubility tables say the copper sulphate needs 1,056ml and the sodium carbonate needs 336ml of water to dissolve. Much less needed if Hot water is used.

The reaction will go ahead (i.e. thermodynamics are satisfied) however adding too much water will just slow it all down a lot (lousy kinetics) and make it bulky.

Process looks good.

You might save some time & filtering if the product (being insoluble) simply settles to the bottom, allowing you to decant off most of the water, then just spread it out, maybe shove it in the oven for a while if you're impatient.

Heating with a butane torch might knacker it : wiki says that basic copper carbonate decomposes at 290 C.

Don't forget to photograph the whole thing and post the results !

Edit:

Bob's suggestions are great ideas, especially the Washing part if you want clean product.

[Edited on 4-1-2016 by aga]




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[*] posted on 4-1-2016 at 11:00


An idea I have reading the above is that if the goal is CuO, there could be a more interesting less energy intensive approach which avoids the final thermal decomposition step.

My experience on heating Cu(OH)2, for example, is that it can splatter and get everywhere. The essence of the new idea is to look into preparations for Cu2O. Apparently, in moist open air conditions, the unstable red Cuprous oxide, Cu2O, naturally converts into the more stable black Cupric oxide, CuO.

One such path to Cu2O, for example, is described in a commercial patent "DECOMPOSITION OF COPPER SCRAP AND ALLOYS WITH COPPER AMMONIUM CARBONATE SOLUTIONS" by Patrick J. McGauley, available at http://www.google.com/patents/US2647829 .

The generally accepted copper chemistry involved is that an excess of metal Copper in the presence of a cupric salt can form a cuprous salt.

[Edited on 4-1-2016 by AJKOER]
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[*] posted on 4-1-2016 at 11:47


I've never had a problem with Cu(OH)2 spattering while heating (my students do it every year). Just make sure it's reasonably dilute, well-stirred, and that there's excess sodium hydroxide in solution. It doesn't need to boil to decompose.



Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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[*] posted on 4-1-2016 at 12:14


Quote: Originally posted by AJKOER  
Apparently, in moist open air conditions, the unstable red Cuprous oxide, Cu2O, naturally converts into the more stable black Cupric oxide, CuO.


No true. I have stable Cu2O and have also prepared it via Fehlings reduction (with glucose). It's stable and can even be calcined after aqueous precipation.

[Edited on 4-1-2016 by blogfast25]




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[*] posted on 4-1-2016 at 15:34


I'll attempt both syntheses pretty soon (likely near the end of this week), looking forward to posting the results here!

@aga - Thanks for the corrections and suggestions. I'll probably use 1000mL or less of relatively hot water to dissolve the copper sulfate. If I use less water I'm scared that it won't dissolve for a long time, as it often takes a very long time to make solutions that are close to saturation. Is it safe to microwave beakers with deionized water to very hot though? About the sodium carbonate, according to Wikipedia 50g of the monohydrate dissolves at 30c and solubility decreases after. So that would require around 600mL to be safe.

@blogfast25 - I'll probably stir and heat for quite a bit of time after it becomes fully black, to ensure it all decomposes.

@Arthur dent - I'll definitely wash the copper carbonate several times with distilled water in the filtration process to remove contaminants. However, I think that spreading it on a window pane may contaminate the copper carbonate.

@AJOKER and DraconicAcid - Copper (I) Oxide is another one I want to make, but probably after the easier ones (acetate, (II) chloride, (II) oxide, carbonate, chevreul's salt etc). Probably will use the glucose method though.

[Edited on 4-1-2016 by Copper]
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[*] posted on 5-1-2016 at 01:57


Those interested in making copper compounds should look for a procedure called "leeching". I don't have any references (could have been from Ullmann's Encyclopedia of Industrial Chemistry) but the process uses a mixture of ammonia and ammonium carbonate to leech metallic copper. Upon boiling it will precipitate carbonates, but unlike the direct precipitation of copper salts this reaction produces large particles. Anyone who has made copper carbonate knows what a mess it can be to filter out.

Edit: This process is also said to produce a uniform carbonate (not sure which one), while straight precipitation usually produces a random mixture of azurite and malachite depending on the conditions.

[Edited on 5-1-16 by Fulmen]




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[*] posted on 10-1-2016 at 14:26
Copper carbonate: success!


The process worked well, although I underestimated bubbling and lost a bit of yield due to overflowing. Filtration and washing worked well too (although I had to use 2 filters each because the residue was too heavy and broke through one filter). I let dry on filter paper, and now I have 4 filters filled probably 1/4 to 1/3 way full. 3 of the filters have green copper carbonate (relatively dry), but there is still definitely some moisture in the basic copper carbonate (it doesn't crumble when squashed, it deforms). The 4th filter has basic copper carbonate that is still blue [higher moisture content].

Once I grind everything up after it has dried, I'll post all the pictures :)
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[*] posted on 11-1-2016 at 03:45


Quote: Originally posted by Fulmen  


Edit: This process is also said to produce a uniform carbonate (not sure which one), while straight precipitation usually produces a random mixture of azurite and malachite depending on the conditions.



I'm sorry but that is simply not true and a persistent myth re. copper basic carbonate.

Straight precipitation using carbonate or bicarbonate produces malachite only.

Azurite is extremely difficult to prepare and despite many attempts on my part, one still ongoing, I've never succeeded.

Also, I've never had problems filtering precipitated malachite.

A lot of information about copper basic carbonates (malachite and azurite) can be found in this very long thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=50822

[Edited on 11-1-2016 by blogfast25]




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