Cleanup from 'Making Copper Sulfate' (from Copper (II) Oxide + Sulfuric Acid)

Hello,

I know this practical has been discussed previously, but my question in slightly different.

I've heard recommended that the copper sulfate crystals made during this practical can be recycled. Assuming the students do indeed add copper (II) oxide in excess and allow it to react fully with the acid, I see no problem with this approach. However, if they do not heat the solution enough and/or make sure they've added the oxide in excess, surely the resulting crystals will be contaminated with concentrated sulfuric acid (once all the water has evaporated)?

Is the only was around this is to collect all the student's crystals, dissolve them, and add further copper (II) oxide/warm until the solution is no longer acidic then crystallise/filter? Or perhaps the crystals could just be washed with distilled water since the crystals themselves will only contain Cu(+2) and SO4(-2) ions?

Would love to hear other peoples' thought on this and am very happy to be corrected!

Thanks in advance.
 
Copper oxide is insoluble in water, when the students filter their samples through filter paper any remaining oxide should be left behind. Some student do poke holes through their filter paper if it filters too slow so you may wish to refilter them again if you are very concerned. Since the copper oxide is used in excess their should be little to no acid left.

We have a core colorimetry experiment that tests the purity of a sample of copper sulphate so we use the student made stuff for that.
 

clairelucas

COMMITTEE
Judging by the amount of copper oxide left on their filter papers, I would be surprised if they weren't consistently adding excess. But maybe a dip of UI paper would tell you, when redissolving, before adding to the stockpot..?
 
Thanks everyone! I have used UI paper previously and found the collected crystals + water I rinsed them with to be acidic.

I presume this was because the method we used involved only a slight excess of copper oxide (cleapss method) and the solutions weren’t heated strongly enough for the reaction to go to completion and consume all of the acid prior to filtration.
 
If this is the method using 1.4M H2SO4, for GCSE the teachers don't like to use it because it doesn't contain all the procedures that the examiner will be looking for. I can often persuade them to use it for year 7 or 8
 
If this is the method using 1.4M H2SO4, for GCSE the teachers don't like to use it because it doesn't contain all the procedures that the examiner will be looking for. I can often persuade them to use it for year 7 or 8
Yes that is the one. A shame - there is much less waste.


What part of the procedure does it not include?
It involves heating the acid, adding xs, filtering, evaporation, crystallisation.
 
The only one I can think of is the slower evaporation over boiling water. But usually I think it has more to do with how much of the lesson it uses. If the practical is easier and quicker they have to teach more!!
 

CovTech

Lvl 37 Alchemist
COMMITTEE
Yes that is the one. A shame - there is much less waste.


What part of the procedure does it not include?
It involves heating the acid, adding xs, filtering, evaporation, crystallisation.
It's because that method is from April 2016 which makes it older than the new GCSE pracs
 
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