After a while of not posting, here’s a simple prep that I managed to screw up twice.
At first I have attempted to replicate a synthesis found on sciencemadness.org, as it seemed simple enough. 2.49 grams of copper (II) sulfate were added to 60 degree C water and stirred until dissolved. After, 3.68 grams of potassium oxalate monohydrate were added to the solution, and a murky cloud of copper (II) oxalate were formed. At that point, I was screwed. Some of the complex has formed, indicated by a darker colour solution, but a mass of insoluble copper oxalate settled on the bottom. It didn’t seem eager to redissolve.
On my second attempt, I dissolved the same amounts of chemicals in two different solutions, and added the hot CuSO4 solution to the hot oxalate solution. At first it went well, once again complex formation was visible by the changing colour of the solution, but when adding the last portions of copper, the same disgusting pale-blue copper oxalate precipitate made its unwelcome return. At which point, I was screwed again.
As I deduced, the issue was in the wrong stoichiometry provided in the original post. Looking at lab protocols for the same complex, all of them used an excess of the oxalate, which I didn’t.
Successful Attempt:
2.00 grams of copper (II) sulfate pentahydrate were weighed out and dissolved in 30 ml of dH2O in a small beaker. 6.20 grams of potassium oxalate monohydrate were also weighted, and dissolved in 40 ml of dH2O in an erlenmeyer flask. Both solutions were heated below boiling until both solids were completely dissolved, and the copper sulfate solution was slowly added to the oxalate solution with strong stirring to prevent copper oxalate precipitation. The liquid was left standing on the hotplate for 5 minutes and then was placed in an ice water bath to precipitate the product (needle shaped crystals) out.
The final yield was 2.35 grams (74%)
