Identifying Techniques for Filtering/Purifying Aqueous Copper Sulfate

 

Small Scale

I took an unknown amount of copper sulfate crystals and threw them into a clay pot from Pottery Barn. I siphoned off the water with a turkey baster and put it into a dedicated glass container, which I then transferred to a 2L erlenmeyer flask, covered it with cheesecloth, and gently set it on top of my radiator to evaporate. Once crystals started forming, but before everything evaporated, I put the flask in a garage which was pretty much around 32 degrees fahrenheit for 2 weeks. The crystals grew fairly large, and then I put it back on the radiator for about a week.

 

I saw that crystallization was a success so I started a larger scale batch. But I would go back to this first experiment and make some changes afterward, as the story will tell.

Large Scale

I had about 5 pounds of copper sulfate which I dissolved in distilled water, purchased from a local supermarket. 5 pounds gave me more than 5 gallons of aqueous material, which I put into a plastic/polyurethane paint pellet I got from a hardware store. I stretched some cheesecloth over the top to prevent lint and dust from settling in.

 

I originally dissolved the copper sulfate in water in a piece of cylindrical glass I got from a local furniture store, and I would siphon out whatever was tinged with a turkey baster. I only filtered the aqueous copper sulfate with the mesh cheesecloth. Some days later, I was observing the batch in the second photograph and was curious why the larger crystals were deep blue and why the smaller crystals on the bottom were yellowish-green.

 

 

Some days later I came to the conclusion that when aqueous copper sulfate is allowed to settle, it starts to precipitate or accumulate a layer of yellowish, spongey matter. I took the above and below pictures last night to illustrate the phenomenon; this particular batch had been sitting for weeks.

 

When jostled and swirled around, this material becomes so dissolved and scattered through the liquid that it becomes hard to detect and very hard to filter unless done through a thick object, like a piece of cloth. Cheesecloth, I discovered, only filtered out impurities that were thick enough to get caught in the mesh, which I thought were the only real impurities worth getting rid of. But after realizing that this pongey substance formed in several batches of my solutions, it must be a thing common to all kinds of aqueous copper sulfates when they are made from industrialized laboratories. Perhaps it is a phenomenon common to all dissolved sulfate minerals, but because I am unfamiliar with mining operations in my area and because I haven't found a means of getting raw, natural, "organic" copper sulfate (that's a joke), I will stick with the modern synthesized stuff. So I endeavored to purify my copper sulfate of this material using coffee filters, which worked pretty well. Of course, when I went to buy filters, I was curious about the option of using filters that were 4x as expensive but were apparently made with raw materials and were "chlorine-free" and such. It made me wonder about the use of modern industrial-grade materials in our works and how complex substances with unknown origin might subtle impact experimental results. Ancient chemists hardly had such substances like complex plastics and synthesized fibers.

 

I'm currently doing another small batch recrystallization just to make sure that the filtering with coffee filters is a usable technique. This is a small, maybe .75 liter glass container with a solution of coffee filter-purified copper sulfate which has been evaporating gently for several days. Soon I will put it in the refrigerator so it can sprout crystals, and then I will finish evaporation. Then I can proceed with doing the same filtering process with the 5 gallon paint pellet.

UPDATE: For more information, check out the new notes I've published on the MineralstoMedicines website. They refer to copper sulfate, which I call "blue salt-glass," and also the colors produced when the impurities settle.

UPDATE 2: For those who aren't aware, the first phase of this experiment involves making an acid through a distillation process familiar to ancient chemists: the distillation of vitriols with other materials to produce "strong waters," also known as acids. The first step of that process requires that I have some good-quality vitriol, which is the reason why I'm purifying my sulfates.