Two months ago, when I was helping my brother clean his room, I found a book with experiments for kids. I expected things like “what happens if you put salt in water”, and while those were definitely included, there was one experiment that grabbed my attention. It claimed that if you put copper wire in vinegar, the solution will become blue.
How the reaction works
After some research, I discovered this reaction was a redox reaction with the copper wire as a reducer and the acid in vinegar as an oxidizer. Calculating the difference between the standard electron potential of the oxidizer and the standard electron potential of the reducer gives a negative difference smaller than 0,3. This means the reactions isn’t likely to happen without adding a stronger oxidizer such as hydrogen peroxide. In fact, this reaction will take place, but this will take a long time, without the hydrogen peroxide. Adding this is necessary to speed up the process, but with a lot of patience it should be possible to do this experiment without it. I thought it would be fun to test this and this is where my project started.
Starting my experiment
I decided to start on a small scale since I wasn’t sure if it would work. I took a few pieces of copper wire and a small amount of vinegar and I left it in a beaker. After a few days the solution had a slightly blue colour, but unfortunately it wasn’t nearly as blue as the picture in the book.
The process turned out to be even slower than expected, so those few days were not enough to complete the reaction. I figured the cause was the vinegar I used. Vinegar is a solution of acetic acid in water. This acetic acid only reacts with the copper when the concentration is high enough. The vinegar I used was a 7% solution and was way too diluted and therefore too weak to react with the copper. Fixing this was not a big problem. All it took was to leave the beaker (with vinegar) and the copper wire a few days outside when it was warm and sunny. The water slowly evaporated and while the concentration of acetic acid became higher, the colour became darker. This darker blue colour showed that the solution was now strong enough to react with the copper wire.
Once it looked like the reaction was finished, I took out the remaining pieces of copper wire and put the beaker with the bright blue solution on a hot plate. The water evaporated and a dark green solid stayed behind in the glass. This was the desired copper(II)acetate.
Accidently making basic copper carbonate
The evaporation was only used to see if it was possible to create solid copper(II)acetate, but since I wanted to make some other precipitates, I dissolved everything again using water. I was trying to make copper chloride by mixing some sodium chloride solution with the copper(II)acetate solution, but stupid as I was, I forgot the difference between Cu+ and Cu2+ -ions. Cu+ -ions will precipitate with the chloride ions and make the insoluble copper(I)chloride. Cu2+ -ions will form the in-water-soluble copper(II)chloride, which of course won’t precipitate. Since my copper(II)acetate solution only contained Cu2+-ions it wasn’t possible to create the precipitate with chloride ions. So, I was left with a green/blue solution, but at this point I wasn’t aware of my fault yet.
I decided to do another evaporation, just to see what would happen. It took a long time to do this because the volume of the solution had increased a lot due to the adding of sodium chloride solution, but after a while I saw some solids starting to form. The solids were arranged in a strange pattern and at one point it even looked like there where crystals growing in the beaker. The colour slowly turned form blue/green to light green during the evaporation. Both observations made clear there was another product but copper(II)acetate. I had literally no idea what this could be, but I liked it.
A few days of research went by. I searched for pictures of all the possible salts with the ions I had, but none of them had a colour that looked like my product. After a while I realised that I had been using tap water both to dissolve the copper(II)acetate, and to make the sodium chloride solution. I knew tap water contained chalk, but I never realised it was enough to majorly affect a simple experiment like this. After including Ca2+ and CO3 2- -ions in my research, I figured that my product looked the most like basic copper carbonate, also known as copper(II)carbonate hydroxide. I was happy that I finally discovered my unknown creation, but I didn’t know what to do with it, and I still don’t. The colour looks nice so for now I decided to keep it in a glass container. Maybe I can do something with it in the future.
Making copper(II)acetate again
Because I (accidentally) made basic copper carbonate, I had no copper(II)acetate anymore. I decided to make it again, this time on a larger scale, since it turned out to work well. I started with 20 grams of copper wire and 50 millilitres of vinegar. Whenever there was almost no vinegar left due to evaporation, I filled it again. After three weeks the solution had become vibrant blue, but unfortunately, there were also some impurities. The beaker had stood outside and uncovered the whole time, which meant some sand and little flies had found their way in. To fix this, I decided to build a gravity filtration set up.
For the gravity filtrations set up I used a funnel, a coffee filter, and a beaker. I poured everything in the filter, including all the pieces of copper wire and washed it a few times with distilled water. After the filtration was done, I was left with a clean solution and had gotten rid of all the copper wire. I’ve filmed the whole filtration process and turned it into a time lapse, which can be seen on my Instagram page.
I left the clean solution outside in the sun for another week so all the water could evaporate. In the meantime, I found a way to build a simple vacuum filter. I thought it would be nice to use this for the next filtration, since the gravity filtration process was quite slow. I used the vacuum filter to get rid of some new impurities after the evaporation.
Originally, I planned to speed up the evaporation process by filtering the suspension that had formed during the evaporation, but the solid particles where so small, they all passed through the filter. Although this small failure was a bit disappointing, I was still happy with my self-build filter as it definitely accelerated the filtration. If I manage to do a filtration that actually works, I’ll share it. For now, I think it isn’t interesting enough to share it yet.
Now that my solution was free of impurities again, I had two choices. I could use a hot plate to evaporate all the water and dry out the solid copper(II)acetate, or I could take some time to wait for the warmth outside to do its work. I decided to go for the last option since using the hot plate wasn’t very safe. Luckily enough the weather was nice, so it only took one week for the copper(II)acetate to dry completely. Once this was done, there was just one chunk of copper(II)acetate, which was so weak it broke when I tried to get it out of the beaker. I decided to crush it all into little pieces and discovered the inside of the big chunk wasn’t completely dry yet. For this reason, I left all the little crystals a few more days in the sun in a petri dish.
After those few days, my copper(II)acetate was finally done! The crystals where small but looked awesome. When I used a computer microscope to have a better look on those crystals, I discovered that the crystals where shaped quite interesting when there was still some suspension around it. The dry crystals also looked insane in my opinion.
You can see the pictures I made below this text.
I think using the computer microscope and making pictures with it is such a cool addition to my experiments since it makes it possible to have a better view on the results. I think I’ll do this more often!
Looking back at this project, I had a lot of fun with it. I still don’t know what to do with the basic copper carbonate and the copper(II)acetate, so I’ll store it somewhere and maybe I can do something with it in the future. For now, the most important thing is the fun I’ve had and the new things I learned!
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