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Copper and acetone part II

OK so I hope you enjoyed the movie with the copper “cat” dancing in and out of the jar with the acetone. Now it is time to look at how it was done. While I accept no responsibility for whatever you might do (please see the disclaimer in the post with the video) here is the equipment which I used to do the experiment. 

Equipment used for the acetone and copper wire experiment


Note that I keep a fire blanket close by when I am doing any experiment which involves fire or flammable liquid, also off screen we have the copper wire. Also do note that when working I avoid wearing anything other than cotton (or polyester cotton). Nylon clothing does some very nasty things in a fire which can make an injury much worse so I normally avoid wearing most man made fibers while doing chemistry. 

We have a large glass jar, a butane torch, some acetone and a lighter. The first thing I did was to place a little acetone in the bottom of the jar. If you put the lid on and shake the jar the acetone fumes quickly fill the jar. The next thing to do is to put the acetone away in a safe place very distant from where you will work. I will not give the full experimental details here of how to do the experiment here. 

Firstly look at the copper wire which has been used several times in the experiment, you will see how it has a dark coloured coating. 

Used copper wire


This dark colour is due to the copper oxide layer on the copper metal. We need to consider what it will look like on the microscopic scale. Copper is a cubic solid, here is a picture of the unit cell. The unit cell can be thought of as a repeating brick which exists again and again in the solid. 

Unit cell of copper


We can cut this cubic solid in three basic ways to get different surfaces. The most simple one is Cu 100, below I am showing several views of this surface. You will see a square arrangement of copper atoms. 




Next we will cut our cubic solid to get the 110 surface, again for your enjoyment I have included a series of different views of this solid. What you should look for is that the copper atoms are now arranged in rectangles. In the gaps between the raised lines you will see a line deeper inside the solid. 






Now we have the last surface for today, which is the Cu111 surface. The important thing about this surface is that the atoms are arranged in a hexagonal manner. 





If we consider the active surface then the following occurs, when the hot copper is able to react with oxygen gas then firstly an oxygen molecule hits the surface and then sticks to it using a simple physical attraction. This does not mean a romantic attachment it is just the case that the oxygen is attached to the surface by weak physical forces. 

What happens next is that the oxygen molecule is broken into two atoms which then form chemical bonds to the copper atoms in the surface. This is a strong bonding which holds the oxygen onto the surface. Using a method called “Low Energy Electron Diffraction” (LEED) it is possible to find where the oxygen atoms are on the copper surface. The Cu110 surface is known to bind oxygen, if you want to see how then I would suggest that you go and read W. Liu et. al., Surface Science, 1995, volume 339, page 151 onwards to 158. 

In short they imaged the way in which the oxygen bonds to the surface. What happens next is that the fuel bind to the surface and a reaction at the surface occurs. The reaction only occurs at the surface and not in the bulk of the mixture (gas phase) 

To prove that the fuel reacts with oxygen at the surface, I took hot copper and I exposed it to acetone in a bottle whose shape was such (wine bottle) that very little oxygen could diffuse in. The reaction was allowed to slowly run out of oxygen. When the copper was cold I pulled it out of the bottle and it was now longer dark. It was now free of almost all of the oxide layer now. Below is a photo of the reduced copper. 

Copper reduced using acetone vapour


 Bye for now, if I feel super keen I will draw the Cu110 solid with the oxygen atoms present on it.


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