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Name: Andrew Status: student Grade: 9-12 Location: DE Country: USA Date: Spring 2012

Question:
Recently I did an experiment just to try it out. I mixed a ribbon of magnesium with white distilled vinegar and it turned a deep crimson after a few weeks. I never knew that it would do this, but I tried to add onto this by seeing if calcium carbonate (drawing chalk?) would affect the acidity or cause a reaction. I used a pen to stir it because it was the only thing I had to use, but I have noticed now after about two days, the pen is releasing a green cloud whenever I open it. The pen is a Zebra click pen and whenever I click it, a cloud of green dust or substance comes out. What is it? Why is the pen doing this? Was it caused by using it to mix the items in my experiment?

Replies:
I am not sure I can make a total sense of your experiences, Andrew. Your story runs on a long distance with relatively few controlling details of the sort scientists often use. But some things come to mind, so I will mention them.

Magnesium tends to be colorless as oxides or ions in water solution. It reacts with acids much faster than weeks, more like minutes. So your few weeks implies two things: - there was definitely insufficient acid to finish the reaction promptly - there may have been some way the mix could pick up contaminating other metals, particularly if the container exposed any metal.

Since the acid was depleted, there were mostly only salts in a near-neutral solution. I would not see any point to adding carbonate to neutralize it. But no big deal.

I have some stick pens (not click pens), and I remember that the tip has a cone of yellow metal, presumably brass. Brass is copper plus some zinc plus maybe a little of other things. Many copper salts are pale blue-greenish and easily powdered. Copper carbonate or acetate or a mixture sound likely. The presence of those ions could have de-stabilized the normal passivating oxide of the brass (which would be zinc oxide I think), catalyzing the brass's corrosion in oxygen and water vapor.

Back to the magnesium and crimson. Metal that is finely divided but not yet oxidized usually takes on some dark color: black, or black-with-a-tint, such as dark brown or dark purple. So with magnesium ribbon (highly wanting to be oxidized) sitting in a water and salt solution ( which could mess up the clear or whitish MgO which normally forms), it is possible that some different smothering layer formed on the surface, slowly letting some oxygen and/or water in for further corrosion reaction, but not letting enough in to oxidize all the Magnesium metal. White salts and oxides mixed with nano-scale bits of unoxided metal mixed in could be purplish or reddish. But I really cannot know. If that is the case, I think it should be quite dissolved to clear watery solution by adding more acid, strong acid, preferably hydrochloric acid. If the color was from some contamination, then maybe it would be reluctant to disappear completely, These two cases can be more difficult to distinguish between than it sounds. Heating the colored mix in a ceramic crucible over a Bunsen burner would probably tend to complete the oxidation of magnesium too. I would prefer you did that with supervision, until you are experienced. Inorganic analysis is a game that used to be played a lot in high-school chemistry. I wonder if information on that can be found on the web.

You might surf the web for what glassblowers or ceramics artists use to color glass and ceramics red. Copper comes to mind. but it depends a lot on the degree oxidation of the solid oxide mixture. Palladium makes wonderful deep red solution in water. It is an expensive metal, though, half the price of gold or platinum. Chromium impurity will dope clear aluminum oxide to red color, also known as ruby. You can get some chromium from stainless steel or some aluminums. Notice my uncertainty over whether your crimson is in water-solution or a solid solution in an oxide. The same metal ion can make different colors depending on what it is dissolved in.

Jim Swenson


You have to be careful about using inks from ball point pens – especially “black” inks. Very often the inks are not actually purely “black”. They are formulated with dyes of several colors. The purpose is to keep the formulation black. The addition of CaCO3 will change the pH of the ink which in turn can alter the color of the ink. In many cases CaCO3 is present in the paper formulation. This can cause a change in the pH, which in turn will change the color of one or more of the dye components of the ink.

Vince Calder


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