Goldenrod Paper Indicator with a Black Twist

Goldenrod-colored paper once came with a pigment formulation that was pH sensitive.  Apparently similar to pigments present in turmeric, these paper pigments were yellow in an acidic environment (like vinegar) and red in a basic environment (like ammonia).  This goldenrod paper was long used as big indicator strips for pH demonstrations, including hidden messages written in wax and developed with ammonia solution and "bloody" handprints made from ammonia solutions.  See http://www.stevespanglerscience.com/lab/experiments/goldenrod-paper-message and http://blog.teachersource.com/2014/10/23/seeking-goldenrod-paper/ for more details. Here is an example of a wax-written message.

The formulation of the paper has changed (apparently the old formulation was not very recyclable) and the dyes are no longer pH sensitive.  Many science demonstration suppliers stockpiled the paper with the old formulation for a time, and there have been some shortages in the past.  There is a way to make a sort of goldenrod paper using turmeric itself, see http://blog.teachersource.com/2014/02/05/make-goldenrod-paper/.   Here is an example of turmeric (an old sample from the collection of the late great Doris Kolb) in various solutions: yellow in vinegar, reddish in ammonia, and dark brown in 6 M hydrochloric acid.

I still possess many sheets of the old goldenrod paper, which I use for demos and will now guard more carefully.  So, what is the black twist?  A couple of days ago, I accidentally put a piece of old goldenrod paper in contact with 6 M hydrochloric acid solution and it turned black!  Unlike with ammonia solution, the color did not readily fade when the solution dried.  Areas of the paper adjacent to the blackened locations also darkened, possibly due to diffusion of HCl vapor. The yellow color can be largely restored by spraying with vinegar or with ammonia solution (it turns red and then fades back to yellow).  I have not been a fan of the "bloody handprint" demo, at least the "bloody" analogy, so we have often attached pipe cleaner "legs" to turn a handprint into a hand turkey.  The ability to make the paper black will now allow me to use hydrochloric acid to draw the legs, an extension of the indicator theme. Here is a test run: first, an ammonia handprint with some hydrochloric acid highlights; second, the ammonia leaves after a time and the black features become more diffuse; and third, after spraying the left leg with vinegar and the right leg with ammonia solution and waiting, colors have somewhat returned to yellow.

Liquid nitrogen as a herbicide?

I had some extra liquid nitrogen, so I poured it on a patch of weeds in the yard.  Two days later it looked like this (the brown patch at the right side of the picture).

Growing Bismuth Crystals and Bismuth Oxide Films

Some students asked if they could try growing hopper crystals of bismuth from molten bismuth, so I tried it first by myself today.  It was conceptually simple to do (melt bismuth in a ceramic crucible and carefully pick crystals out from under the cooling surface layer), but I think to do it well (like much other crystal growing work) requires a bit of practice and maybe even artistry.  What I also thought was fun was watching the hot liquid bismuth oxidize in contact with the air.  When the skin of oxide was pushed away from the liquid bismuth, the freshly exposed liquid surface turned from silvery to yellow to red to blue as the oxide layer thickens (see pictures below).  This reminds me of a paper I was involved with a few years ago - see: D. J. Campbell, M. S. Baliss, J. J. Hinman, J. W. Ziegenhorn, M. J. Andrews, K. J. Stevenson, “Simple Methods for Production of Nanoscale Metal Oxide Films from Household Sources” J. Chem. Educ., 2013, 90, 629-632.  It would be interesting to calculate and directly measure the visible spectrum of that oxide layer and connect it to the layer thickness.

20th Anniversary of the Oklahoma City Bombing

Ammonium nitrate finds its way into any good discussion of nitrogen chemistry.  This compound, used as a fertilizer in many cases, also can be used as an explosive.  A former student of mine had a parent that worked at a company that mixed ammonium nitrate and oil to produce a blasting material for construction purposes. The oil adds more reducing power to the redox reactions involved in the explosions, increasing their potency. Unfortunately, many terrorists have produced a similar mixture and used it in events such as the Alfred P. Murrah federal building bombing in Oklahoma City in 1995.  Accidents involving ammonium nitrate also occur, including the Texas City disaster in 1947 (a blog entry from April 20, 2013, discusses that). In 2010, I visited the Oklahoma City bombing memorial, so I am posting pictures of that visit here.