Beilstein Test with Christmas Lights

I have heard over the years about placing old Christmas lights into a campfire to make the flames turn green. This is a variation of the old Beilstein test for halogenated compounds, where copper metal reacts with halogens in a flame to turn the flame green.  In the case of the Christmas lights, the halogens are supplied by the chlorine in the polyvinyl chloride (PVC) insulation and the copper metal is supplied by the electrical wiring.  I tried this with a little bit of Christmas light wiring and the flame from a propane torch.  When the copper wire alone or PVC insulation alone was in the flame there was no green color, but where there was exposed wire near the insulation the flame turned green.

Decomposition of Esters in Old Scented Markers

We have some old scented markers in our Sunday school classroom and I have noticed that in addition to the pleasant fruity and minty smells I noticed that there is a sort of a vinegary smell.  I assume that is due to the esters that produce the scent decomposing to produce carboxylic acids such as acetic acid.  Our department chair has pointed out to me that when he opens a bottle of uncoated aspirin he can briefly smell acetic acid, presumably from decomposition of that ester.

Flashbulbs

Wow, I guess it has been a while since I have added to this blog.  Recently, I found several unused flashbulbs produced by General Electric.  Each bulb contains very fine wire which resistively heats and burns in the oxygen atmosphere of the bulb, producing a bright flash.  Felicia Staiger acquired a scanning electron microscope image and an energy-dispersive X-ray spectrum of the wires.  The spectrum indicated that the wires were comprised of aluminum.

 

Chrome-plating

In my General Chemistry II and my Engineering Chemistry courses, I compare the corrosion behavior of iron and chromium, and mention how the very thin layer of oxide that rapidly forms on a layer of chromium metal helps prevent further corrosion of the chromium layer and the iron that typically supports that chromium layer.  This old car that I saw today, with its rusty iron body and its shiny chrome highlights, might be an illustration of these ideas.

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.

Shrinky Dink® Stuffed Animal Goggles

I have previously blogged (see: http://campbelldemo.blogspot.com/2012/05/homemade-shrinky-dinks.html) about how transparent polystyrene packaging such as those used to hold baked goods can be used to make plastic trinkets, and how this polymer behavior is the basis for Shrinky Dinks®, a craft/toy that was popular in the 1970s and 1980s, and can still be purchased today (®Shrinky Dinks is the Registered Trademark of K & B Innovations, Inc.).  I have found that if you trace a pair of lab goggles onto a sufficiently large piece of polystyrene packaging, cut it out, punch a hole at either side, and shrink it in a toaster oven, the resulting goggle shape is a size that fits stuffed animals. I used an elastic band to hold the "goggles" in place.

Human Battery

In my electrochemistry lectures I point out that a person's fingers can be a salt bridge in an electrochemical cell.  In an energy exhibit at the St. Louis Science Center yesterday I saw a great demonstration of a person being an integral part of a battery.  There were two pairs of metal plates (each pair had a copper and a zinc plate connected by a wire) connected to a sensitive voltmeter.  When my hands were  placed on plates of the same metals (Cu and Cu or Zn and Zn), no electrochemical potential was established and the voltmeter read zero.  When my hands were placed on a Cu and a Zn plate that were electrically connected away from the voltmeter, the voltmeter read zero.  When my hands were placed on a Cu and a Zn plate that were electrically connected through the voltmeter, the voltmeter needle deflected as oxidation took place at the Zn plate and reduction took place at the Cu plate.  The direction of the needle deflection depended on which specific plates were touched. The magnitude of the deflection seemed to vary with the quality of the contact made with the plate (illustrating the significance of resistance in the cell).  I was reminded of a "potato clock" only this time it was a couch potato involved in the battery!  Another nice exhibit located nearby had a rod that one could gently displace to demonstrate the magnitude of a joule of energy.

pH Sensitivity of Purple Grape Juice

I have blogged before about grape juice as a dye (see: http://campbelldemo.blogspot.com/2012/05/grape-juice-prints-on-clothes.html), blackberry juice as a dye (http://campbelldemo.blogspot.com/2012/05/dyeing-seashells-with-blackberry-juice.html) and pigments in plants being sensitive to pH (http://campbelldemo.blogspot.com/2012/05/ph-sensitivity-of-colorants-in-flower.html).

So, I think it is time to mention an effect that I have been noticing for years but saw spectacularly this morning.  Purple grape juice is red out of the bottle (or out of a frozen concentrate can), but when the juice is diluted the color shifts to blue.  I interpret this as the anthocyanin pigments changing color when the pH of the solution increases as tap water is added to the juice.  The picture shows the reddish undiluted grape juice at the left, and grape juice blue as it is diluted into water at the right.

Visit to J Draper Glass

There is lots of fascinating chemistry associated with glass (my Bradley University colleagues Ken and Doris Kolb have presented and written extensively on the subject), and to appreciate glass properties one really needs to work with hot glass.  Yesterday, students from the Bradley University Chemistry Club visited the J Draper Glass studio to see a glassblowing demonstration and to participate in making their own glass paperweights. Jeremie Draper (in the gray and orange shirt) and her assistant Misty Long did an excellent job explaining the art and science of working with the glass.