It was the Salters’ Festival of Chemistry at Keele today, organised by Dr Jane Essex from Education. The school children did two lab based activities then were sent to the lecture theatre with me for a chemistry magic show. I did the usual demos (for me) with liquid nitrogen, hydrogen balloons, the blue bottle, the Belousov-Zhabotinsky reaction and elephant’s toothpaste. They are all loosely linked through reactions, visible and audible changes indicating something is happening and gases in air which is OK for the age group (year 7/8 so 12/13 year olds). I’m a bit restricted in the lecture theatre – there used to be a fume hood but alas no more. I’d probably switch out a couple of reactions for some more energetic reactions then.
I try to improve one demo each time I do the lecture. This years ‘innovation’ was to make the elephant’s toothpaste glow in the dark. I usually use 30% hydrogen peroxide (6% does not work very quickly but would be good for students doing the experiment themselves and investigating rates and reactivity), washing up liquid (the foamier the better), and food dye. I’d seen a few videos on the internetz of glowing or chemiluminescent elephants toothpaste (http://www.youtube.com/watch?v=1cDFFJDMCiM) and thought I’d give it a go. I started with fluorescein and tried an ethanolic solution instead of the dye. That didn’t work too well (too dilute) so I switched to higher concentrations and aqueous solutions. Still wasn’t happy with the results so I took a trip to the local photochemist and acquired something that ‘glows brilliantly’ under UV light.
And it did! I made up a water solution of the dye just concentrated enough to be on the point of self-quenching. That way when it was added to the peroxide, the solution didn’t become too dilute in either. I use potassium iodide as the catalyst (2M solution) but other sites use potassium permanganate or dried yeast. I’m not giving quantities because it depends on the reaction vessel. Typically I use 1/10th the volume of peroxide to the volume of container (generally a measuring cylinder), sufficient dye to give good colour, sufficient washing up liquid to give good foam, and sufficient KI solution. You have to test it, and I usually use a measuring cylinder. It took me a couple of hours to get something I was happy with (and fairly confident in).
A photo will follow, but coming home and searching around, I found some information where it could be done using fluorescent highlighter pens (http://www.playathomemomllc.com/2012/03/glowing-reactions.html). What a fantastic idea! And it makes it potentially ‘doable’ in schools. Hydrogen peroxide can be purchased in modest quantities and strengths, yeast and washing up liquid are easy, and highlighter pens is raiding the office supplies. Simple!