I recently started a food science club at school with a fellow teacher. It's a good way for me to try out new stuff with a small group of students, that I eventually want to incorporate into my classes. It's like a real life R and D department. I recently posted about a polymer called sodium alginate. I got a response from Earl Lee on how to make watermelon caviar. So I decided, let's try it out with an after school club. It demonstrates a technique used in molecular gastronomy. A polymer (which is in one of our standards), sodium alginate, is mixed in with watermelon juice. The mixture is then carefully inserted, with a syringe, into a solution of calcium chloride. A chemical reaction happens between the calcium chloride and sodium alginate to form calcium alginate. The calcium alginate is not soluble in water and thus forms a gel around the outside of the watermelon juice. The calcium alginate watermelon spheres are edible. We then experimented with making spheres of cola using the same technique. The students loved the more intense (not to mention the more sweet flavor which their palettes are more geared to) flavor of the cola.
This is another favorite demo of mine. Throughout the years I had mixed results. I finally figured out that Gold Medal all purpose flour works the best with some preparation. I sift a small bag of flour to reduce clumping and ensure the separation of particles. When doing this demo be aware of what kind of fire alarms/detectors are used in the building. In my classroom there is no sensor that will go off. Where I recorded the video, our school's multipurpose room, it (it was about 30 feet above the demo area) could detect the heat/smoke that was released (the alarm sounded about 1 minute after the actual demo).
A polymer, sodium alginate, reacts with calcium chloride to produce calcium alginate. Calcium alginate is a gel that is not soluble in water. A new branch of cooking, called molecular gastronomy, uses this technique to trap flavor sauces in gels to put over food. Not familiar with molecular gastronomy? Lifehacker has a good set of simple videos on the subject. You can order the kit that I used from Educational Innovations.
System A and System B monomers are mixed and polyurethane foam, a polymer, is produced. You can see the dramatic results in a clear cup, or a little more weird, in a latex glove.
This is a different version of the old egg suck into a milk bottle demo. I got this idea from a Steve Spangler demonstration in which he uses a water balloon instead of and egg. Basically a piece of burning paper is placed into a flask and then a water balloon sits on top. The oxygen gets used up during the reaction, creating a lower pressure inside the flask than outside. The balloon gets pushed in as a result.
Thanks to Joshua Buchman for correctly pointing out that I was completely wrong in my explanation. The video now has the correct explanation. The reason the balloon gets pushed into the flask is due to the rapid cooling of the hot gases in the flask once the chemical reaction stops. The gases condense as a result, lowering the pressure inside the flask and the atmospheric pressure pushes the balloon into the flask. I had wrongly assumed what had happened based on the recollections of demos that I had seen in the past.