Mel Science . Chemistry – Egyptian Night

This next Mel Science . Chemistry kit explores two reactions, igniting iron powder over an open flame and an experiment called “Egyptian nights” which explores the role of iodine interactions with starch.

In the first experiment, fine iron powder is scattered over an open flame. The resulting pyrokinetic show fascinating to watch. If I captured the video in slow motion, I would be interested to know at which sizes of powder particles certain kinetic behavior is observed (such as shooting star motion at 1:00, parabolic motion of spark around 1:02, or mini-fireworks at about 1:51!)

Scroll to about 1:00 to see some iron powder spark shooting star and parabolic motion and 1:50 for mini-fireworks display. 2:44 provides contrast of light in a darker setting on white background.

The second experiment included in this kit examines some chemistry that is part of our diet. Starch can be found in all sorts of places and is a needed nutrient in our human diet (probably important for other organisms too!). This experiment requested using potato starch, although corn, rice, bean and other starches could be used — generally starches have the molecular formula (C6H10O5)n . H2O. The starch is mixed into solution containing water, followed by Na2S2O3, KI, NaHSO4 and H2O2 with end result that the starch solution turns dark, reminiscent of starless dark nights (why Egyptian is added as a descriptive I don’t really fathom). Adding additional Na2S2O3 into this mixture results in the darkness clearing up so that the solution returns to a transparent color.

The stark difference in opacity (clear or dark) is a result of the chemistry of iodine, in the form of I- and I2 (and I3-) that reacts with the starch (containing amylose [1] and amylopectin [2], for example). Thus, any starch containing solution should be expected to turn the dark (blue or purple) color. The other compounds also have important function: sodium hydrogen sulfate releases protons (hydration component in water solution), KI gives the ions potassium and iodine, H2O2 is an oxidizer, and the sodium thiosulfate reacts with iodine (2Na2S2O3 + I2 –> Na2S4O6 + 2NaI.) This latter compound is added in solution to hinder the iodine from meeting up with starch (and that is what changes the color back to transparent).