Gelli Baff® |

	Gelli Baff®
What’s the mystery?	Sarah and Philip were taking a bath with Gelli Baff, a crystalline powder which is dumped into a bathtub filled with water. The viscous hydrogel was great fun. Now they want to drain the bathtub. How can they force the viscid stuff to go down the plughole?
Domain(s)	Chemistry
Subdomain keywords	Superabsorbents, polymers.
Age group	On a submicroscopic level: 16 to 18 years old.On a phenomenological level: 6 years and older.
Expected time for the mystery	Approximate time for teacher preparation: about 20 min.Approximate time in classroom: two individual 50-min. lessons.
Safety/supervision	The superabsorbent can be used by kids. There are no safety restrictions or regulations except that the substance should not be eaten!Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials	Coloured superabsorbent for the bathtub (e.g. Gelli Baff), nappies, uncoloured superabsorbent polymer, toothpastes, hair gels, crystal sugar, crystal soda, vinegar essence, lemon juice, citric acid, salt, sea salt, powdered sugar, plastic bowls, measuring glass, measuring container, porcelain cup, matches, spoons, stirrers, etc.
Learning objectives	Students will learn about swelling reactions, balanced reactions, and polymerisation.Students should be able to describe how a superabsorbent works and establish a relationship between superabsorbents and polymers. Students should be able to describe how the gel becomes liquid again. Students should realise the relationship between the absorption ability of the absorber and the salt concentration in the liquid.
Resources	A PowerPoint presentation about forest fires, polymers, and the chemistry of nappies written by H. Eck (2011, in German). Experimenting with FAVOR®-Superabsorbents (in German).