The chameleon bubbles |

	The chameleon bubbles
What’s the mystery?	Chameleon bubbles are alginate bubbles that emerge when a sodium alginate solution is dropped into a calcium chloride solution – just like how bubbles in bubble tea are made.The bubbles can change their colour with respect to the substance with which they are filled. In this case, the bubbles are filled by an acid-base indicator solution; so, adding acids or bases in the outer surrounding leads to colour changes inside the bubbles by diffusion and pH change – just like how a chameleon can change its colour. Since acids and bases are colourless liquids, adding them to the solution around the bubbles leads to mysterious colour changes.
Domain(s)	Chemistry
Subdomain keywords	Sodium alginates, acids, bases, indicators, semi-permeable membrane.
Age group	14 to 15 years old.
Expected time for the mystery	Approximate time for teacher preparation: 15 min.Approximate time in classroom: 90-min lesson.
Safety/supervision	Students should wear safety goggles and lab coats. Acids and bases are corrosive.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	Sodium alginate, calcium chloride, diluted hydrochloric acid, diluted sodium hydroxide solution, salad herbs, vinegar, vegetable oil, red cabbage indicator, other indicators.
Learning objectives	Students can learn about acids, bases, indicators, neutralisation, and diffusion through semi-permeable membranes.
Resources	Brandl, H. (1998). Trickkiste Chemie. Bayerischer Schulbuch Verlag, München.