Summary Make a foam as hydrogen peroxide rapidly splits into oxygen and water. Science content Chemistry: States of Matter, Properties of Materials (K-7) Chemistry: Atoms, Molecules (3-7) Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6) Chemistry: Chemical Changes (2, 7) Lessons activity is in Making gases Foams Mixtures showing physical and/or chemical changes Chemical reactions Materials hydrogen peroxide, either bottles available in a drug store (3%), or as oxygen bleach (chlorine free bleach) dish soap dried yeast empty water bottle tray to contain mess Procedure Add about a cup of hydrogen peroxide to the empty water bottle. Add a squirt of dish soap. Add a tablespoon of dried yeast. Swirl to shake, then set the bottle upright on the ground outside, or on on a tray if indoors (it will be messy). The bottle gets warm as the chemical reaction makes heat ("exothermic"). Energy transformation: chemical energy to heat energy. The hydrogen peroxide is split into oxygen and water, catalysed by the yeast: 2H2O2 -> O2 + 2H2O. The oxygen gas makes tiny bubbles. Molecule models can be used to show this chemical reaction. The dish soap stabilizes the bubbles to make a foam - one end of the detergent molecule does not like water ("hydrophobic") so it inserts into the gas bubbles; the other end likes water ("hydrophilic") so sticks outside the bubbles into the surrounding water. The soap molecules surround the oxygen gas bubbles in this way and stablize them so that they last for a longer time - as a "foam". As the oxygen is continually made the foam squeezes out of the bottle like toothpaste...for an elephant! Foam is a kind of a mixture called a colloid - gas bubbles in a liquid. See attached file for other colloids. Science centre demonstration using a higher concentration of hydrogen peroxide: https://www.youtube.com/watch?v=ei5kGOW1wT8 Attached documents mixtures_summary.pdf Grades taught Gr K Gr 1 Gr 2 Gr 3 Gr 4 Gr 5 Gr 7
