Summary Make a swirl of colour patterns, formed as the mixture of molecules in milk are reorganized by soap. 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) Science competencies (+ questioning + manipulation + others that are in every activity) Questioning/predicting: predicting (1 up), hypothesizing (7) Processing/analyzing: comparing observations with predictions (1 up) Materials large plate, any colour full fat milk, half cup or a little more, to reach the edges of the plate food dye colours in dropper bottles Q-tip dish soap Procedure Pour the half cup of milk onto the plate, or until it fills the plate. Add drips of food dye into the centre of the milk. Dip the Q-tip in the dish soap, to soak it up. Dip the Q-tip into the food dye colours. The colours will scoot away from the soap. If you hold it in place, the dish soap will keep coming out of the Q-tip and the colours will spread further and further. Try touching the milk in several places. What's happening? The chemistry is complex. Simple explanation: Milk is a mixture of a fatty part and a watery part. The food dye stays in the watery part of the milk. Soap likes to attach to both fatty and watery things, so as it spreads out it makes the different parts of the milk swirl around. The food dye in the watery part is swirled around too, making the patterns. More complex explanation: The fat in the milk is in tiny droplets, separate from the watery part of the milk. (Milk is a type of colloid called an emulsion. The fat droplets can be seen under a microscope.) The food dye stays in the watery part of the milk, separate from the fat. The dish soap has molecules with two parts - one part likes to touch fat molecules, and the other part likes to touch water. At first the soap spreads out as it attaches to water molecules, pushing the food dye aside. The soap also attaches its fat-loving part to the milk fat, which causes more movement that pushes the food dye around. As different parts of the soap molecules attach to the fatty and watery parts of the milk, the food dye is moved around, making swirling colours. See explanation at https://www.acs.org/education/whatischemistry/adventures-in-chemistry/e… Notes Try with low and non-fat milk, and higher fat cream, to see the difference.
