Summary Using a transmission microscope, watch molecules bump into tiny fat droplets in milk, to observe the motion of molecules. 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) Evaluating: inferring (3 up) Lessons activity is in Mixtures with a focus on colloids Properties of materials: sticky, stretchy, floating, long and strong Materials transmission microscope to view at 100X and 400X slides and coverslips 2% milk Procedure Make a slide with a drop of 2% milk, and place under the microscope. Wait until the milk has stopped streaming around the slide, and the individual fat droplets in the milk stay within the field of view. Look closely for the fat droplets jiggling around - caused by water molecules bumping into them! Brownian motion was the first convincing evidence that atoms and molecules existed. (Milk is an emulsion, a type of colloid - tiny fat droplets held in the watery parts of milk. The fat droplets are all small enough to stay in the milk, and not settle out as a separate layer.) Grades taught Gr 1 Gr 2 Gr 3 Gr 4 Gr 5 Gr 6 Gr 7
