STC Program: Changes, 2nd Edition
Initial activities in the unit expand students' understanding of solids, liquids, and gases by exploring changes in state. Students consider the changes to a single substance-water-as they observe it freeze, melt, evaporate, and condense. Then, through a sequence of lessons, they investigate changes involving mixtures. Student pairs produce mixtures of 2 solids and of solids with liquids and they observe and compare the changes that result. They also set up "dissolving races" with sugar and water.