Instruct the students to sit in a circle. Introduce the unit by presenting a glass of water, small rocks and sugar cubes. Ask the students what they think will happen when you drop the rocks and sugar cubes into the water. After you place the items in the water, introduce the word “dissolve” as the reason the sugar cubes disappear and the rocks don’t. Ask students what they think will happen if you stir or heat the cubes. Following a demonstration, discuss why those processes dissolved the cubes faster.
Even though it is the messiest part of the lesson, students need hands-on experiences. Have the children visit a science center -- with adult supervision -- in small groups. Provide spoons, glasses of water and items such as sugar, tea, sand, coffee, flour and salt. Include pictures of each item that can be attached to a chart. Create a poster board divided into top and bottom sections -- one for predictions and one for experiments. Write the headings “yes” and “no” at the top of each section. Record students’ predictions of whether the items will dissolve in water. Students then drop the items into the water glasses to determine if their predictions were correct.
Provide a small bag of packing peanuts for each student. Make sure they’re made of cornstarch, not foam. Ask students if they think the peanuts will dissolve in water. Conduct a demonstration to show that they dissolve. Instruct students to use their imaginations to create something -- an animal, a person, a house -- with the packing peanuts. Give each student a wet sponge or paper towel to moisten the peanuts so they’ll stick together. Caution students not to get the peanuts too wet -- they will dissolve. Send the projects home on a dry day and tell students to explain dissolving to their families.
Make signs containing the word “water” and other words to represent substances that will or will not dissolve in water, such as “rock,” “salt” and “sugar.” Hang them around the students’ necks. Students form a circle to prepare for role-play. Those who are wearing the “water” signs begin moving around inside the circle. As you call out the names of other substances, students mingle with the water if they represent substances that dissolve in water, or fall down if they represent items like rocks that don’t dissolve. Each time a different substance is introduced, stop and discuss what happened.