Temperature can help determine how fast a substance dissolves. To test how temperature affects a solute, provide two clear cups and a timer for each student. Place a sugar cube in each cup. Pour cold water into one of the cups. Have each student stir the water with a spoon or coffee stirrer while timing how long it takes for the sugar cube to dissolve. Have each student record the result. Repeat the process with the hot water. Hot water experiments are safer to conduct in the upper elementary grades than lower grades. (You do not need to use boiling water.) Discuss the time differences between the two temperatures and how they affected the sugar cubes. Cold water dissolves less of the sugar and dissolves it more slowly than hot water.
Solutes that look similar can be deceiving. Give each student three clear cups. Provide a tablespoon of sugar, salt and sand to each student. Have each student work with one substance at a time and sprinkle it into a cup of water. Record the results of which solutes dissolve and which substances float or sink to the bottom of the cup. According to Lesson Planet website, when too much of a substance, such as salt, is used in a solution, such as salt in water, the solution becomes saturated and the salt will accumulate on the bottom of the cup, taking longer to dissolve.
Use cold and hot water in different containers and experiment with powders such as stirrer, baking soda, flour, baking powder, powdered sugar, powdered laundry starch, powdered laundry detergent and sand. Record the time it takes (if any) for a substance to dissolve in hot or cold water. Discuss the time differences and which substance failed to dissolve.
Candy experiments may require special permission if your district has a no candy policy. Give each student a chocolate square or chocolate chip, a piece of crystal sugar candy and a sweet-and-sour candy tart. Each student should also have a timer. Record the amount of time required to dissolve each candy in each student's mouth without chewing or sucking. The candy should sit on the tongue within a closed mouth.