Help students understand how water creates caves in areas with limestone deposits. Form a limestone cave by stacking several layers of sugar cubes together. Cover the cave with a thin layer of clay. Poke holes in the clay with a sharp instrument, and let the clay dry. Slowly pour water over the top of the mountainlike structure. As the water leaks into the holes, the sugar will begin to dissolve. The result will be cavelike areas.
Give each student a small Styrofoam bowl and an M&M. Have them fill each bowl with enough water to cover the M&M, and place the candy in the center of the bowl. Have the students observe the top layer of the candy as it dissolves, making sure to note the pattern the dissolving color forms around the M&M. The students can time it to see how long it takes, or set a time and see how much dissolves within the set period. Use this simple procedure as a lead-in to have students form their own experiments about different-colored candies. Have them create and write an experiment, and conduct their own test.
Pour 8 ounces of room temperature water into a container, and stir in a substance such as salt or sugar by adding 1 teaspoon at a time. Continue adding the substance until the water is saturated. Repeat the experiment in a separate container, but this time use 8 ounces of hot water instead of the room-temperature water. Students should keep track of how much of the material is added to each solvent. Have them compare the results to determine whether room-temperature water or hot water will dissolve more of the substance.
Before you start the experiment, have students predict which substances will dissolve in water. Then, provide students with powdered materials, such as sugar, salt, soap or baking soda, and liquid products, such as oil, soap or butter. Supply one plastic cup of water for each substance per student or group. Add one element to each cup and stir, observing the reaction to the water. Use the results of the experiments to lead the class into a discussion about substances that will dissolve in water; then discuss other solvents that can be used to dissolve the substances that remained undissolved. Other experiments may be conducted from the students' answers.
Dissolve sugar in water in a glass until the liquid is saturated. Tie a clean, white cotton string around a pencil. Place the pencil over the top of the cup, and let the string dangle down into the solution. Then set the experiment in a safe place, and allow the water to evaporate. As the water leaves, many of the sugar crystals will cling to the cotton string. This tasty experiment demonstrates how you can reverse the effects of dissolving sugar in water.