Salt is a desiccant: It absorbs or removes water. Examine this property with your students using two lettuce leaves patted dry, two paper towels and salt. Put a lettuce leaf on each paper towel and sprinkle 1/8 teaspoon salt over one of the leaves. Wait 20 minutes. The paper towel is wet because the salt pulled water out of the salted lettuce leaf. In the human body, salt and potassium are used by the kidneys to balance fluid levels. Salt takes water from tissues and puts it into the bloodstream.
Salt is a mineral with a crystal form. Have your students use a magnifying glass to examine the cube shape of some table salt. Give each student a small clear plastic cup. Have students put 15 milliliters of salt into the cup, weigh the cup and record the result. Tell them to fill the cup one-third full with hot water, stir until the salt dissolves and mark the salt water level. Have students predict what will happen when the water evaporates. Check the cups daily. When the water evaporates, weigh the cup. Have the students use a magnifying glass to examine the structure of what remains in the cup.
Help your students explore the reason salt is spread on icy sidewalks and roads. Give each student a cup of warm water. Measure a different amount of salt for each student to add to the cup. Have them label the cup with the amount of salt used and stir the water until the salt dissolves. Label a cup of water as the control. Put all the cups in a freezer and check them every 15 minutes. Record the time the water in each cup freezes. Discuss the results.
Ask your students if it's easier to float in fresh water or salt water, and if anyone knows the reason why. Experiment with density to help them answer this question. Each student should fill two identical containers with water, label one container "Salt Water" and add to it six tablespoons of salt. Stir it until the salt dissolves. Tell them to put an uncooked egg in the nonlabeled container and observe what happens. Then they should put another uncooked egg into the salt water container and observe. Discuss why the salt makes the water denser.