Which is sugar and which is salt?
Objectives:
Students use the senses to observe and distinguish differences. Students see and describe how evaporation leaves crystals that are different for sugar and salt.
Focus:
Scan for prior knowledge by asking the students to describe how we learn by the senses. Show the students two clear glasses with some sugar in one and salt in the other. Ask them to predict which is which. They will answer as if they know and ask them ," How do you know?" Guide them to the idea that we cannot tell without help (magnifying glass or microscope) unless we can taste or smell them. They feel and look the same. If the students discover which is which while handling the crystals, mix up your glasses again behind a blind so that no one knows - even you!
Have them take a deep breath and ask them if they think there is water in the air. Challenge them- water in the air is called water vapor and I can prove it to you in just a few days. Watch and I'll show you!
Materials:
Procedure and Monitoring:
Dissolve the sugar and salt in the glasses. Make the solution a little thick, to the point that almost no more can be dissolved. Ask the students if they can tell now which is which. (They still cannot). Have the students write down a guess as to which glass has sugar and which has salt. Have your materials managers pass out all the petri dishes. Divide the class into equal groups and designate one side A and the other B. Pour just a teaspoon of the sugar solution into all the petri dishes on side A and pour just a teaspoon of the salt solution for everyone on side B. (It doesn't matter which is A or B at this point as long as all A's are one solution and all B's are the other)
Now have students predict (through inventive spelling or copying) what will happen. What will we see in the dishes a few days from now? Have each student PREDICT whether or not the solution will change or stay the same.
When the water in the solution evaporates a crystal pattern will randomly occur in the dishes. Kids love the sight of it. Look for the differences by using a magnifying glass or microscope. Taste the crystals!!
Close :
NOW WHERE DID THE WATER GO? The sugar and salt are still there in the dishes but the water is not. Water in the air is called WATER VAPOR.
Summarize what we've seen and answer our guesses in the journals. How do we use the senses to learn? What is water vapor?
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