Lab: Chemistree FOR THE TEACHER Summary In this lab, students will prepare a solution to observe a physical change. Resource Type Lab
Submitted by: Chris Herald USD 383 in Manhattan, Kansas
Grade Level Middle school
Objectives By the end of this lesson, students should know the parts of a mixture. understand that a mixture can be separated by physical means. Chemistry Topics This lesson supports students’ understanding of Physical changes Solutions Solute/solvent Time Teacher Preparation: 40 minutes Lesson: 2 45 minute class periods Materials For each group: blotter paper petri dish plastic spoon cup of table salt laundry bluing (will stain) tray
ammonia food coloring scissors hot water stirring rod large plastic cup
Safety Always wear goggles when working in a lab. Make sure students handle hot water carefully. Students should wash their hands thoroughly before leaving the lab. When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals. Vocabulary Terms crystal solid solute
solution evaporation liquid
solvent
Teacher Notes Heat water on a hot plate for the class ahead of time. The activity is started one day and must sit overnight so the water can evaporate. To help students properly cut out the tree parts, you could make a template ahead of time. The tree should look like the photo on the right.
FOR THE STUDENT Student Activity Sheet: Chemistree Lab: Absorption & Evaporation Lesson Background In this activity, you will prepare a mixture with four different substances. After the solid salt is dissolved in the liquids, the blotter paper will absorb all parts of the solution. This allows the salt to travel up and through the paper. Overnight, the liquids, which are the solvents, will evaporate. The salt is the compound sodium chloride, which has ionic bonds and is normally a cube-shaped crystal. The tiny particles of the bluing act as “seed” particles around which the salt crystals form. Thus, the resulting crystals look very different than the original sodium chloride. Sodium chloride, which is the solute, will remain as fine crystals on the edges of the tree. Because evaporation occurs fastest on the edges, this is where many of the crystals will form on the chemistree. This process is an example of a physical change because the salt dissolves and recrystallizes. Materials blotter paper cup of table salt ammonia hot water
petri dish laundry bluing (will stain) food coloring stirring rod
plastic spoon tray scissors large plastic cup
Procedure DAY 1 1. Cut two pieces of blotter paper in the shape of a tree. Cut a slit from the bottom to the middle of one tree. Cut a slit from the top to the middle of the other tree. Insert the two papers to from a tree that stands on its own. 2. With another group, prepare a special solution. In the large plastic cup, add the following chemicals in the order in which they are listed below: table salt (6 spoons) hot water (6 spoons) ammonia (1 spoon) laundry bluing (6 spoons) 3. Gently, stir the solution in the cup. 4. Place a petri dish on a tray. Label your tray by writing your name on masking tape and sticking the tape to the tray.
5. Pour the solution into the petri dishes. Use the spoon to transfer any remaining solid in the plastic cup into the petri dish. 6. Place your tree in the petri dish so it stands. 7. Place only 1 drop of food coloring at the tip of one “tree branch.” 8. Make observations of your tree. Store it somewhere safe so you can make observations the next time you have class. DAY 2 9. Obtain your tree. Make observations. Draw what your tree looks like now. 10. Throw out the tree. Clean and dry the petri dish Observations Day 1: Day 2: Analysis Answer these questions in complete sentences. 1. How did the salt get on the chemistree? 2. Explain how the salt crystals formed on the edges of the tree. 3. Why did it take so long to occur? 4. Use your textbook: Define the word crystal. 5. Name two edible crystals. Bonus. What is the purpose of the bluing? Conclusion Explain what occurred in this experiment using ALL of these vocabulary words and underline each word in your explanation. crystal, solid, solute, solution, evaporation, liquid, solvent
