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LAB in Solubility, Physical Change, Solute & Solvent. Last updated November 15, 2018.
Summary
In this lab, students will prepare a solution to observe a physical change.
Grade Level
Middle school or High 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
- 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 make this lab more inquiry based, allow students to experiment with the ingredients to find the correct ratio. Guide them, if needed, but allow them to explore as much as possible. Give each group the correct amount of three of the reactants and have them experiment with the optimal amount of the fourth.
- To help students properly cut out the tree parts, you could make a template ahead of time. The tree should look something like:
For the Student
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
- petri dish
- plastic spoon
- cup of table salt
- laundry bluing (will stain)
- tray
- ammonia
- food coloring
- scissors
- hot water
- stirring rod
- large plastic cup
Procedure
DAY 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.
- 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)
- Gently, stir the solution in the cup.
- Place a petri dish on a tray. Label your tray by writing your name on masking tape and sticking the tape to the tray.
- Pour the solution into the petri dishes. Use the spoon to transfer any remaining solid in the plastic cup into the petri dish.
- Place your tree in the petri dish so it stands.
- Place only 1 drop of food coloring at the tip of one “tree branch.”
- Make observations of your tree. Store it somewhere safe so you can make observations the next time you have class.
DAY 2
- Obtain your tree. Make observations. Draw what your tree looks like now.
- Throw out the tree. Clean and dry the petri dish
Observations
Day 1:
Day 2:
Analysis
Answer these questions in complete sentences.
- How did the salt get on the chemistree?
- Explain how the salt crystals formed on the edges of the tree.
- Why did it take so long to occur?
- Use your textbook: Define the word crystal.
- 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