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Benzoic Acid Blizzard in a Bottle (2 Favorites)

LAB in Solubility. Last updated May 30, 2017.


Summary

In this lab, students create a snow globe by taking advantage of benzoic acid’s solubility properties in hot water.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

  • write the chemical equation for benzoic acid.
  • identify a compound as either ionic or covalent.

Chemistry Topics

This lesson supports students’ understanding of

  • Solutions
  • Solubility
  • Solute/solvent

Time

Teacher Preparation: 25­–30 minutes

Lesson: 40–55 minutes

Materials

  • 250-mL beaker
  • Water
  • Benzoic acid
  • Glass stirring rod
  • Beaker tongs
  • Baby food jar
  • Electrical tape
  • Small figuring or ornament
  • Ribbon (optional)
  • Fabric (optional)

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • 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.

Teacher Notes

  • Have another assignment for students to work on while they wait for their solution to cool.

For the Student

Lesson

Background

A solution is formed by dissolving a solute, such as benzoic acid, in a solvent, such as water. A saturated solution contains as much solute as possible at a given temperature and pressure. A solution is said to be unsaturated when it contains a lower concentration of solute than a saturated solution. When the temperature is increased, the solubility increases and more solute will dissolve. If a hot, saturated solution is then cooled, the “extra” solute that dissolved with the added heat will precipitate. This is the chemical phenomenon that occurs when the benzoic acid precipitates out as “snow” in this lab.

Materials

  • 250-mL beaker
  • Water
  • Benzoic acid
  • Glass stirring rod
  • Beaker tongs
  • Baby food jar
  • Electrical tape
  • Figurine or ornament
  • Ribbon (optional)
  • Fabric (optional)

Procedure

  1. Slowly heat 100 mL of tap water in a 250-mL beaker using a hot plate. Do not allow the water to boil.
  2. As the water is heating, add about 1 g of benzoic acid. Continue to heat and stir the mixture until the benzoic acid completely dissolves. The solution should not come to a boil. Turn off the hot plate.
  3. Using the beaker tongs, remove the beaker from the hot plate and allow the solution to cool on the lab bench. Leave the glass stirring rod in the beaker.
  4. Keep an on eye on the benzoic acid solution as it begins to cool. Snowy-looking crystals will appear. Slowly stir the benzoic acid solution.
  5. While the solution cools, attach a figurine or an ornament to the inside of the baby food jar lid.
  6. After the solution has completely cooled to room temperature, stir the snow mixture and quickly pour it into the baby food jar.
  7. Use a water bottle to fill the jar to the brim with tap water. Leave as little air as possible in the jar.
  8. Cap the jar tightly. Turn the snow scene upside down and watch your figurine get buried in the blizzard of benzoic acid “snow.”
  9. Use electrical tape to seal the jar lid completely. Secure a piece of fabric on the lid with a rubber band and then tie a ribbon.

Analysis

  1. Write the chemical formula for benzoic acid and draw the structural formula for it. Is it ionic or covalent?
  2. Why is benzoic acid resistant to dissolve in water?
  3. What is the most important reason for NOT allowing the water mixture to boil?