University of Virginia
Physics Department

Crystallizing Borax

A Physical Science Activity

2003 Virginia SOLs

 

Objectives

Students will:

Motivation for Learning

Discuss with students the history of borax as given in the background information.

 

Background Information

Borax is sodium tetraborate. It dissolves in water forming an alkaline, antiseptic solution that is used as a water softener, disinfectant, detergent and welding flux. Historically, many ancient people found valuable uses for borax. The Egyptians used borax in mummification while the Romans used it for glass making. Marco Polo's caravans transported it from Tibet to Europe in the 13th century.

Borax was a rare commodity until lake bed deposits were found in California in the 1850s. The most famous commercial borax mining operations were located in Death Valley in California in the 1880s. Borax was recovered by dissolving "cotton balls" made up of borate minerals in boiling water. As the solution cooled the borax precipitated out. To get the borax to market was a165 mile journey through the hot desert to the nearest railroad. Up to ten tons of borax was carried on giant wagons that were pulled by teams of 18 mules and 2 draft horses - the famous "20-mule teams." These teams averaged two miles an hour; as a result the round trip took 30 days to complete. Click here for more information about the history of borax mining in Death Valley.

Notes to the Teacher: Mule Team Borax can be purchased at the grocery store in the section near bleach and detergents. Borax is potentially toxic to humans and pets, if ingested in large amounts. Students should wear safety goggles and wash hands thoroughly after contact.

Student Activity

To print out the Student Copy only, click here.

Materials

Procedure:

Part I - Making a pipe cleaner ornament

  1. Shape pipe cleaners into a design
  2. Attach pipe cleaner to a string
  3. Hang string from a pencil

Part II

  1. Use a graduated cylinder to add 700 ml of tap water to a 900 ml beaker
  2. Place empty 250 ml beaker on a balance and record its mass
  3. Add 250 grams of borax to the beaker and record the mass of the beaker and the borax to the nearest tenth of a gram
  4. Slowly add one teaspoon of borax to the water. Stir until all the borax has dissolved before adding any more borax.
  5. Continue to gradually add borax to the water until no more will dissolve after you have stirred the solution for two minutes. The solution is now saturated.
  6. Use a thermometer to record the final temperature of the saturated solution and record in the data table.
  7. Mass the beaker and the remaining borax and record.

Part III

  1. Heat the borax solution made in part I to 400C using a hot plate
  2. Once the solution has reached 400C, remove the beaker from the hot plate.
  3. Continue adding borax from the remaining cupful in part II. Stir in each teaspoon of borax until it has dissolved.
  4. Continue to gradually add borax to the water until no more will dissolve after you have stirred the solution for two minutes. The solution is now saturated.
  5. Mass the beaker and the remaining borax and record.

Part IV

  1. Place the beaker on the hot plate and heat the borax solution made in part II. Once the solution has reached 600C, remove the beaker from the hot plate using a hot pad.
  2. Continue adding borax from the remaining cupful in part III. Stir in each teaspoon full of borax until it has dissolved.
  3. Continue to gradually add borax to the water until no more will dissolve after you have stirred the solution for two minutes. The solution is now saturated.
  4. Mass the beaker and the remaining borax and record.
  5. Place the beaker on the hot plate and heat until the solution changes from cloudy to clear. Then remove from the hot plate using a hot pad.

Part V

  1. Gently lower the pipe cleaner ornament into the borax solution.
  2. Rest the pencil across the top of the beaker so that the ornament is suspended in the solution without touching the bottom or sides of the beaker. (three ornaments should fit in one beaker).
  3. Set aside for 24 hours.
  4. After several hours you should see crystals begin to appear. Remove the crystal ornament from the solution and allow it to air dry after the 24 hours.  

Data Sheet

To print out the Data Sheet only, click here.

  Initial Mass of Borax + Beaker Final Mass of Borax + Beaker Initial Mass - Final Mass = Total Mass of Borax Added Solubility = Borax (g)/water (ml)
Tap Water (~ 200C)        
Warm Water (~400C)        
Hot Water (~600C)        
In the space above, graph the temperature of the solution versus the solubility of the borax. Use the y-axis for tempertature and the x-axis for solubility.

 

Students with Special Needs

Each student should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

 

Assessment

To print out a copy of the Assessment only, click here.

1. How does temperature affect the solubility of a substance?

 

 

2. In this experiment, what was the solvent and what was the solute?

 

 

3. From your graph, how much borax would dissolve in 700 ml of water heated to a temperature of 50 0C?

 

 

4. From your graph, what temperature of water is required to dissolve 25 grams of borax?

 

 

5. If you were to make a borax solution for cleaning, would you use cold or warm water? Explain your answer.

 

 

6. At what point in your experiment was the solution unsaturated, saturated, and supersaturated?