Materials Included In Kit

Additional Materials Required

Prelab Preparation

Some manufacturers list the chemical contents of the toy on the back of the package. Look at the backs of the bags to see if the ingredients are listed. If they are, black out the print using a fine-tip black permanent marker or a strip of electrical tape.

Safety Precautions

Wear goggles and instruct students to wear goggles when demonstrating how the toy works prior to the student lab activity. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The contents of the spot plate may be flushed down the drain with excess water of according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Two toys are supplied for use as a demo to be done before starting the lab to familiarize students with the toys. Activate the bag by locating the water pouch inside the bag and squeezing it until it breaks. Give the bag a quick shake, drop it in a sink or bucket, and step back and wait for it to pop! Both parts of this laboratory activity may reasonably be completed in one 50-minute class period. The data compilation and Post-Lab Questions may be completed the day after the lab.
• Toy “Bomb Bags^™” are simple, harmless toys containing small amounts of two household chemicals. They do not pose any danger or threat and cannot be “scaled up” to create potentially dangerous devices.
• Place the universal and rainbow indicator in a central location in the classroom since all students will need access to them. You may wish to remove the “dropper top” for easier pipet access. Alternatively, fill 15 pipets with universal indicator and 15 pipets with rainbow indicator prior to the lab period and place them bulb down (tip towards the ceiling) at each lab station.
• For an advanced chemistry class, you may allow students to design their own procedure for determining the contents of the toy.
• The back of the toy mentions noticing a “fragrance” after the bag pops. A fragrance was not noticed during our testing.

Teacher Tips

• The “magic water” solution is simply a small pouch containing an aqueous solution of citric acid. The volume varies from 2.5 to 4 mL. The solid material in the toy is sodium bicarbonate, typically around 3 g. When pressure is applied to the pouch containing the citric acid, it breaks and therefore allows the citric acid solution to react with the sodium bicarbonate solid. Carbon dioxide is a byproduct of the following reaction:

  3NaHCO₃ + H₃C₆H₅O₇ → 3H₂O + 3CO₂ + Na₃C₆H₅O₇
  When the volume of carbon dioxide gas produced in this reaction exceeds the volume of the bag, it pops.

Sample Data

Weight of unknown solid ___3.4___ g

Volume of “magic water” ___3.1___mL

1. Observations—Evidence of chemical reaction—bubbling, foaming, frothing
2. Universal indicator color—Green
3. pH—7

1. Observations—Evidence of chemical reaction—bubbling, foaming, frothing
2. Rainbow indicator color—Green
3. pH—7

Answers to Questions

1. What was the purpose of using two different indicators in this lab? Hint: See the following pH charts.

   Universal indicator has a pH range of 4–10, whereas rainbow indicator has a pH range of 1–7. Samples with a pH lower than 4 do not give an accurate reading using universal indicator. Rainbow indicator must be used to find actual pH of acidic solution.

2. Use the following keys to fill in the pH values for well 10 in the following table. Universal indicator—Wells 1, 3, 5, 7 and 9
   {13546_Answers_Table_2}
   Rainbow indicator—Wells 2, 4, 6, 8 and 10
   {13546_Answers_Table_3}
   {13546_Answers_Table_4}
3. Did you notice any trends or patterns for the pH values in the wells?

   Well 2, magic water and rainbow indicator, and well 6, citric acid and rainbow indicator; also, well 3, unknown solid and universal indicator, and well 7, sodium bicarbonate and universal indicator appeared to have the same pH.

4. What purpose did wells 9 and 10 serve, which only contained water and indicator?

   These wells served as a control. Since all of the wells contain water, having a well with only indicator and water shows that water has a neutral pH around 7.

5. Based on the indicator color changes in wells 1–10, what chemical appears to be present in the “magic water” solution?

   The color changes and pH values for the magic water solution were very similar to citric acid. The magic water solution probably contains citric acid.

6. Is the pH of unknown solid acidic or basic? Identify the solid based on the results of other wells.

   The unknown solid was basic. Sodium bicarbonate was also basic with a pH around 8.

Introduction

Investigate the chemical contents in a popular toy to find out what makes it pop!

Concepts

• Acids and bases
• Scientific method
• Indicators
• pH

Materials

Safety Precautions

Citric acid, sodium bicarbonate and the contents of the Toy Bomb Bag^™ may be irritating to tissue and especially irritating to the eyes. Indicator solutions may stain skin and clothes. Avoid contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Shake the contents of the toy down to the bottom of the bag.
2. Carefully cut off a top corner of the foil bag using scissors.
3. With a gloved hand, pull out the “magic water” pouch from inside the bag.
4. Set the bag on a sheet of paper towel and set aside.
5. Place the weighing dish on the balance. Zero the balance.
6. Shake the remaining solid from inside the bag onto the weighing dish.
7. Record the mass of the unknown solid (to the nearest tenth of a gram) in the data table.
8. Using scissors, carefully cut off a corner of the “magic water” pouch and pour the contents into a 10-mL graduated cylinder. Squeeze the packet to get as much of the liquid out as possible. Record the volume (to the nearest tenth of 1 mL) in the data table. Note: Refer to Figure 1 for steps 9–24.
   {13546_Procedure_Figure_1}
9. Weigh out 1 g of citric acid in a weighing dish.
10. Weigh out 1 g of sodium bicarbonate in a weighing dish.
11. Using a pipet, dispense 10 drops of “magic water” from the graduated cylinder (step 8) into wells 1 and 2 and 2 drops of the magic water to well 11 of the spot plate.
12. Obtain approximately 5 mL of distilled water in a cup or beaker.
13. Using a clean pipet, add 10 drops of distilled water to wells 3–12 on the spot plate.
14. Using a microspatula, add an overflowing scoop of the unknown solid to wells 3 and 4 on the spot plate. Stir with a toothpick. Rinse the microspatula thoroughly with water.
15. Using a fresh microspatula, add an overflowing scoop of citric acid to wells 5, 6, and 12 on the spot plate. Stir with a fresh toothpick. Rinse the microspatula thoroughly with water.
16. Using a clean microspatula, add an overflowing scoop of sodium bicarbonate to both wells 7 and 8. Stir with a fresh toothpick. Rinse the microspatula thoroughly with water.
17. Using a fresh pipet, add two drops of universal indicator to wells 1, 3, 5, 7 and 9. Note: Do NOT touch the solutions with the pipet tip when adding the indicator.
18. Using a fresh pipet, add two drops of rainbow indicator to wells 2, 4, 6, 8 and 10. Again, do NOT touch the solutions with the pipet tip when adding the indicator.
19. In the data table, record the color of each well.
20. Well 11 contains a water and “magic water” mixture. Add an overflowing scoop of the unknown solid using a clean microspatula. Record observations on the data table.
21. Well 12 contains a water and citric acid mixture. Add an overflowing scoop of sodium bicarbonate using a clean microspatula. Record observations on the data table.
22. Add two drops of universal indicator to well 11.
23. Add two drops of rainbow indicator to well 12.
24. Record color changes for wells 10 and 11 in the data table.
25. The solutions in the spot plate may be flushed down the drain with excess water.

Student Worksheet PDF

13546_Student1.pdf