Chemistry in a Bag Demonstration

by Liz LaRosa

www.middleschoolscience.com

UPDATED 10/14/04

Objectives:

• to observe chemical reactions.

• to observe changes in pH.

• to do a burning splint test.

Materials:

* You can substitute  Phenolphthalein with Cabbage Juice if you have safety concerns or are doing this as a lab instead of a demo.  Follow instructions for Cabbage Juice as indicated.

SAFETY:  Always try the experiment yourself first and make sure that all the steps are followed so you know what to expect and can answer questions as they come up.

Procedure Bag 1:

1. Place 2 tsp of baking soda into the bag.

2. Add 30 mL of Phenolphthalein to the bag. (Skip this step if you are using Cabbage Juice)

3. Massage the bag to mix the contents.

4. VERY CAREFULLY - lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute). Do not let any spill out.

5. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.

6. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink. Cabbage Juice will turn greenish blue for a base and purple-ish for neutral, pink for acid

7. Pass the bag around and have students look at and feel the contents of the bag.  At this point, they will see the baking powder dissolving and the contents turning pinker.

Procedure Bag 2:

1. Place 2 tsp of calcium chloride into the bag.

2. Add 30 mL of Phenolphthalein to the bag. (Skip this step if you are using Cabbage Juice)

3. Massage the bag to mix the contents.

4. VERY CAREFULLY - lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute) Do not let any spill out.

5. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.

6. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink and start to get warm. Cabbage Juice will turn greenish blue for a base and purple-ish for neutral, pink for acid

7. Pass the bag around and have students look at and feel the contents of the bag.  At this point, they will see the calcium chloride dissolving and the contents turning pinker and getting warmer.

Procedure Bag 3:

1. Place 2 tsp of baking soda into the bag.

2. Place 2 tsp of calcium chloride.

3. Add 30 mL of Phenolphthalein . (Skip this step if you are using Cabbage Juice)

4. Massage the bag to mix the contents.

5. VERY CAREFULLY - lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute)  Do not let any spill out.

6. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.

7. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink. Cabbage Juice will turn greenish blue for a base and purple-ish for neutral, pink for acid

8. Pass the bag around and have students look at and feel the contents of the bag.  At this point, they will see the baking powder and calcium chloride dissolving, foaming, bubbling, instead of pink, it will become clear/white, and the bag will be warm.  As the bag is passed around, it will start to inflate and puff out.

At this point, you will have all 3 bags on your table.  You can have the students compare the 3 bags and discuss what is the same, what is different, why it was important that you did the same procedure for each bag etc.  Have students try to guess why the 3rd bag is puffy and not pink, etc.

Procedure - Part 2:

1. After you have discussed what happened in the three bags, have a student come up and light a match for you.

2. While you hold the wooden splint, have them light the splint with the match. 

3. Have another student hold the 3rd bag. 

4. Tell the student to open the bag then you will quickly place the burning splint into the bag. 

5. The flame will go out (even though the kids hope for a huge explosion!) and you can have them guess why it went out.

Observations Part 1:

Observations - Part 2

What happened when you placed the splint into the 3rd bag? Why?  ________________________________

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Analysis and Results:

1)   Was there a change in pH?  How do you know? __ _____________________________________

_______________________________________________________________________________

2)   What happened to the contents of the bags? ___________________________________________

_______________________________________________________________________________

3)   Without opening the bags, how can you tell if a gas was produced? __________________________

_______________________________________________________________________________

4)    This equation tells us what chemical reaction happened in the bag.  Identify and count the elements on each side of the "yield" sign:

2NaHCO₃ + CaCl₂ -----------> CaCO₃  + 2NaCl  + H₂O + CO₂

______________________________________________________________________________

______________________________________________________________________________

5)   Place a CIRCLE around the Calcium Chloride.  Place a SQUARE around the Salt. Place a TRIANGLE around the Water.

6)   What gas was produced in this reaction? ____________________________________________

7)   Was there a change in temperature?  How can you tell? ________________________________

_______________________________________________________________________________

Conclusion:

2-3 Sentences on what you learned.

Teacher Notes:

• You might want to double bag the bags if you pass them around. As the kid massage the bag, small tears in the bag may occur.  The 3rd bag may burst, it gets pretty full and tight.

• The Phenolphthalein turns pink in a base and clear for an acid/neutral.

• Cabbage Juice will turn greenish blue for a base and purple-ish for neutral, pink for acid

• Go over safety procedures for how to use matches, some students are afraid of matches or have never used them before.

• Do NOT  do a flame test for bags 1 & 2, it will ignite.  (Phenolphthalein is flammable)

• Click for MSDS info for  Phenolphthalein : https://fscimage.fishersci.com/msds/96382.htm

This lab was modified by Liz LaRosa from the original lesson:  http://www.science-house.org/learn/CountertopChem/exp5.html