Chemistry in a Ziploc Bag:
Mini-lesson
Vanderbilt Student Volunteers for Science
Spring 2014
I. Introduction
•Tell students this lesson involves a chemical
reaction that produces a gas. Warn them that
the ziploc bag is going to fill up with air.
•Assure students that the chemicals are safe.
•For this experiment, students work in pairs.
I. Preparation
• Count students. Prepare enough cups for
students to do the experiment in pairs.
• Pour 15 mL phenol red into 2oz cups (to the
marked line).
• Explain to students the importance of making
careful observations and recording them.
II. Experiment
•Give each pair one ziploc
bag containing baking
soda, one 2oz cup
containing 15 mL of phenol
red solution, and one plate.
IIb. Experiment
• One of the students
should hold the bag
upright over the pan
while the other adds the
15 mL of phenol red
solution to the bag.
• The student holding the
bag should seal it.
• Have the students feel
the closed bag and
record observations.
IIc. Experiment
•Tell students to have the bag open
and over the plate for a VSVS
member to put in one spoonful of
anhydrous calcium chloride.
•Have two VSVS members go
around with a plastic spoon to put
one spoonful in each bag.
•The student holding the bag should
seal it as quickly as possible after
the calcium chloride is added.
IId. Experiment
•The student holding the
bag should keep it
upright and sealed while
gently shaking back and
forth.
•The reaction takes 3 to
5 minutes to go to
completion.
•Make sure students
record their
observations.
III. Possible Student Observations
(1) When phenol red solution is added to the
baking soda bag, it remains red.
(2) The bag feels cold.
(3) When the calcium chloride is added, the phenol
red turns yellow. Students may feel a shortlasting warming while the anhydrous calcium
chloride dissolves in water.
(4) The bag fills up with gas and continues to feel
cold.
Explanation For Students
• Phenol red is an acid-base indicator which turns red in
basic solution and yellow in acidic solution.
• The bag feels cold because baking soda absorbs heat
when it dissolves in water.
• When the anhydrous calcium chloride, the mixture
becomes warm at first because anhydrous calcium
chloride gives off heat when it dissolves in water.
• The phenol red solution then turns yellow which
indicates an acidic solution.
• The bag fills with carbon dioxide gas (see manual).
• The bag continues to feel cold because heat is being
absorbed.
Evidence for a Chemical Reaction
• Tell students what evidence to look for to determine if a
chemical reaction occurs: a color change, a gas given
off, temperature change, or the formation of a
precipitate.
• Ask the students what evidence for chemical changes
did they observe in today’s experiment?
• Answers:
– A color change.
– A gas given off.
– A temperature change.
Clean Up
• In the event one bag leaks or explodes, use
paper towels to clean up any mess.
• The VSVS team should collect all Ziploc bags
and used cups, and put them in the trash bag.
• Make sure the Ziploc bags with the reaction
mixture is sealed before you put them in the
trash bag.
• Put everything else in the kit box along with the
trash bag and return it to the VSVS lab.