Name: ___________________________________________ Per: ____
U2L9 Sunrise in a Bag Lab
In this series of experiments, you will make qualitative observations as calcium chloride (CaCl2) and sodium
bicarbonate (NaHCO3) react in the presence of water and the acid/base indicator Phenol Red in a complex
reaction. The overall chemical equation can be written as follows, though intermediate products are not
shown:
CaCl2(aq) + 2NaHCO3(aq) + phenol red (basic form) → CaCo3(s) + 2NaCl(aq) + H2O(aq) + CO2(g) + phenol red (acidic form)
*(aq) = aqueous (dissolved in water)
Part A
1. Record your observations before, during and after the reaction in the tables below.
•
What are some observable properties of the reactants?
Reactant
Observations
Calcium chloride
Sodium bicarbonate
Phenol Red (basic form)
2. Place the following three substances in separate locations (do NOT allow them to mix…see diagram at
right) in a sealable plastic bag that is lying flat on the table.
a. 1 tablespoon of calcium chloride (1 full plastic spoon full)
b. 1 teaspoon of sodium bicarbonate (approx. 1/3 of a plastic spoon full)
c. 10 mL of phenol red indicator solution
3. Carefully seal the bag and grasp the bag at each bottom corner above the calcium chloride and sodium
bicarbonate so that they cannot mix with one another. The phenol red, however, should come into
contact with both now!
•
What happens at the corners of the bag? (Sight and touch!)
Sodium bicarbonate + Phenol Red(aq):
Calcium chloride + Phenol Red(aq):
4. Now release the corners of the bag and allow everything in the bag to mix by gently rocking the bag.
•
What happens when all the reactants are mixed together? (Sight and touch!)
•
What do the contents of the bag look like after the reaction has completed?
5. Finally, carefully open the bag while making sure that the opening is aimed away from yourself and
anyone around you. Allow the bag to remain open and the gas to escape. After about a minute, record
your observations below and describe what your observations before and after opening the bag
suggest.
Part B
How can we find out what interactions are responsible for the observed changes?!?
1. After Part A, you should have some questions about what is actually going on in the sealed plastic bag.
Formulate at least three questions that still need to be answered after Part A. (Hint: think about the
changes you observed)
2. Data Table 1 on the next page will give you some guidance as to which controlled experiments we need
to perform in order to better understand what interactions are causing the temperature, gas, and color
changes that we observed in Part A.
a. Use the same quantities of chemicals as in Part A to carry out the seven controls.
b. If water is tested in a controlled experiment, use the same amount of water as of phenol red
solution in Part A.
c. After each controlled experiment, record your observations in Data Table 1 and indicate
whether it was a physical or chemical change (careful!).
Data Table 1
Number
(Reaction
container)
Calcium
chloride
Sodium
bicarbonate
Phenol
red
Water
Observations
Physical
or
Chemical
Change?
1
(small
beaker)
2
(ziploc
bag)
3
(ziploc
bag)
4
(ziploc
bag)
5
(ziploc
bag)
6
(small
beaker)
7
(ziploc
bag)
Discussion Questions
1. What control experiments were done to evaluate if a liquid is necessary for the observed effects in Part
A? Does any reaction occur in the absence of water?
2. Is there any evidence that a new chemical substance is produced in the overall reaction of the four
substances mixed in Part A? Explain. What interaction among the four components must be
responsible for the new substance?
3. Based on the results of the control experiments, what interaction among the four substances seems to
be responsible for the observed temperature change in the overall reaction in Part A? Was this
interaction a physical or chemical change?
3. Temperature changes are sometimes used as evidence to indicate that a chemical change/reaction,
which produces a new chemical substance, has occurred. Comment on using this observation as an
indication of a chemical reaction.
Complete the following paragraph explaining what took place in the bag. Use the word bank to help you;
not all words will be used!
acidic acids bases
endothermic exothermic
basic chemical change color
gas physical change red yellow
Calcium chloride produces heat (___________________) when dissolved in water, while sodium
bicarbonate absorbs heat (___________________) when dissolved in water. Calcium chloride, baking
soda, and water combine to produce carbon dioxide __________. Phenol red is an acid/base indicator
that changes __________ in the presence of ___________ and ____________. This change in color
indicates a _________________________. Sodium bicarbonate (baking soda) is a base. When it comes
into contact with phenol red in its basic (red) form, the phenol red keeps its bright ________ color. As
sodium bicarbonate reacts with calcium chloride in water, acidic substances are produced and the
phenol red indicator changes from its basic form to its acidic, or __________, form. Carbon dioxide is
one of the acids produced—it dissolves in water and reacts to form carbonic acid, H2CO3, which makes
the water acidic. (This is also why unflavored, unsweetened sparkling water tastes sour!) If some of this
carbon dioxide gas is allowed to escape from the bag, less of it will remain dissolved in water and the
water will become less ___________ (more ___________) again and the contents of the bag may turn
slightly orange or pink again.