Investigation a Chemical Reaction
The chemicals used in this investigation are: calcium chloride, a compound used to melt
ice, sodium bicarbonate, better known as baking soda, and phenol red (a dye dissolved in
water), an acid/base indicator. Water is also present as the solvent in the solution of
phenol red.
Four different ingredients can be mixed in different combinations. Three are pure
substance (calcium chloride, sodium bicarbonate, and water “sort of”) and one is a
homogenous mixture or solution.
On your lab report, describe the substances you will be using in your lab report as a
substance or homogeneous mixture.
calcium chloride_______________
phenol red ____________________
sodium bicarbonate_____________
water _______________________
In your group (of 3 or 4 persons), carry out the following procedure. Record your
observations on your own lab report.
Procedure:
a. Mix one teaspoon of calcium chloride and 1/2 teaspoon of sodium bicarbonate in a pint
sized ziplock bag. Make careful observations and describe any changes on your lab
report.
TABLE: Make this table and record your observations.
Mixture
(from step a) NaHCO3
and CaCl2
(from steps a to c)
NaHCO3 and CaCl2
phenol red.
Centrifuge the
combination of NaHCO3
and CaCl2 phenol red.
NaHCO3 and phenol red
CaCl2 and phenol red
NaHCO3 and CaCl2 and
water.
Observations.
b. Pour 15 mL of phenol red into a small vial. Place the vial inside the ziplock bag in a
manner not to spill the liquid onto the other ingredients. Remove the air from the bag
before closing it.
c. Manipulate the ziplock bag to cause the phenol red to mix with the calcium chloride
and the sodium carbonate. Make careful observations and describe any changes.
Record your careful observations on the table.
d. Half-fill a 13x100 mm test tube with the liquid product. Fill a second test tube with
water to the very same level as the first. Place the two tubes opposite one another into
a centrifuge. Follow your instructor’s direction on centrifuge usage.
e. Once the reaction has stopped, remove some of the liquid from the bag into a beaker
and set aside while you continue. Clean out old bag.
f. There are three more experimental mixtures shown in the table. Within your group
divide the work so the remaining three experiments are completed at the same time.
The purpose of these additional experiments is to determine which substance was
responsible for each change such as color change. Use the mixture shown in the table.
Each time you l use calcium chloride use 1 teaspoon and each time you try sodium
bicarbonate use 1/2 teaspoon and each time you use phenol red use 15 mL
Questions:
1. What is the difference between a substance and a mixture?
2. What were the signs that a chemical reaction occurred in the mixture involving
NaHCO3 and CaCl2 phenol red?
3. What information was clearly identified by centrifugation?
4. Which combination of chemicals produced
a.
b.
c.
d.
Gas production (bubbles)
Precipitation (ppt)
Change in temperature (∆T)
Change in color
5. What other sign or change may accompany a chemical change?
Write a summary.