Observation and Experimentation: A Qualitative Analysis
Pre-Lab:
Read over the Lab report and set up the lab notebook with
 Title
 Partner
 Objective
 Data
Introduction:
“The world is full of obvious things, which nobody by any chance ever observes.”
This quote, from Sherlock Holmes, discusses the importance of careful
observation in detection. Careful observation is also the foundation of chemistry as an
experimental science, leading us to question what we have observed. How, What, and
Why? The answers to these questions are sought in experiments, which may be
described as observations made under controlled condition. Controlled experiments
make it possible to separate or isolate the factors that are responsible for a given
observation in a complex series of events. Therefore, it becomes evident that observation
and experimentation are the twin pillars of the scientific method.
In this laboratory experiment, three substances - solid sodium bicarbonate, solid
calcium chloride, and a solution of phenol red in water - are placed in a closed container.
Upon mixing, a complex series of changes is observed. Observations include
temperature changes, color changes, and changes in state. How can we learn more about
the individual interactions responsible for each observation?
Background Information:
 Define the scientific method and describe how it relates to this lab experiment.
 Discuss how observations and experiments are necessary parts of chemistry.
 What is a control experiment and why did we need to use them?
Procedure:
1. Begin with a clean, dry bag. Place 1 scoop of calcium chloride in the bottom left
corner of the bag. Place 1 scoop of sodium bicarbonate in the bottom right corner
of the bag. Be careful to not let them mix yet!
2. Carefully add 2 droppers full of phenol red in the center of the bag.
3. Seal completely, and allow the chemicals to mix.
4. Record all observations.
5. Rinse and dry the bag thoroughly.
6. Invent some control experiments that will help you to come to an understanding
of what happened in the observed reaction. Perform these experiments and record
your results in the data table.
Questions:
1. Based on the results of the control experiments, what interaction among the
substances seems to be responsible for the observed temperature change in the
overall reaction?
2. Was there a temperature effect observed in any of the control experiments that
was NOT observed in the overall reaction of the chemical substances? Explain.
3. What color change was observed in the overall reaction of the substances? Do the
control experiments provide any evidence concerning the interaction(s)
responsible for the observed color change? If so, what are they?
4. Is gas bubble formation something that can occur separately from color change
and temperature change, or are the reactions linked?
5. Is there any evidence of a chemical change in the reactions you observed?
Describe how you could tell.
6. Let’s assume that the chemical identity of calcium chloride is not changed when it
is mixed with water. Suggest an experiment that could be done to prove or
disprove this hypothesis.
Observations
Calcium
Sodium
Phenol
Chloride
Bicarbonate Red
Water