Date
Name
Section
Due Date:
Qualitative Observations of a Chemical Reaction
Lab 1
Pre-Lab Discussion
Scientists rely heavily on experimentation. A good scientist must observe and interpret what is happening.
Observing means using the senses: seeing, smelling, touching, hearing, and sometimes tasting. NEVER TASTE
CHEMICALS UNLESS INSTRUCTED TO BY YOUR TEACHER.
When scientists make observations, they try to be objective. Being objective means putting aside any
preconceived notions. Scientists are interested in what really occurs, not in what they wish would occur.
After observations are made, scientists must make interpretations. Interpretations are based on previous
knowledge and experience. Because people have different experiences, one scientist may interpret observations in
one way while another may interpret the same observations to mean something else. When we interpret, we
attempt to make sense out of observations. Scientists never assume that their interpretations are correct until they
test them fully and repeatedly. After complete testing, scientists then come to their conclusions.
In this investigation, you will make some qualitative observations of a chemical reaction. That is, no
measurements will be made. During a chemical reaction, one or more substances change into one or more other
substances. The burning of wood, wax, oil, gasoline, and coal are examples of a chemical reaction known as
combustion. The reaction you will study in this investigation is a combustion reaction.
LAB TIME: 30-40 minutes
Purpose
Carefully observe and interpret a chemical reaction.
Equipment
beaker, 250-mL
Erlenmeyer flask, 125-mL
glass square microspatula
metric ruler
microslide-(like used in biology)
parafilm
safety goggles
lab apron or coat
graduated cylinder
Materials
candle (2-cm diameter)
matches, a box
toothpicks, 2
limewater solution
string- only cut what you need; do not waste supplies
aluminum foil
cobalt chloride paper- keep this paper in the closed container until you are ready to use
it. It is hydroscopic ≈ readily takes up water
Safety
In this experiment, you will be working with an open flame. Tie back long
hair and secure loose clothing. Also, wear safety goggles and a lab
apron or coat at all times when working in the lab. Be sure all matches and
burned materials are completely extinguished before they are discarded.
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Procedure
Record observations for each step.
1. Note appearance, odor, and feel of the unlighted candle.
2. Heat the bottom of the candle and secure it to a glass square on your lab bench.
Light the candle and allow it to burn for several minutes. Note any changes.
Briefly describe the burning candle.
3. Blowout the flame and immediately place a lighted match in the "smoke" about
2 cm above the wick. See Figure 1-1. Note the result.
Figure 1-1
4. Use a microspatula to transfer a small amount of liquid from the bowl of the
candle onto a microslide. Try to light it and note the result.
5. Place a toothpick into the soft candle next to the unlighted wick to form a wooden
wick. Light the toothpick and note the result.
6. Place a length of string about 4 cm long on the glass square. Light it and observe
its behavior.
7. Make a slit in a small piece of aluminum foil. See Figure 1-2. Light the candle.
Place the foil between the base of the flame and the liquid in the candle bowl. Note
the behavior of the flame.
aluminum foil
Figure 1.2
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Note:
You may want to use a
hot-hand instead of the
tongs.
Figure
1-3
8. Invert a 250-mL beaker over the lighted candle. See Figure 1-3. Note any
substance that collects on the inside of the beaker. Test the liquid that condenses on
the beaker with cobalt chloride paper. *Try to char the bottom of the beaker-if you do
this must be cleaned thoroughly at the end of the experiment.
9. Invert a 125-mL Erlenmeyer flask over the lighted candle for several minutes.
Remove the flask, turn it right side up, and add about 10 mL of the clear limewater
solution. Stopper and shake the flask. Note any change in the limewater solution.
Observations and Data
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Conclusions and Questions
1. What phases (solid, liquid, gas) are present in the unlighted candle? In the burning candle?
Which phase(s) appear to take part in the chemical reaction?
2. What part does the wick play in the burning of the candle? What properties should the wick
have? Explain the result when aluminum is placed between the liquid and the wick. Is the wick
part of the chemical reaction? You may want to research this answer-do not guess!
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3. What two substances are indicated by the cobalt chloride and limewater tests respectively? Is it
possible that other substances are produced when the candle burns? How can you tell? Explain.
4. A source of energy is needed to start the burning of the candle. What energy source is used? Did
the reaction give off (exothermic) or absorb heat (endothermic)?
5. Give an example illustrating the difference between observation and interpretation based
on this lab and your knowledge of science..
NOTE:
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A conclusion should always be
written for a lab. Please write and
attach.
Your instructor may want this
typed.