Name________________________________
Qualitative Observations of a Chemical Reaction
Scientists rely heavily on experimentation. A good scientist must observe
and interpret what is happening. Observing means using all your senses: sight,
smell, touch and hearing.
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
reaction you will study in this investigation is a combustion reaction.
Purposes:
To carefully observe and interpret a chemical reaction.
Materials:
safety goggles
Wooden splint
Erlenmeyer flask-125 mL
Glass square
Candle
String
Matches
Toothpick
Limewater solution
Aluminum foil
Cobalt chloride paper
rubber stopper
graduated cylinder-10 mL.
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Procedure:
Record observations for EACH step in the table below
1. Note appearance, odor, and feel of the unlit candle and record at least
5 observations in Table 1.
2. Heat the bottom of the candle and secure it to a glass square. Light the
candle and allow it to burn for several minutes. Note any changes. Briefly
describe the burning candle and record at least 5 observations in Table 1.
3. Blow out the flame and immediately place a lit match into the “smoke”
about 2 cm above the wick. Record the result in Table 1.
4. Use a wooden splint to transfer a small amount of liquid wax from the top
of the candle onto a glass plate.
5. Try to light this with a match and record the result in Table 1.
6. Place a toothpick into the soft candle next to the unlit wick to form a
wooden wick. Light the toothpick and record the result in Table 1.
7. Place a length of string about 4 cm long on the glass square. Light it and
observe its behavior. Record result in Table 1.
8. Make a slit in a small piece of aluminum foil. 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 in Table 1.
9. Pour about 10 mL of clear limewater into a 10 mL graduated cylinder and
set this aside until the next step. Goggles are absolutely necessary.
10. Invert a 125 ml Erlenmeyer flask over the lighted candle for several
minutes to collect as much candle “smoke” as you can. Remove the flask,
turn it right side up, and pour in the clear limewater solution. Stopper and
swirl the flask. Record any change in the limewater solution in Table 1.
11. Place a 400 mL beaker over the flame to collect some of the product.
Rub a piece of cobalt chloride paper on the inside of the beaker. Record
the result in Table 1.
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TABLE 1: _________________________________________________________________
Unlit candle
Lit candle
Lit match in
smoke
Wax on glass
Toothpick
String
Aluminum foil
Limewater
Cobalt chloride
paper
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Questions (answers to these will be typed in FULL SENTENCES:
1. What phases (solid, liquid, gas) are present in the unlit candle?
2. What phases are present In the burning candle?
3. What part does the wick play in the burning of the candle?
4. What properties should the wick have?
5. Explain the result when aluminum is placed between the liquid and the wick.
6. Is the wick part of the chemical reaction? Relate this to your results from step
7 with the string.
7. What product is indicated by the cobalt chloride paper? What is the resulting
color of the paper when that substance is present?
8. What product is indicated by limewater? What happens to limewater when
that substance is present?
9. Is it possible that other substances are produced when the candle burns?
Explain.
10. A source of energy is needed to start the burning of the candle. What
energy source is used?
11. Did the reaction of the burning candle give off or absorb heat?
Conclusion:
Describe reactants and products of a burning candle, telling how you knew
each product was produced. Look up the chemical composition for wax and
include was as a reactant.
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