Qualitative Observations of a Chemical Reaction
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.
Beaker 250 ml candle
(2 cm diameter) Paper towels
Erlenmeyer flask 125 ml
matches aluminum foil
Glass square toth
picks cobalt chloride paper
Record observations for
- Note appearance, odor, and feel of the unlit candle.
- Light the candle and allow it to burn for several
minutes. Note any changes. Briefly describe the burning candle.
- Blow out the flame and immediately place a lighted match
in the “smoke” about 2 centimeters above the wick. Note the result.
- Drip a small amount of liquid from the bowl of the
candle onto a microslide. Try to light it and note the result.
- Place a toothpick into the soft candle next to the unlit
wick to form a wooden wick. Light the toothpick and note the result.
- Place a length of string about 4 cm long on the glass
square. Light it and observe its behavior.
- 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.
- Invert a 250-mL beaker over the lit candle. See Figure
1-3. Note any substance that collects on the inside of the beaker. Test the
liquid with cobalt chloride paper.
- Invert a 125-mL Erlenmeyer flask over the lit 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.
- Place the copper coil around the lit wick. Remove it.
Describe what you observe repeat a couple of times and see what happens.
CONCLUSIONS AND QUESTIONS
Answer ach question completely, addressing each part of
- What phases (solid, liquid, gas) are present in the
unlit candle? In the burning candle? Which phase appears to take part in the
- 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
- What two substances are indicated by the cobalt chloride
and limewater tests? Is it possible that other substances are produced when
the candle burns? Explain.
- A source of energy is needed to start the burning of the
candle. What energy source is used? Did the reaction give off or absorb heat?
- How would you explain the copper coil observation?
- Give an example illustrating the difference between
observation and interpretation.