Background
You and your friend's feelings about a movie you've just seen may be very different. You may disagree about wheather you liked the movie, or about the movie's intended meaning. Although yoiu both have observed the same movie, your interpretations of the movie may differ. Distinguishing between observation is a statement of fact, based on what you detected by your senses. An interpretation is your judgement or opinion about what you have observed. A statement such as interpretation to say, without further testing, that the clear and colorless liquid is water.
The purpose of this experiment is to help you distinguish observation from interpretation while examining a chemical reaction. Try to make as many observations of the reaction as possible. Remember that there are two types of observations: A qualitative observation is a general description and does not involve a measurement. "The liquid is hot" is a qualitative observation. "The temperature of the liquid is 95.0 degrees C" is a quantitative observation.
Goals
* Observe several chemical reactions.
* Distinguish between observations and interpretations.
* Classify observations as qualitative or quantitative
Equipment
| safety goggles | 1 glass stirring rod |
| 1 100-mL beaker | 1 plastic spoon |
| 1 thermometer | 1 magnifying glass |
Materials
| copper(II) cloride dihydrate, CuC12 * 2H2O T I | aluminum foil, 8 cm* 8 cm |
Safety
* Note the Safety Symbols used here and in the Procedure
section. Review safety information on pages 7-10.
* Always wear safety goggles when working in the lab.
* Check for odors by waving a hand across the top of
the container, toward your nose, as shown on Figure 2.3.
* Mercury is extremely toxic. If you break a mercury
thermometer, report it immediately to the teacher.
* Copper (II) chloride is an irritant. Avoid skin contact
with this chemical.
Procedure
Copy Table 3,1 into your laboratory notebook. As you perform the experiment, record your observations in this table.
1. Obtain and describe a sample of copper (II) chloride
dihydrate, CuCI2 * 2H2O crystals.
2. Fill the 100-mL beaker about one-fourth full of water.
Without stirring, add 1 level teaspoonful of crystals to th ewater. REcord
your observations of both the crystals and the water.
3. Use the glass stirring rod to stir the mixture until
the crystals are complety dissolved. Record your observations of the solutior.
4. Place the thermometer in the copper (II) chloride
solution and record the temperature. CAUTION: Oberve the mixture
from the side: do not look directly down into the beaker. Place a loosely
crumpled ball of aluminum in the solution and record your observations.
Stir the mixture occasionally and observe for at least 10 minutes. Record
any change in temperature.
5. Follow your teacher's instructions for proper disposal
of the materials.
Data Record
| Table 3.1 Table of Observations | |
| System | Observations |
| dry copper (II) chloride dihydrate | |
| copper (II) chloride in water | |
| stirred solution of copper (II) chloide in water | |
| copper (II) chloride solution plus aluminum foil | |
| initial temperature:
Final temperature: |
Data Analysis
1. Check your observations. Cross out any that are interpretations
rather than observations.
2. List each of your observations inone of the four following
sections. Number your observations consecutively. Circle the number of
any observation that is quantitative.
1. Would you expect your observations or your interpretations to most closely match those of your classmates? Explain.
Extensions
1. What is your interpretion of what
happened in this reaction? Which of the observations led to your hypothesis?
2. Describe any additional experiment you would do to
support your hypothesis.
Data Record