Observing a Chemical Reaction
Introduction
As with all experimental sciences, the science of chemistry is based upon observation. In
this experiment, you will observe a chemical reaction. It is unlikely that you will understand
all that is happening, but, at this time, it is not necessary that you do. Rather, the purpose
of this experiment is to give you practice in distinguishing observation from interpretation.
An observation is a statement of fact, based on sensory data. An interpretation is a
judgment or opinion about what is observed. A statement such as “the liquid is clear and
colorless” is an observation. It would be an interpretation to say, without further testing,
that the clear and colorless liquid is water.
As you observe the reaction in this experiment, try to make as many observations as
possible. Be aware that a quantitative observation is an observation that involves a
measurement. A qualitative observation is a general description and does not involve a
measurement. “The liquid is clear” is a qualitative observation. “The temperature of the
liquid is 95C is a quantitative observation.
Objectives
1. To make as many observations as possible of a chemical reaction.
2. To learn to distinguish between observations and interpretations.
3. To learn to distinguish between qualitative and quantitative observations
Procedure
Safety Precautions: Wear Safety Goggles at all times.
Copper(II) chloride is a skin irritant.
As you perform the experiment, record your observations in your lab notebook.
1. Measure out approximately a 4 cm x 4 cm piece of aluminum foil and place to the
side. Record observations.
2. Carefully place a small spoonful of copper (II) chloride in a watch glass. Record
observations.
3. Fill a 100 ml beaker to about one-fourth full of tap water. Record observations.
4. Add the crystals to the water. Gently stir the copper (II) chloride and water
and record your observations.
5. Place the beaker on the base of a ring stand. Attach a thermometer to the ring
stand using a clamp and lower the thermometer into in the copper (II) chloride
solution and note the temperature.
6. Loosely crumple the aluminum foil into a ball.
7. Place the aluminum ball in the solution, using a stirring rod to press down on the
aluminum until a reaction starts. Measure and record the highest temperature
and record your observations of the mixture; CAUTION: Observe the mixture
from the side. Do not look directly down into the beaker.
8. Continue to observe the mixture for at least 10 minutes and note any change in
temperature. Does stirring the mixture have any effect on the reaction?
9. When the reaction is complete, empty the contents of the beaker into the
chemical waste container provided by your teacher.
10. Wash and dry the equipment that you used. Wash your hands thoroughly before
leaving the classroom.
Observations
System
Aluminum foil
(Al)
Copper (II) chloride
(CuCl2)
Water
(H2O)
Copper (II) chloride
and water after
stirring
(CuCl2 & H2O)
Copper(II) chloride,
water and aluminum
foil Immediately
(CuCl2 , Al & H2O)
Copper(II) chloride,
water and aluminum
foil
After Reacting
(CuCl2 , Al & H2O)
Observations
Temperature (C)
Analysis of Observations
1.
What is the difference between an observation and an interpretation. Check
your observations. Eliminate any that are interpretations rather than
observations.
2. Circle any observation that is quantitative data.
3. A thermometer placed in the beaker can be used to determine whether the
reaction released heat or absorbed heat?
 Endothermic Reactions absorb heat and a solution will decrease in

temperature.
Exothermic Reactions release heat and a solution will increase in
temperature.
Was the reaction exothermic or endothermic? Explain why (how could you tell).