The Scientific Method
Purpose:
To observe several chemical phenomena and to formulate hypotheses to explain each
phenomenon.
Background:
The process of science begins with the observation of a natural phenomenon. The scientist then
attempts to understand and explain the phenomenon. A particular approach, called the scientific
method, has proven successful in allowing scientists to achieve an understanding of phenomena
they observe. The purpose of this experiment is to acquaint you with the general features of the
scientific method so that you may apply it in your efforts to understand the chemical phenomena
you will observe in the laboratory this year.
Briefly, the scientific method involves the following steps. First, an observation in made and a
model is developed to explain the observation. The model is called an hypothesis. Experiments
are then designed and carried out to test the hypothesis under controlled conditions.
If the results of the initial experiments support the hypothesis, additional testing must be done to
further support the hypothesis. Only when the results of many, many experiments support the
hypothesis, can it be called a theory. A theory is an hypothesis that has met the test of repeated
experiments.
Frequently, the results of the first few experiments do not completely support the original
hypothesis. In these cases, the hypothesis must be changed, or modified, so that it explains both
the initial observation and the results of the first experiments. The modified hypothesis must
then be tested by additional experiments. When the results of these repeated experiments
indicate that the modified hypothesis is valid and in need of no further modification, it is called a
theory.
In this experiment, you will apply the scientific method to the investigation of chemical
questions. You will make observations of chemical phenomena demonstrated by Mr. Gensits
and then formulate hypotheses to explain the phenomena. As you apply the scientific method in
this experiment, bear in mind that a hypothesis is just an initial step toward understanding. A
hypothesis must be supported by the results of repeated experimentation before it can be said to
explain an observation. Only when a hypothesis has extensive experimental support, can it be
called a theory.
An example of how the scientific method can be applied in the analysis of everyday observations
is provided below:
Observation:
Apples spoil faster when kept on a warm, sunny windowsill, than when
left in a cool, dark cupboard.
Hypothesis:
Apples spoil faster when exposed to light than when left in the dark.
Experiment:
Slice one apple in half and place one half of the apple on the warm,
sunny windowsill. Place the other half of the apple in a bread box on
the same windowsill. The bread box should be closed and made of a
material that will not allow light to reach the apple half within the box.
The temperature within the box should be the same as that outside the
box, i.e., the temperature of the two halves of the apple should be the
same.
Result:
The two apple halves are observed to spoil at the same rate.
Conclusion:
Light has no effect on spoiling rate.
Hypothesis:
(Revised)
Apples spoil faster at higher temperatures than at lower temperatures.
Experiment:
Slice one apple into halves and place one half in an unlit refrigerator.
Place the other half in the closed bread box on the sunny windowsill.
Result:
The apple half in the bread box is observed to spoil faster than the
apple half in the refrigerator.
Conclusion:
Apples spoil faster at higher temperatures than at lower temperatures.
The result of this experiment supports the revised hypothesis. If the results of many more
experiments also support the revised hypothesis, it may be stated as a theory.
Theory:
Apples spoil faster at higher temperatures than at lower temperatures.
Procedure:
As Mr. Gensits performs each of the demonstrations, record your observations on the report sheet
for the experiment. Continue to observe the demonstrations throughout the period. Write an
hypothesis for each demonstration for homework.
Demonstration #1: A piece of clean copper (Cu) wire will be wound around a stirring rod. Silver
nitrate (AgNO3) solution will be poured into a clean large test tube. The copper wire will be
lowered into the silver nitrate solution.
Demonstration #2: A piece of ice (H2O, solid) will be placed on a watch glass.
Demonstration #3: A piece of dry ice (CO2, solid) will be placed on a watch glass.
Demonstration #4: A piece of dry ice will be placed into a water bottle filled with water and the
top of the water bottle will be securely closed.
Demonstration #5: Approximately 900 mL of water will be placed into a 1-L graduated cylinder
and several drops of universal indicator will be added. 75 mL of sodium hydroxide solution
(NaOH) will be added to the water and the mixture will be stirred. Several small pieces of dry
ice will be dropped into this solution.