The Scientific Method
Purpose:
To observe several chemical phenomena and to formulate hypotheses to explain each
phenomenon.
Background:
Science is devoted to formulating and testing naturalistic explanations for natural phenomena. It
is a process for systematically collecting and recording data about the physical world, then
categorizing and studying the collected data in an effort to infer the principles of nature that best
explain the observed phenomena.
The scientific community has developed a vocabulary to describe the various aspects of the
scientist’s work. Although individual scientists are not always careful in their use of that
vocabulary, a rigorous set of definitions can help to prevent confusion about what a scientific
fact, hypothesis, or theory is.
The grist for the mill of scientific inquiry is an ever-increasing body of observations that give
information about underlying “facts.” Facts are the properties of natural phenomena. The
scientific method involves the rigorous, methodical testing of principles that might present a
naturalistic explanation for those facts. To be a legitimate scientific “hypothesis,” an
explanatory principle must be consistent with prior and present observations and must remain
subject to continued testing against future observations.
The process of continuous testing leads scientists to accord a special dignity to those hypotheses
that accumulate substantial observational or experimental support. Such hypotheses become
known as scientific “theories.” If a theory successfully explains a large and diverse body of
facts, it is an especially “robust” theory. If it consistently predicts new phenomena that are
subsequently observed, it is an especially “reliable” theory. Even the most robust and reliable
theory, however, is tentative. A scientific theory is forever subject to re-examination and – as in
the case of Ptolemaic astronomy – may be rejected after centuries of viability.
Every scientific discipline embraces a body of facts and one or more theories to explain them.
Scientific facts and theories are not interchangeable: An explanatory principle is not to be
confused with the data it seeks to explain. This relationship between scientific theory and fact
permeates all scientific disciplines; it unifies the enterprise of all scientists, from astronomers to
chemists.1
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 a hypothesis. Experiments
1 The above discussion of scientific method and theory was taken from the Edwards v.
Aguillard: Amicus Curiae Brief of 72 Nobel Laureates in 1986.
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 a 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.
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 a
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.