Background for Understanding the Scientific Method through
In this experiment you will use a guided inquiry lab exercise to help you understand the
principles behind the scientific method and the process of using qualitative and quantitative
measurements to make a hypothesis. The five steps of the scientific method can be used in so many
different ways that some people have claimed that there really is no such thing. This is not true. Here
is a brief summary of the steps in this method presented in the context of an example.
Step one: Observation of facts. Imagine there is a lighted candle before you. Imagine that you place
an inverted beaker over the flame and hold it there a moment. (If you do not know what a beaker is,
you may imagine an ordinary drinking glass instead.) At any rate, virtually all people would observe
that the lighted candle is extinguished in a few minutes.
Step two: The Question is now formulated. Why is a lighted candle extinguished when an inverted
beaker is placed over the flame?
Step three: The conception of a hypothesis. We note that the interior of the inverted beaker becomes
lightly coated with soot before the candle is extinguished. Now, black is the "opposite" of light, and
the black soot deposit may have opposed the light from the candle, thus forcing it out of existence.
Step four: The test. Paint the inside of a beaker with black paint; invert it over the lighted candle.
The candle would be extinguished.
Step five: The conclusion: The hypothesis is supported.
Now, before we continue a word of caution. This example illustrates (perhaps crudely) an
important aspect of the scientific method. If a test is performed that supports a hypothesis, it cannot
be assumed that the hypothesis is definitely correct. It can only be said that the hypothesis has not
yet been proven wrong and therefore, perhaps the hypothesis is correct.
Once a hypothesis is tentatively accepted as being correct, it must be subjected to many other
tests. Should it be proved wrong in these later tests, it is discarded or modified and a new hypothesis
is sought. For example we could use a beaker that has been painted white on the inside; or we could
use a beaker painted black but with a few holes in it. Either of these tests would test our hypothesis,
and there are many others that might serve equally well.
Be warned: there are many hypotheses around today which have been supported by
inadequate tests. The difficulty is that no one knows which of these widely accepted "guesses" or
hypotheses are false and which are true. We must await you, or someone like you, to conceive of
new and more conclusive tests to perhaps uncover the inaccuracies of some of our well-thought-of
hypotheses, theories, and laws.
On the bright side, this inability to prove a hypothesis completely correct is actually a great
strength of the scientific method. It encourages scientists to find flaws in a hypothesis that may have
accepted as being correct. That is, scientists are "forced" to reexamine their principles continuously.
In this way we gradually approach closer and closer to the truth, in many cases attaining it, although
we are not always aware of this attainment. This uncertainty in the “right answer” along the way is
one of the most misunderstood aspects of the scientific method and one that often surprises many
students. In a sense, the scientific method uses observations to “build a case” for a hypothesis. This
is done in much the same way that the weight of circumstantial evidence is used in law. The more
circumstantial evidence against the defendant, the more likely that he/she is guilty. However, just as
in law, one simple observation (an alibi) can destroy a hypothesis (a case) and the more observations
(circumstantial evidence) we have, the more difficult it is to discredit the hypothesis.
Enough philosophy (and law), let’s return to that candle. You may have already thought of a
much better hypothesis than the one described earlier. Fore example, the candle burned, producing
carbon dioxide, which was caught in the inverted beaker, thus preventing the entrance of air, which
contains oxygen necessary for burning; therefore, lacking oxygen, the flame went out.
We can challenge this hypothesis easily. We place the candle in an inverted beaker of pure
carbon dioxide and see if it is extinguished sooner. Or, we place the candle in an inverted beaker of
oxygen and see if burns brighter.
Due to the nature of the problems you may be asked or wish to solve, it may not always seem
that you are using the five steps of the scientific method. But by carefully examining your thought
processes, you will find that all types of research are virtually identical to the process just outlined.
To show you how this method compares with the scientific method we have combined the five steps
we described above with the terminology of the "guided inquiry" method presented in your lab
manual in the following experiment.
The Scientific Method in "Guided Inquiry" Terms:
1.Perform the qualitative observations that you are directed to do in the lab manual. This is
equivalent to step 1 of the scientific method.
2.Answer the questions asked by the authors of the experiment regarding these qualitative
observations so that you can develop a hypothesis about the system chosen for you to study.
This is equivalent to steps 2 and 3 above. The questions are written in such a way that they
will provide subtle hints about the hypothesis you are examining. This is one of the “guided”
aspects of this approach.
3.Perform the quantitative observations and do the calculations and graphs to determine the
validity of the hypothesis you made. This is equivalent to step 4 above. Again the method(s)
of quantitative analysis have been carefully chosen by the authors so that they will most
directly support or refute a hypothesis you made. Thus you will not spend time doing
experiments that have no relevance to the hypothesis. As before, you are being “guided” to
use the most efficient procedure to support your hypothesis.
4.Answer questions that will help you make conclusions about the properties of the system by
summarizing or interpreting the relationship between the qualitative and quantitative
observations. This is identical to step 5.
5.Examine alternative relationships as required or optional exercises; You will repeat step 1-5 to
make hypotheses regarding related concepts.
One final note. As you work through this experiment, try to identify which steps of the scientific
method are being used at each point. Also try to figure out how you are being “guided” in your
inquiry in this experiment. By doing this you more clearly understand what is expected from you in
all the other experiments we do in CH 113-114.
Understanding the Scientific Method through Guided Inquiry
Name ______________________________ Lab Partner __________________________
1. Obtain a group of ten pennies from the supply provided so that 2 pennies come from each of the
decades from the 1960s through the 2000s. Examine the pennies and try to list in the space below at
least five similarities and/or differences between the coins.
2. Using the observations you made, what do you think is major effect of age on the mass of a penny
and why? Write your hypothesis below and try to use the observations in step 1 to support it.
3. Go to one of the balances and weigh each of the pennies individually to at least 0.000 grams.
Before placing each of the pennies on the balance pan press the tare button to zero the balance and
reset the number of significant figures to three past the decimal. Record the masses in the table
below along with the date and any other feature that will help you distinguish them from each other.
For example use the mint mark, discolorations, etc.
Date of Penny Mass of Penny (g) Identifying Feature(s)
(1)______________ _____________ _______________________
(2)______________ _____________ _______________________
(3)______________ _____________ _______________________
(4)______________ _____________ _______________________
(5)______________ _____________ _______________________
(6)______________ _____________ _______________________
(7)______________ _____________ _______________________
(8)______________ _____________ _______________________
(9)______________ _____________ _______________________
(10)_____________ _____________ _______________________
4. Try to identify a relationship between the age of the pennies and their mass. Compare it to the
hypothesis you made in step 2. You will find it very helpful to view the data in the table visually by
constructing a graph using the date of the penny and its corresponding mass as the x and y axes.
Remember that the independent variable (x-axis) is the one that you specifically decided to vary in
the experiment. Attach the graph to this report. Describe the relationship(s) you have found and the
appearance of the graph in the space below. Does this match the hypothesis you made in step 2?
Why or why not?
5. What conclusions have you reached concerning the composition of pennies over the this time
span? Also, summarize what you have learned about the scientific method so far (Consult the
background for this experiment for help on this.)
6. Mental Model-Draw a picture(s) that explains at the level of atoms and//or molecules, the pattern
observed in any of the relationships you discovered. Explain how your picture(s) illustrates the
Errors in Quantitative Measurements
Is the conclusion that you reached in step 5 above concerning the effect of age of a penny on its
mass really valid? Or is perhaps due to errors in your ability to make mass measurements or the
inherent inaccuracies in the measuring device you used? How do we determine the effect of errors
on a quantitative experiment? The paragraphs below will summarize some general terminology
about errors and explain how to evaluate them in this experiment.
All quantitative measurements have errors associated with them called systematic, random and
personal errors. Systematic errors occur when the measuring device is not calibrated. Personal errors
occur when the experimenter does not perform the procedure properly. Neither systematic or
personal errors should be tolerated in a chemistry lab since it is assumed that you, a responsible
scientist, will always choose a calibrated measuring device and use it properly. Thus when doing an
“error analysis” you should not try to excuse your results with comments like “perhaps the
thermometer was misread or not calibrated” or “the chemicals were impure”. These types of
comments will be interpreted by the reader (or the instructor), that you are unable to perform the
procedure properly. If there was an unforeseen event that results in personal or systematic errors you
should try as best you can to interpret the data you have collected and determine the magnitude of
the errors involved. An error (or disaster), carefully explained and accounted for, will restore the
reader’s (or the instructors) confidence in your ability.
The types of errors you should consider as part of even the best of experiments are called random
errors. These are due to the inherent precision of the measuring device. Some devices even have
more than one level of precision or uncertainty. For example, a 10 mL graduated cylinder could be
read, with practice, as accurately as 0.1 mL. However, there are times when you will only use this
device to estimate the volume to the nearest 1 mL. In these cases the accuracy of the measurement
depends on your needs. For example, when writing down the volume it does make a difference
whether you record it as 1.0 mL or 1 mL. You must always be aware of the precision of the
measurements that you make and how they are recorded.
There are a number of ways that the precision of a series of measurements can be determined.
The first method can be used when multiple measurement of the same value are performed. The
range of measured values can be calculated and reported. The second method uses the precision of
each measuring device and its inherent uncertainty to determine the number of significant figures.
The inherent uncertainty is usually provided by the manufacturer of the device or the number of
significant figures on the display. The rules for manipulating significant figures should already be
familiar to you from other science courses or you can use the ones that you learn in lecture.
7. How similar are the mass measurements for each type of penny? Examine the masses and
determine the range of each set of different values by taking the largest mass measurement in the set
and subtracting the smallest in the set. This difference is one way to determine the precision of the
measurements. What conclusion can you draw about the precision of the mass measurements and the
concept of random errors? Would you describe the precision of your measurements as very good,
good or poor? What criteria did you use to decide if it was very good, good or poor?
8. How many significant figures did you get from the balance display? Are the differences in the
mass measurements of the pennies as calculated in step 7, for each type of penny, similar to the
precision of the smallest significant digit from the balance? Would you describe the precision of
your measurements as very good, good or poor? What criteria did you use to decide if it was very
good, good or poor?
Precision versus Accuracy
One last point concerning error analysis. Although it may not seem like it at first, precision is not
the same as accuracy. Accuracy is how close the measured or calculated value comes to some
accepted value. To determine the accuracy of your experimental mass values the “percent error” is
calculated using the equation:
| accepted value - experimental value |
% error = ------------------------------------------------------------ x 100
9. Calculate the percent error using your average for each type of penny as the accepted value. The
calculation of percent error requires an accepted or literature value. Now calculate the percent error
using accepted mass of a penny at the US Mint’s web site:
10. Would you describe the accuracy of your measurements as very good, good or poor? What
criteria did you use to decide if it was very good, good or poor? Does the calculated percent errors
change the conclusions you made in any of the earlier parts of this exercise? Explain why or why