Ms. Rozema’s Chemistry Class (Fall 2010)
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It is a method, that is used to find answers to
questions about the world around us.

Only One Method?
 No
 Some versions have more steps.
 They all begin with the identification of a problem or
question to be answered.
 Our problem provides an experimental method

Hypothesis:
 Testable Statement based on observations

Data:
 Information gathered during an experiment

Control: An entire experimental set-up which
remains “neutral”, used for comparison.

Constant: Common/Similar parts to different
experimental set-ups.
Variable: Something that changes during the
experiment.
Experimental / Independent Variable: The variable
you set-up and test.


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Observational / Dependent Variable: The variable
that you observe (the result of your test).

“To Support”: Providing lots of detailed data to
convince a reader of your conclusion.

Pattern: A general observation which occurs
multiple times.
Conclusion: A statement which defends the
accuracy of your hypothesis using data collected.

Problem / Question
Predictions & Hypothesis
Procedure
Experiment
Data Analysis
New Procedure
Conclusion

Observations use your 5 Senses to take note:
 An observation is taking note of what actually
happened!
 Observations are absolutely necessary during data
collection!

Inferences use your prior knowledge to make
predictions/assumptions…
 An inference is taking note of what you thought
happened or why you think it happened!
 Inferences are NEVER to be used during data
collection, and only when writing your
predictions/hypothesis!
Problem / Question

Visual Descriptions (What did you see?):
 Color
 Shape
 Texture / Print / Pattern
 Bubbles, Steam, Condensation
 Size / Quantity

Auditory Descriptions (What did you hear?):


Fizzing
Popping

Olfactory Descriptions (What did you smell?):
 Sweet, Sour
 Burnt
 Compare to known smells

Touch Descriptions (What did you feel?):




Cold, Hot
Soft, Smooth
Rough, Sharp
Measurements:
 Mass (grams), Volume (mL)
 Height / Length (cm)
#1)
What observations
can you make? (List
in your table!)
What inferences
could you make?
(List in your table!)
#2)
What observations
can you make? (List
in your table!)
What inferences
could you make?
(List in your table!)
#3) You are conducting an experiment to determine if increased
ultraviolet radiation from the decrease in the ozone layer is killing off
frog tadpoles. After examining all of the data available in the library,
you decide to go with a hypothesis that increased ultraviolet radiation
from the sun is killing off the tadpoles. You design an experiment with a
control and an experimental group. Your control group (group 1)
involves 100 tadpoles in a five gallon container of water, that is covered
by glass (knowing that the glass will filter out the ultraviolet radiation).
The experimental group (group 2) will be set up exactly like group 1,
except that instead of being covered with glass, it is covered with an
acrylic plexiglass, which will not filter out the U.V. radiation. You then
place the groups outside for a period of a month, and observe the
results.
Results
Group 1
Group 2
Initial Number of Tadpoles
100
100
Ending Number of Tadpoles
96
96
a. What is the experimental variable and what is the dependent variable?
- Experimental Variable = UV Radiation present
- Dependent Variable = Ending Number of Tadpoles
a. Does the information from this experiment support the hypothesis? No
b. If no, then what might be causing the decrease in frog populations?
- Changes to temperature, oxygen, food availability, mating success
c. Which is the control group, and which is the experimental group?
- Control Group = Group 1 = Tadpoles without UV Radiation
- Experimental Group = Group 2 = Tadpoles with UV Radiation
d. What is the difference between the 2 groups? Should they be different in any
other way?
UV Radiation…. No, too many variables makes it hard to conclude!
#4)
Niko Tinbergen (1907-1988) was a Swedish Ethologist (animal behaviorist) famous
for studying animals in their native habitats. One of his classic experiments involved a bird
called the black-headed gull (Larus ridibundus). Black-headed gulls build nests of twigs on the
ground and lay light brown eggs that are covered with dark brown spots. However, the inside of
the egg is white in color. Tinbergen noticed that adult gulls pick up the eggshells shortly after a
chick has hatched, and fly them to a location far from the nest, where they are left. Since this
behavior required expending energy and time that could have been spent feeding and
protecting the chicks, Tinbergen wanted to know why the birds did this.
Problem: Why do black-headed gulls remove eggshells from the nest?
Hypothesis: The white interior of the shell is not camouflaged and attracts predators to the
nest. Therefore, the gulls remove the shells to decrease predation.
Test: Tinbergen and his co-workers collected gull eggs and painted 69 of them white and left
68 of them with their natural color. (Statistically, these numbers are close enough to be
considered equal.) The researchers then scattered the eggs next to a gull breeding area and
observed from a nearby blind. Predation rates were recorded for white versus natural colored
eggs.
Data
White Eggs
Natural Eggs
Original
Eggs Taken by
Number of Eggs
Predators
69
43
68
13
Eggs Not Taken
26
55
a. Do the results of this experiment support the hypothesis? Why, Why not?
- Yes, the results do support his hypothesis.
b. Are you 100% sure (without a doubt) that your hypothesis is correct?
- No. There may be other factors playing in, aside from camouflaging. To make sure I would
request that this test be completed many more times, in different locations.
- Also—His starting number is not the same, and while not a huge difference, still odd.
c. If you were working with Tinbergen, what would you suggest be done next?
- I would suggest painting the eggs different colors (white, bright yellow, bright red, etc.) to test
the camouflage hypothesis.
- I would also suggest that we re-complete the same experiment multiple times and collect data.
- I would also suggest starting with the same number of eggs!
d. Identify the experimental and dependent variables.
- Experimental Variable = Egg Color
- Dependent Variable = Number of Eggs Taken by Predators