Scientific Method
Chapter 1
What is Science?
A Way to Know About Things
What Are Terms Associated with Science?
• Observations
• Objectivity
Factors that Affect
Observations and Objectivity
1. Assumptions
2. Time
3. Previous Experience
Scientific Method
Observation
A paper bag is on a counter
- what is in it?
Form a Conclusion
Orange - wrong
Potato - correct
Proposing a
Hypothesis
Test the
Hypothesis
Inside is a sandwich
Smell, shake, feel
Revise the Hypothesis
Tangerine, candle
What is science?
• Body of knowledge about nature
• Product of observations, common
sense, rational thinking and
(sometimes) brilliant insights
• A methodology of exploring nature
and discovering the order within it.
• Tool for solving problems
Why study science?
•
•
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Basic & Applied Research
Health
Environment
Technology-based economy
Ethical questions
• More than 70% of all legislation before Congress
addresses science-related questions and issues
Chemistry – The Central Science
• Is the study of matter and transformations of matter
What is Chemistry?
• Chemists want to understand how
the things work.
– Why are leaves green?
– What happens when
water boils?
– Why does soda fizz?
• Applications in
– New Materials
– New Pharmaceuticals
– New Energy Sources
– Food Supplies
Chemistry tries to understand the macroscopic world by
examining the behavior of atoms and molecules
Chemistry is the science that investigates
the molecular reasons for the processes
occurring in our macroscopic world.
• What happens when sugar is added to hot tea?
How do chemists come up
with these explanations
to these processes?
Scientific method
Observation
• A way of acquiring information about nature
• Some observations are simple descriptions about
the characteristics or behavior of nature
– “The soda pop is a liquid with a brown color
and a sweet taste. Bubbles are seen floating
up through it.”
• Some observations compare a characteristic to a
standard numerical scale
– “A 240 mL serving of soda pop contains 27
grams of sugar.”
Hypothesis
• A tentative interpretation or
explanation of your observations
– “the sweet taste of soda pop is
due to the presence of sugar”
• A good hypothesis is one that can
be tested to be proved wrong!
– Falsifiable
– One test may invalidate your
hypothesis
Experiments
• Tests of hypotheses, laws or theories
• Can you think of a way to test whether the sweet taste of soda pop
is due to the presence of sugar?
• Results either Validate (confirm) or Invalidate (deny) your ideas
– Invalidate = Discard or Modify
• Many times experiments invalidate only
parts of the hypothesis or theory, in which
case the idea is modified
– Validate ≠ Proof your idea will always hold
McClintock and Baker notice
something unusual in the Antarctic
• Observations:
– Amphipods carry sea butterflies on their
backs.
– Amphipods who lost their sea butterfly
would quickly find another sea butterfly.
– Amphipods carrying sea butterflies move
much slower than amphipods without sea
butterflies
• Question:
– If sea butterflies slow down the amphipods
thus making them more vulnerable to
predators, why do amphipods carry sea
butterflies?
McClintock and Baker’s Hypothesis
• Hypothesis
– Amphipods carry sea butterflies
because the sea butterflies
produce a chemical that deters
the predator of amphipod.
• Experiment
– Place predator fish in tanks with
a) sea butterflies
b) amphipods and
c) amphipods & sea butterflies
• Could something besides a chemical
cause the predator fish to spit out
the sea butterflies?
A better experiment
•
Control Tests: Ideally designed so
that only one variable changes
•
Experiment:
– Predator fish placed in tanks
with a) control pellets (fish
meal) and b) pellets containing
sea butterfly extract
Scientists confirm experimental
results by repeated testing
Results of a scientific experiment
are considered valid only if they
can be reproduced by other
scientists
Molecule found to deter predator fish
Scientific Method
1. Observe…using your naked eye or instrument…
• People noticed when logs were burned, they lost
weight…
2. Propose an explanation or hypothesis…
• People reasoned that the logs must be losing
something and named that substance phlogiston.
Scientific Method
3. Be skeptical – test that hypothesis!
• A French scientist, Lavoisier decided to test the
explanation. If substances lose phlogiston when
they’re burned, if I burn something else, i.e.
phosphorous, they will lose weight.
4. Test the hypothesis with an experiment.
• Lavoisier found that phosphorous gained weight
when burned.
Scientific Method
5. Revise the hypothesis and test again.
–
Lavoisier ran more experiments.
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Observation: if he burned the phosphorous in a closed container,
it weighed the same before and after.
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Observation: if he burned the log in a closed container, it also
weighed the same before and after.
What’s his new hypothesis?
Scientific Method
• Make Predictions
• Working towards an explanation
Law – A summary of observations
• A law combines all past observations into one general
statement
– Law of Conservation of Mass – “In a chemical reaction
matter is neither created nor destroyed.”
• Law is not an explanation.
• Allows you to predict future observations
– So you can test the Law with experiments
Working towards an explanation…
• More experiments…
– with phosphorous and
with mercury…
• Observations:
– Balloon deflated
– the ash weighed more
than the phosphorous or
mercury.
Theory – an explanation
of molecular behavior
• Can be used to predict future observations
– So they can be tested by experiments
• Lavoisier’s theory:
– Phosphorous is combining with the oxygen in the air.
– Mercury is combining with the oxygen in the air.
• How did he know there was oxygen in the air?
– Communication – he read the reports of Priestly and Scheele
who discovered oxygen.
Research involves communication
• When scientists have ideas they look to the literature to see if
anyone else had the same idea or similar ideas.
• Publishing results allows other scientists to confirm the
reproducibility of the results
• And occasionally, people arrive at the same idea independently…
– that’s why scientists write down their observations in pen and
date their lab work.
• There can be disputes about who came up with an idea 1st. The
decision on who gets credit or the profit from the idea is sometimes
made by looking at the lab notes as documentation of the idea.
Where can you find chemical information? And how
accurate will it be?
Level 1 - Specialists
Primary source journals that describe
research results.
Examples:
Analytical Chemistry
Journal of Organic Chemistry
Electrochemical ACTA
Level 2 – Some background in science Scientific American
General science magazines that contain
Popular Mechanics
articles often written by specialists
Science News
Discover
Level 3 – General public
Magazines or newspapers that have some
science writers on their staff
National Geographic
The New York Times
The Los Angeles Times
Level 4 – General public
TV and local newspapers. Information is
severely diluted.
KRON 4 news
The Oakland Tribune
The Santa Clara
www?
Science has limitations
• No experiment can ever prove definitely that a scientific hypothesis
is correct.
• We gain more and more confidence in a hypothesis (theory) as it
continues to be supported by the results of many different
experiments conducted by many different investigators.
• If an experimental result contradicts the hypothesis and the result is
reproducible, the hypothesis must be discarded or revised.
Science only deals with hypotheses
that are testable
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Science is restricted to the natural world.
Cannot answer philosophical or religious questions, such “What is
the purpose of life”
“What is the nature of the human spirit?”
•
Which statement is a scientific hypothesis?
a) The moon is made of Swiss cheese.
b) Human consciousness arises from an essence that is
undetectable.
c) Tides are caused by the moon
d) You were Abraham Lincoln in a past life.
Solving Problems Using a Scientific Approach
1.
Define the Problem
• Design Experiments
• Gather Information
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2.
3.
Propose Solutions
• Organize Information and look for Patterns
• Hypotheses
Evaluate your Proposed Solutions
• Plan future work
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4.
Facts
Observations
Test your patterns by using them to predict what will happen
Check for reproducibility
Communication your findings
• Publish your results
A chemist in an imaginary universe does an
experiment that attempts to correlate the
size of an atom with its chemical reactivity.
• What is the purpose of this experiment?
• What does the chemist need to observe/measure?
Observations: when A, B or C reacts with 1…
Size of Atom
Chemical
Reactivity
Small
Low
Medium
Intermediate
Large
High
A
B
C
• Can you formulate a law
from this data?
• Can you propose a theory
to explain the law?
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