Scientific Method

Chapter 1

What is Science?

A Way to Know About Things

What Are Terms Associated with Science?

• Observations

• Objectivity

Factors that AffectObservations and Objectivity

1. Assumptions2. Time3. Previous Experience

Scientific Method

Form a Conclusion

Orange - wrong

Potato - correct

Observation

A paper bag is on a counter - what is in it?

Proposing a Hypothesis

Inside is a sandwich

Test the Hypothesis

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?

• 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.

– Observation: if he burned the phosphorous in a closed container, it weighed the same before and after.

– 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 - SpecialistsPrimary source journals that describe research results.

Examples:Analytical ChemistryJournal of Organic ChemistryElectrochemical ACTA

Level 2 – Some background in scienceGeneral science magazines that contain articles often written by specialists

Scientific AmericanPopular MechanicsScience NewsDiscover

Level 3 – General publicMagazines or newspapers that have some science writers on their staff

National GeographicThe New York TimesThe Los Angeles Times

Level 4 – General publicTV and local newspapers. Information is severely diluted.

KRON 4 newsThe Oakland TribuneThe Santa Clarawww?

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

• 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 moond) You were Abraham Lincoln in a past life.

Solving Problems Using a Scientific Approach

1. Define the Problem• Design Experiments• Gather Information

• Facts• Observations

2. Propose Solutions• Organize Information and look for Patterns• Hypotheses

3. Evaluate your Proposed Solutions• Plan future work

• Test your patterns by using them to predict what will happen

• Check for reproducibility

4. Communication your findings• Publish your results

• What is the purpose of this experiment?

• What does the chemist need to observe/measure?

A chemist in an imaginary universe does an experiment that attempts to correlate the size of an atom with its chemical reactivity.

Size of Atom

Chemical Reactivity

Small Low

Medium Intermediate

Large High

• Can you formulate a law from this data?

• Can you propose a theory to explain the law?

ACB 1

Observations: when A, B or C reacts with 1…