THE SCIENTIFIC METHOD

A WAY TO SOLVE A PROBLEM

What is the Scientific Method?

It is the steps someone takes to identify a question, develop a hypothesis, design and carry out steps or procedures to test the hypothesis, and document observations and findings to share with someone else.

TYPES OF OBSERVATIONS

Quantitative- involves numbers Gravity- 9.8m/sec/sec

Qualitative- physical or chemical qualities

Observations lead to the development of a question.

Direct observations vs. Inference?- LOTS OF INFERENCE IN CHEMISRY!!

Hmmm…what does an atom look like?

The question leads one to…

gather information

(you find s Thomson’s Plum Pudding Model for atomic structure- there are

electrons embedded in a sea of positive charge)

and form a hypothesis

( If Thomson's Plum Pudding model was to be accurate, then big alpha particles will pass through the gold foil with only a few minor deflections because alpha particles are heavy

and the charge in the "plum pudding model" is widely spread.)

The next step scientists take is to create and conduct an experiment to test their hypothesis.

( Rutherford’s Gold Foil Experiment)

Controls- same (atoms Thompson investigated)

Independent variable- what the experimenter manipulates (changes)…

(Alpha particles- large and positive were used and fired through Gold leaf)

Dependent variable-What the experimenter is measuring

(Angle of deflection)

RESULTS, ANALYSIS, and CONCLUSION:

Finally you gather information based on your experiment, analyze the data to determine what your experiment showed you about the phenomena you questioned, and come up with a conclusion based on it. Was your hypothesis correct? Incorrect? Why? What other questions does it leave you with?

The steps of the Scientific Method are:

Observations lead to Questions Background Research-what do we

already know Hypothesis- what do we expect will occur Conduct Experiment- Procedures/Method Collect and Analyze

Results/Table/stats/graphs Conclusion

PERSPECTIVE CHANGES EVERYTHING

IS SCIENCE OBJECTIVE OR SUBJECTIVE???

A lesson in perspective:What we see is dependent on our gaze

What we see is dependent on…

Angle

WHAT WE SEE IS DEPENDENT

…ON HOW CLOSE WE LOOK…

CONCLUSIONS ARE NEVER OBJECTIVE…ALWAYS SUBJECTIVE

SI units: The International System of Units

WHY SI??? To be on the same page…comparing apples to apples (meters to meters, liters to liters)…KING HENRY!

Derived Units Base Units – independent of other units Derived Units – combination of base units

Examples density g/L (grams per liter) volume m x m x m = meters cubed

Reliability of Measurement

ACCURACY – how close a measured value is to the accepted value

PRECISION – how close measurements are to one another - if measurements are precise they show little variation

* Precise measurements may not be accurate

Precision- refers to how close a series of measurements are to one another; precise measurements show little variation over a series of trials but may not be accurate.

LESS THAN .1 IS PRECISE Oscar performs an experiment to determine

the density of an unknown sample of metal. He performs the experiment three times:

19.30g/ml 19.31g/ml 19.30g/ml

Certainty is +/- .01 Are his results precise?

Accuracy and Precision Accuracy – refers to how close a measured value

is to an (theoretical) accepted value. The metal sample was gold( which has a density of

19.32g/ml) Certainty is

+/- .01 Are his results accurate? Need to calculate

percent error. 5% OR LESS IS ACCURATE Oscar finds the volume of a box 2.00cm3 (ml) It is really 3.00ml is it precise? Accurate?

Percent error

NEXT…

PROPERTIES AND CHANGES CLASSIFICATION OF MATTER