The Scientific MethodSignificant Figures

The Scientific Method Based on Observations and Data

Observations – hopefully quantitative measurements that appear to relate two or more concepts: heating time and temperature, pond depth and sound of splash, number of “skips” compared to “flatness” of rock, etc.

Law – Statement or equation showing the relationship between properties or concepts

Hypothesis – a proposal to explain the relationship between one concept or property on another

Experiment – set of controlled steps that are meant to determine whether or not the hypothesis is correct. Control for other variables is important

More Experiments/Evaluation of Hypothesis – Further tests to see if predicted behavior holds

Theory – Hypothesis that has held up after many experiments and tests

The Scientific Method

The experiment must control for the variables that might impact the observations beside the one(s) you are trying to test.

An hypothesis is often changed as new kinds of data or methods of measurement become available.

Once tested, an hypothesis becomes a Theory. Theories are used to explain the behavior of things until different or better ways of making observations become available, and remain valid unless the new observations provide conflicting predictions.

Scientific Law

Scientific Laws, like the Law of Gravity or Newton’s Laws of Motion, are rare.

Scientific Laws provide a relationship (usually mathematical) that is widely used and accepted, but do not usually provide an explanation of the observed effect.

Accuracy vs PrecisionAccurate and Precise Precise

Accurate Neither Accurate nor Precise

Systematic error

Random Error

Accuracy vs Precision

Significant Figures

Used to indicate the degree to which a number is “known”

If you weigh 150 pounds, does that mean you weigh 150 + 0.1 , 150 + 1, or 150 + 10?

Since 1 kg = 2.205 lb, how many kg do you weigh?

150 lb x (1 kg/2.205 lb) = 68.0272 kg

If you are 5 ft, 8 in tall, what is your average density?

Determining Significant Figures

Rules for Using Significant Figures

Rules for Using Significant Figures

Using Significant Figures

Chemical Conversions

Unit conversions and dimensional analysis are very important parts of calculations in chemistry.

A conversion factor is an equation that relates two different units to one another.

Simple: 100 cm = 1 mMore difficult: 1 in = 2.54 cm

Simple conversion

SI Base Units

Decimal Conversions

English to SI Conversions

Temperature Conversion

Celsius/Fahrenheit ConversionRelation between degrees: 1 oC = 1.8 oF

T(oF) = 1.8 x T(oC) + 32

Celsius/Kelvin ConversionRelation between degrees: 1 oC = 1 K

T(K) = T(oC) + 273.15

Problems

1.15, 1.19, 1.22, 1.43, 1.49, 1.51, 1.53, 1.57, 1.60, 1.62, 1.67, 1.70, 1.72, 1.74, 1.75, 1.87