Chemistry Chapter 2 The Scientific Method

Goals: Describe the purpose of the scientific method Distinguish between qualitative and quantitative observations Be able to define hypothesis, theory, scientific law, model

Scientific Method Logical approach to solving a problem A series of repeatable steps Steps do not always go in the same order ▫Some steps may be repeated

Steps! First, one must define the problem to be studied ▫Problem identified by observation  Observation: using senses to collect information  May be quantitative and/or qualitative ▫Problem must be a limited system  System: specific part of the universe being studied

Steps! Next, one states the hypothesis ▫Hypothesis is key to science  Must be testable  Must attempt to explain observations  Basis for predicting results and carrying out experiments  Often stated as “if-then” statements

Steps! Testing the hypothesis ▫Test may be experiment or observations with control  Observations: quantitative and/or qualitative  Control: part of the experimental group where no experimental factor is used  Designed to allow comparison of experimental group ▫Test must be repeatable ▫Data are collected during testing  Variables measured:  Independent variable  Dependent variable

Steps! Evaluation of data and drawing conclusions ▫Data collected during experiment or observations is evaluated  Does the data support the hypothesis?  Does the data disprove the hypothesis?

Steps! Reporting ▫Reporting is essential in science ▫Science is peer-reviewed ▫Work must be repeatable and retestable

Results of Scientific Method Model ▫Explanation of how phenomena occur ▫Used to explain observations Theory ▫One or several hypothesis tested often and not disproved ▫Explains and predicts observations Scientific Law ▫General statement of relationships observed in science ▫Does not explain ▫Based on many hypotheses that have been rigorously tested

Metric System  Some standard units: (others will be added later)  Time:  Second (1/86400 of mean solar day)  Length  Meter (10 -7 distance from N pole to equator)  Mass  Kilogram (based on standard kept in France)  Fluid volume  Liter (volume of 1 dm 3 of water) Derived units: Combine measurements of two or more standard units Example: density = mass/volume

Prefixes Standard metric units are divided or multiplied by 10s to get larger or smaller units These units are named using prefixes added to the standard unit name We will be able to convert between units easily simply by moving the decimal point ▫That’s why the metric system is so cool!

Common Metric Prefixes: Larger  Deka (da)  10 x (10 1 )  Hecto (h)  100 x (10 2 )  Kilo (k)  1000 x (10 3 )  Mega (M)  x (10 6 )  Giga (G)  x (10 9 )

Common Metric Prefixes: Smaller  Deci (d)  1/10 (10 -1 )  Centi ( c )  1/100 (10 -2 )  Milli (m)  1/1000 (10 -3 )  Micro ( μ )  1/ (10 -6 )  Nano (n)  1/ (10 -9 )  Pico (p)  1/ ( )

Mr. Boal’s Handy-Dandy Conversion Line We can EASILY convert from one unit to another That’s the beauty of the metric system! For example ▫How many mm are there in 12 m? ▫What is 500 nanometers equivalent to in meters?

Sample Problems: How many g are there in 882 µg? How many mL are there in L?