Chemistry Chapter 2The 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 dm3 of water)

Derived units:Combine measurements of two or more standard unitsExample: 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 (101) Hecto (h)

100 x (102) Kilo (k)

1000 x (103) Mega (M)

1 000 000 x (106) Giga (G)

1 000 000 000 x (109)

Common Metric Prefixes: Smaller Deci (d)

1/10 (10-1) Centi ( c )

1/100 (10-2) Milli (m)

1/1000 (10-3) Micro (μ )

1/1 000 000 (10-6) Nano (n)

1/1 000 000 000 (10-9) Pico (p)

1/1 000 000 000 000 (10-12)

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 6.023 L?