Scientific Method - Ohio State University

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Transcript Scientific Method - Ohio State University

Chemistry 121
Dr. Patrick Woodward
Office  3109 Newman and Wolfrom Lab
Office Hours  2:30-3:30 M, T, W, R
E-mail  [email protected]
Phone  688-8274
Web Site 
Chemistry 121
Required Materials
Text  “Chemistry, The Central Science” by Brown,
Lemay and Bursten 9th Edition
Lab Manual  “General Chemistry Laboratory
Experiments, Volume 1” by Casey & Tatz
Lab Notebook  “Student Laboratory Notebook”
Calculator  TI-30, Sharp EL-509, Sharp EL-531,
Casio FX-250
Grading Scheme
Midterm 1 (Tues, Feb 3rd)
Midterm 2 (Tues, Feb 24th)
Final Exam (Tues, Mar 16th)
Laboratory (10 labs)
Quizzes (6 Quizzes, drop the lowest)
Opportunities to do problems
 Take home quizzes
 Recitation Exercises
 Homework Problems (at the end of the chapter)
 Web Material (Old exams, sample quizzes, CD
Top 5 Myths about Chem 121
5. This class is a weed out class.
For example consider the final grade distribution from
Autumn 2002 (beginning with ~300 students):
21 Dropped
20 Failed
29 D/D+
126 C-/C/C+
59 B-/B/B+
46 A-/A
Top 5 Myths about Chem 121
4. It’s OK to blow off lab, because it’s only 20% of your
If you don’t get 50% in lab, you will be given a failing
grade. Extra time will not be given to make up missed
Top 5 Myths about Chem 121
3. The curve will save me.
If you get below 600 points (60%) the best grade you can
hope for is C-, and your likely to get a D or D+.
If you get below 500 points (50%) you’re almost certain to
fail the class.
Top 5 Myths about Chem 121
2. There are so many students that office hours will be
very crowded, plus professors don’t want to be
Office hours are usually only crowded before the
exams. I set aside time to see you during office hours
so it’s boring when no one comes. I’m also happy to
make appointments for other times if you have
conflicts with my office hours.
Top 5 Myths about Chem 121
1. Knowledge of chemistry will make you more attractive
to the opposite sex and enhance your love life.
Unfortunately based on personal experience I see no
evidence for this kind of cause and effect relationship.
Scientific Method
Keep in mind though that generally hypotheses and even
theories are based on an incomplete set of experiments,
so that later experiments or advances may provide
further information that shows the theory or
hypothesis to be incorrect.
Classification & Properties of Matter
Matter – Anything that has mass and occupies space.
Atom – The smallest stable building block of matter. Made up of
protons, neutrons & electrons.
Molecule – Groups of atoms held together with a specific
connectivity and shape.
Composition tells us the types of atoms that are present in a
compound and the ratio of these atoms (for example H2O, C2H6O,
Structure tells us which atoms are connected (bonded) to each
other, how far apart they are, and the shape of the molecule.
Elements, Compounds & Mixtures
Pure Substance  Matter that has a fixed composition and
distinct properties. All substances are either elements or
Elements  All atoms are the same, i.e. Oxygen (O2), Gold (Au),
Silicon (Si) and Diamond (C).
You should memorize the elemental symbols in Table 1.2
Compounds  Contains more than one type of atom, but all
molecules (or repeat units) are the same, i.e. Water (H2O), Ethanol
(C2H6O), Quartz (SiO2), Sodium Chloride (NaCl). All compounds
follow the law of constant composition.
Mixture  Have variable composition and can be separated into
component parts by physical methods. Mixtures contain more than
one kind of molecule, and their properties depend on the relative
amount of each component present in the mixture.
Periodic Table
Homogeneous & Heterogeneous Mixtures
Homogeneous Mixture  Composition and properties are
uniform. Sometimes called a solution.
Air – principle components include O2, N2 & CO2
Vodka – principle components are ethanol and water
Brass – solid solution of Cu and Zn
Ruby – solid solution of Al2O3 and Cr2O3
Heterogeneous Mixture  Composition and properties are
Chocolate Chip Cookie – Chocolate, Dough, etc.
Concrete – Cement, Rocks, etc.
Vomit – Depends upon previous intake of food and drink
Chemical and Physical Properties
Physical Properties  The identifying characteristics of
matter. Some properties can be readily measured with our senses,
such as odor and color, instruments are needed to measure other
properties, such as electrical resistivity, compressibility, hardness,
melting point, etc.
Chemical Properties  Describe the reactivity of a substance
toward other substances. Examples include:
Ethanol burns in air (reacts with oxygen in the air)
Sodium reacts vigorously with water,
Corrosion of metal parts (rust),
Trinitrotoluene (TNT) is explosive,
Lysergic acid diethylamide (LSD) is a hallucinogenic drug.
Stoichiometry = C2H6O
Melting Point = -115 ºC
Boiling Point = 78 ºC
Density = 0.79 g/cm3
Chemical Prop. = Intoxicating
Dimethyl Ether
Stoichiometry = C2H6O
Melting Point = -140 ºC
Boiling Point = -24 ºC
Density = Gas
Chemical Prop. = Intermediate
Ethylene Glycol
Stoichiometry = C2H6O2
Melting Point = -16 ºC
Boiling Point = 197 ºC
Density = 1.11 g/cm3
Chemical Prop. = Toxic
SI (Metric) Units
Metric Prefixes
You will be expected to know these prefixes from memory.
Significant Figures
1. Non-zero numbers are always significant.
2. Zeros between non-zero numbers are always significant.
3. Zeros before the first non-zero digit are not
significant. (Example: 0.0003 has one significant
4. Zeros at the end of the number after a decimal place
are significant.
5. Zeros at the end of a number before a decimal place are
ambiguous (e.g. 10,300 g).
Significant Figures &
Addition and Subtraction
Line up the numbers at the decimal point and the answer
cannot have more decimal places than the measurement
with the fewest number of decimal places.
Multiplication and Division
The answer cannot have more significant figures than
the measurement with the fewest number of significant
Precision and Accuracy
Units of Volume
1 m3  (1003 cm3)/(1 m3) = 1,000,000 cm3
1,000,000 cm3 = 1  106 cm3
Periodic Table
Chemical Reactivity
2H2(g) + O2(g)  2H2O(g)