Introductory Chemistry, 2nd Edition Nivaldo Tro

Chapter Goals:
• Why chemistry?
Introductory Chemistry, 3 rd
Edition
•What do we mean by scientific
method?
•Distinguish between
hypothesis,theory and
scientific laws.
2009, Prentice Hall
What Is Chemistry?
• Chemistry is about relationships
between structure of matter and the
properties of matter (that we
observe).
• It can connect atoms and molecules
to macroscopic events.
(i.e help explain life’s little mysteries!!)
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Why Chemistry?
•Chemistry is a core science! Chemistry and chemicals
affect our daily lives in many different ways !
• helps us understand current events
from a technical perspective
•Whether you want to become a -
biologist,
doctor,
engineer,
or other health science professions
…chemistry will be at the core of your discipline!!
• A process of trying to
understand nature by
observation, and by
experiments to test our
ideas.
• Key characteristics of the
scientific method include
Observation,
Hypotheses,
Experiments, and
formulation of Laws and
Theories.
Tro's "Introductory Chemistry",
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The Scientific Method
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What is “Observation”?
• Also known as Data.
observations can compare a characteristic to a
standard numerical scale.
“A 240-mL serving of soda pop contains 27 g
of sugar.” (this requires experimental
data)
observations can be a simple description
“The soda pop is a liquid with a brown
color and a sweet taste. Bubbles are seen
floating up through it.”
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What we look for in a chemical
Experiment…
Quantitative information:
numerical data (such as
Temperature, melting
points etc..)
Qualitative information:
non-numerical data (such
as color, physical state
such as solid or liquid
etc..)
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What is a “Hypothesis”?
• A tentative explanation of experimental observations.
• Scientists perform more experiments to validate the hypothesis
Note: A test may invalidate the hypothesis too!
Even if a hypothesis is incorrect, it helps scientists approach
A problem in a methodical and thorough manner!
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Law’s
• Scientific laws are based on a vast amount of data, gathered
by many investigators over a long period of time.
• Scientific laws predict future observations but are subject to
further experimentation and revision
• May be stated as a mathematical relationship
Examples:
Law of Conservation of Mass— “In a chemical reaction matter
is neither created nor destroyed.”
Boyles law for gases: V & 1/P
(Volume is inversely proportional to pressure when “number
of moles” and temperature are constant)
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Theories
• In science, a theory has to be supported by data
• A good theory can be proven false, but it is very difficult
to prove a theory to be true.
• One difference between a law and a theory is:
Laws never or rarely change, but theories can change and
new hypothesis emerge as new facts are discovered.
Examples: a) Newtons Law’s of gravity (explains how, but not
why)
b) Atomic Theory
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Practice
1. A hypothesis is
a description of a pattern or relationship in
experimental data
a tentative explanation for a natural
phenomenon
obeyed under any circumstances.
a theory that has been proved
2. The statement, "A chemical reaction never creates products that
weigh more or less than the reactants", is based on three centuries
of experimental observation. The statement is an example of:
a. a theory b. a hypothesis c. a law d. a
data
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