Chapter 1: Chemical Foundations
I. An Overview of Chemistry
A. Chemistry is involved in everything around you
1. Chemical energy is converted to electrical energy in batteries
2. Computers and projectors utilize hundreds of “chemicals” to function
3. Chemical reactions allow your brain to understand this sentence
B. Chemistry is the study of matter
1. The properties of matter depend on the identity of the tiny atoms that make
it up and how they interact with each other
2. Understanding how microscopic atoms translate into macroscopic
properties is a major challenge of chemistry
C. Some Core Ideas of Chemistry
1. The diversity of substances result from about 100 types of atoms
2. These atoms can combine to form multi-atom molecules
3. Reorganizing the atoms’ attachments changes the type of matter
4. Example: Hydrogen, Oxygen, and Water
5. The study of the types of atoms and their reactions is our task
II.
The Scientific Method
A.
There is no single method for doing science
1. “The” scientific process = Observing, Collecting Data, Hypothesizing,
Experimenting, Concluding (Karl Pearson, 1937)
2.
B.
“The scientific method, as far as it is a method, is nothing more than
doing one’s damndest with one’s mind, no holds barred.” (Percy
Bridgman, 1950)
A “generic” scientific method usually contains these three parts
1. Making Observations:
a. Qualitative: the water is hot (no number involved)
b. Quantitative: the water is 100 oC (number and unit)
2.
Formulating Hypotheses: possible explanation for an observation
3.
Performing Experiments: test the hypothesis and gather new
observations
C.
Theories and Laws
1. Theory = set of tested hypotheses that explain a natural phenomenon
a. Observation: something you witness and can record
b. Theory: interpretation of why the observation occurred
c. Can always be questioned, revised, or disproved entirely
d. As science advances, new experiments can change the theory
2. Scientific Law = summary of countless observations behaving the same
a. Conservation of Mass: mass of reactants = mass of products
b. Not an explanation (as a theory is)
3. Example
Law: organisms evolve over time. Theory: natural selection
III.
Measurement
A. The Metric System (SI System) is used in chemistry
Physical Quantity
Mass
Name of Unit
Abbreviation
kilogram
kg
Length
meter
m
Volume
liter
L
B.
Volume measurement
1. Liter is not a fundamental unit,
but derived from the meter
2. 1 L = 0.001 m3 = 1 dm3 = (10
cm)3 = 1000 cm3 = 1000 ml
C.
Mass measurement
1. Mass is a measure of how much
matter an object contains
2. Mass is constant as long as matter
is not added or removed
3. Weight is the force that gravity
exerts on an object. This can
change depending where the
object is.
D.
Uncertainty in Measurement
1. We often must estimate the last number
of a measurement
2. The reading is near 20.15 ml, but
Some might read as 20.14 or 20.16
3. 20.1 are certain, the 4/5/6 is uncertain
4. You should report one uncertain digit
5. The certain + one uncertain digit = the significant figures for a
measurement (there are 4 significant figures for the volume above)
6. Unless stated otherwise, the uncertainty in the last digit is ±1
7. Example: What is the difference between 25 ml and 25.00 ml?
a. 25 ml means between 24 ml and 26 ml
b. 25.00 ml means between 24.99 and 25.01 ml
E.
Precision and Accuracy
1. Accuracy = how close to correct the measurement is
2. Precision = how reproducible the measurement is
Not Accurate
or precise
a)
Precise, but
not accurate
b)
F. Types of Error
1. Random Error: equal probability of
missing correct value on either side;
usually can’t be controlled (Indeterminate
Error).
2.
There are large random errors in figure (a),
and small random errors in (b) and (c).
3.
Systematic Error: occurs in the same
direction each time; can often be
controlled by correcting instrument or
adding correction factor to data
(Determinate Error).
Accurate and
4. There is no systematic error in (a) or (c),
Precise
but a large systematic error in (b).
c)
G. Example: Is a given graduated cylinder accurate?
1.
2.
3.
4.
Trial
Grad. Cyl. Vol. (ml)
Buret Volume (ml)
1
25
26.54
2
25
26.51
3
25
26.60
4
25
26.49
5
25
26.57
Average
25
26.54
Precision: very high because the buret values are all similar
Accuracy: low accuracy; the supposed value was 25 ml, but is closer to 26 ml
Random Error = small
Systematic Error = large (~ +1.5 ml)
5. Using average values from multiple measurements usually limits random error, but
this can’t account for systematic error