PreAP Chemistry Chapter 2 Notes
2.1 Scientific Method
The Scientific Method is a logical approach to solving problems by observing and collecting
____________________, formulating hypotheses, testing hypotheses, and formulating theories that are supported by
data.
There are two kinds of data that can be observed and collected: Qualitative and Quantitative.
 ____________________data is data about qualities, like appearance and behavior.
 ____________________data is data about quantities, like mass, density, and other numerical amounts.
A ____________________is based on previously collected data and is an attempt to ____________________the
data, as a testable prediction; if A, then B. (It may not necessarily contain the words “if” and “then”). A hypothesis
is tested with an ____________________.
In an experiment, usually the affect of one variable on another is tested. The variable that is being controlled
directly by the experimenter is the ____________________variable. The independent variable should then have an
affect on the variable being tested, called the ____________________variable.
Often there are additional variables that can be involved in an experiment, so care should be taken to be sure that
these are held ____________________. In addition, to judge if the independent variable actually did affect the
dependent variable and nothing else, a ____________________situation should be used. This could be a separate
specimen to which the independent variable is purposely held constant or is in the ‘usual’ state, or could be a
separate ____________________of the same experiment, during which the independent variable is held constant or
in the ‘usual’ state..
If a hypothesis is not disproved after many experiments to test it, then the hypothesis is considered a
____________________, like gravity or evolution.
2.2 Units of Measurement
Horses are measured in ____________________. This used to literally mean how many hand widths to go down the
side of the horse. For someone with small hands their horses will seem bigger than someone with big hands.
To avoid these issues in science, scientists have adopted SI Units. (SI = Système International, French for
International System.) These base units have been agreed on by the scientific community and will be used in this
class.
Quantity
Length
Mass
Volume
Time
Temperature
Amount of
Substance
Electric Current
Quanitity Symbol (in
equations)
Base Unit Name
l
m
V (uppercase)
t
T (uppercase)
n
meter
kilogram
liter
second
Kelvin
mole
Abbreviation (to use as a label
on numbers)
m
kg
L (uppercase)
s
K (uppercase, no “°”)
mol
I (uppercase)
ampere
A (uppercase)
____________________is a quantity of matter and is constant. Do not confuse it with weight! Astronauts on the
moon have less weight, but not less mass (less mass would mean they were shrinking!)
 1 kilogram is the same mass as 2.204622621849 pounds (but we'll use 2.20 lbs for this course)
____________________is the distance between two points.
 1 inch = 2.54 centimeters (exactly)
____________________is the measurement of heat intensity (more about this later).
 1 Kelvin is the same magnitude as 1 °C
 0 ºC = 273.15 K
A ____________________is a count of something, like a dozen. By definition this is an exact count and not a
measurement, but of course no one can count six hundred two sextillion two hundred fourteen quintillion one
hundred and fifty quadrillion, so the number is determined mathematically. The best calculation is currently
602,214,150,000,000,000,000,000. Most often for this course the rounded off number below will be used.
 1 mole = ____________________ “particles” or things
The beauty of the SI units is that almost all of them can be scaled up or down by factors of ten with relative ease.
Often once this is done a new ____________________is added to base unit to indicate the new unit of
measurement. You will need to understand and be able to use these prefixes for this course. Be sure to note which
abbreviations use lowercase and uppercase letters! This distinction is very important. For example m and M are
two different orders of magnitude.
Prefix and Symbol
Mega (M)
Kilo (k)
Hecto (h)
Deka (da or dk)
Base Unit (m, L, g)
Deci (d)
Centi (c)
Milli (m)
Micro (µ)
Nano (n)
Pico (p)
Meaning
1,000,000
1,000
100
10
1
0.1
0.01
0.001
0.000001
0.000000001
0.000000000001
one-tenth
one-hundredth
one-thousandth
one-millionth
one-billionth
one-trillionth
Exponetial Factor
106
103
102
101
1
10-1
10-2
10-3
10-6
10-9
10-12
____________________units are ‘new’ units that are made by combining two or more of the standard units
together. Below are several derived units, how they are derived, and the usual SI units used with each. There are
many, many more derived units.
Derived Unit
Origin
mass per unit volume
Usual SI Units
g/m3 = g m-3 or
g/cm3 = g cm-3 or
g/L = g L-1 or
g/mL = g mL-3
Density
Volume
Pressure
length × width × height
Force per unit area
L or m3 or cm3
Pascals (Pa)
____________________ ____________________ are a ratio derived from the equality between two different units
that can be used to convert from one unit to the other. For example:
4 quarters
1 dollar
or
1 dollar
4 quarters
or even
0.25 dollars
1 quarter
Conversion factors allow a quantity measured one way to be converted into a different way of measuring (although
the overall amount should never change).
Sometimes several conversion factors are used in the same calculation, but it is important to note that units in the
____________________will cancel with identical units in the ____________________. This process is called the
factor label method or ____________________ ____________________. For example:
How many quarters are in 6.53 dollars?
6.53 dollars
How many centimeters are in 2.34 miles?
4 quarters
1 dollar
= 26.12 quarters
2.34 miles
5280 feet
1 mile
12 inches
1 foot
2.54 cm
1 inch
= 376,586.496 cm
Practice Questions.
1. Convert 65.22 mg to g
______________________________________________________
2.
Convert 0.84 m to cm
______________________________________________________
3.
Convert 462 mL to L
______________________________________________________
4.
Convert 0.576 hg to kg
______________________________________________________
5.
Convert 31.5 cg to mg
______________________________________________________
6.
Convert 0.761 km to cm
______________________________________________________
7.
Convert 0.143 hours to seconds
_________________________________________________
2.3 Using Scientific Measurements
When scientists make measurements, there is usually a little discrepancy in the measurements due to many reasons,
often human error. For example, the same person could measure a string three different times and get three,
slightly-different measurements. For this reason, when making measurements or reading someone else’s
measurements it is important to consider the accuracy and precision of those measurements.
____________________refers to how close the measurement is to the real or accepted value.
____________________is how close a group of measurements of the same thing are to each other. The precision of
a series of measurements is usually easy to determine just by looking at them, but this is not the case with the
accuracy.
To find the level of accuracy of a measurement, the ____________________ ____________________ is calculated.
To make the calculation the accepted value (the value you were supposed to get) and the value you actually did get
during the experiment are needed. Then use this equation:
Percent error =
Accepted value – Experimental value
Accepted Value
× 100
The label to your percent error is the “%” sign.
For example; An experiment finds the density of lead to be 10.95 g/cm3. The textbooks states the density should be
11.34 g/cm3. What was the percent error for this experiment?
Percent error =
11.34 g/cm3 – 10.95 g/cm3
11.34 g/cm3
× 100 = 3.439 %
Practice Questions:
1. Sara’s lab shows the atomic mass of aluminum to be 28.9. What is her percent error if the accepted value is
27.0?
2. What is the percent error in a measurement of the boiling point of bromine if the textbook value is 59.35 °C and
the lab value is 40.6 °C?