2.C Units of
Measurement
Making Observations
2 types of info:
 Quantitative-numerical (usually
numbers)
 Qualitative- descriptive (usually words)
Measurement
 Quantitative
information (quantity)
 Need a number and a unit (most of time)
 For example: 7.5 centimeters



7.5 is number
Centimeters is unit
Length is quantity
 Units
compare what is being measured to
a defined measurement standard
SI Measurement
Systeme International d’Unites : SI
 System of measurement agreed on all
over the world in 1960
 Units are defined in terms of standards of
measurement
 Le
Important SI Base Units
Quantity
Length
Symbol Unit
l
meter
Abbreviation
m
Mass
m
kilogram
kg
Time
t
second
s
Temperature
T
Kelvin
K
Amount
n
mole
mol
Mass
 Measure
of the quantity of matter
 SI unit: kg
 use g a lot too
 mass vs. weight



weight is the measure of gravitational pull on
matter
mass does not depend on gravity
on a new planet, mass would be same but
weight could change
Length
 SI
unit: m
 use cm & km a lot too
Derived SI Units
 come
from
combining base
units
 Example: Area
A = length x width
A = 8cm x 7cm
A = 56 cm2
Volume
 amount
of space occupied by object
 SI: m3 = m x m x m
 use cm3 in lab a lot
 **Need to know: 1 cm3 = 1mL
1000mL = 1L
Density
 ratio
of mass to
volume
kg
 SI:
mass
Density 
volume
m3
 Intensive property of matter (doesn’t
change with amount )
Example
A sample of Al metal has a mass of 8.4 g.
The volume is 3.1 cm3. Find the density.
 Convert
3 years to weeks
then to days
then to hours
then to minutes
then to seconds.
Prefixes

Prefixes are added to the base unit names to
represent quantities smaller or larger
M
mega
106
1,000,000
larger
k
kilo
103
1,000
larger
c
centi
10-2
1/100
smaller
m
milli
10-3
1/1000
smaller
μ
micro
10-6
1/1,000,000
smaller
Conversion Factors
 ratio
that comes from a statement of
equality between 2 different units
 every conversion factor is equal to 1
Example:
statement of equality
conversion factor
4quarters  1dollar
Guidelines for Conversions
 consider
what unit you are starting and
ending with (know, want to know)
 always cancel units as you go
Example 1
Convert 5.2 cm to mm

Known: 100 cm = 1 m
1000 mm = 1 m
Example 2
Convert 0.020 kg to mg

Known: 1 kg = 1000 g
1000 mg = 1 g
Example 3
Convert 500,000 μg to kg

Known: 1,000,000 μg = 1 g
1 kg = 1000 g
Advanced Conversions
 One
difficult type of conversion deals with
squared or cubed units
 Be sure to square or cube the conversion
factor you are using to cancel all the units
Example

Convert:
2000 cm3 to m3
Known:
100 cm = 1 m
cm3 = cm x cm x cm
m3 = m x m x m
Advanced Conversions
 Another
difficult type of conversion deals
units that are fractions themselves
 Be sure convert one unit at a time; don’t
try to do both at once
 Work on the unit on top first; then work on
the unit on the bottom
 Setup your work the exact same way
Example

Convert:
350 g/mL to kg/L
 No intermediate
needed
OR
Known:
1000 g = 1 kg
1000 mL = 1 L
Combination Example

Convert: 7634 mg/m3 to Mg/L
Known:
1000 mg = 1 g
1,000,000 g = 1 Mg
100 cm = 1 m
1 cm3 = 1 mL
1000 mL = 1 L