CHemistry Thingy - ACTIVITY 01-1 Units of Measurement WHY?...

1
W
HY
?
Units identify the scale that is used in making a measurement and are essential for the measurement
to be meaningful. For example, if someone tells you that a person is 60 tall, you do not know
whether they are referring to a child or possibly an adult until you know the units. The units could
be inches or centimeters, but probably are not feet or meters. In your study of chemistry and its
applications, you need to be familiar with the basic units that are used for mass, length, time,
temperature, electrical current, and amount of substance. Pre fi xes to the units make it quicker and
easier to write very large or very small numbers, e.g., 5,600,000 g = 5.6 Mg or 0.000001 s = 1 μ s.
Other units are derived from these basic units. For example, units of volume are derived from units
of length, and units of energy are derived from units of mass, length, and time. You also need to be
able to convert from one set of units to another because different countries, disciplines, and even
sub-disciplines of chemistry often use different units for the same quantity. For example, in the
United States speed limits are given as miles per hour; in many other countries speed limits are
given as kilometers per hour.
L
EARNING
O
BJECTIVES
• Identify the units used to measure physical quantities
• Become familiar with the pre fi xes used for larger and smaller quantities
• Master the use of unit conversion in solving problems
S
UCCESS
C
RITERIA
• Associate units with physical quantities
• Replace pre fi xes by multiplying by appropriate numerical factors
• Identify, set up, compute, and validate unit conversions
P
REREQUISITE
• Exponential notation
M
ODEL
1:
I
NTERNATIONAL
S
YSTEM OF
U
NITS
(SI U
NITS
)
Table 1
Physical Quantity Name of Unit Abbreviation
mass kilogram kg
length meter m
time second s
temperature Kelvin K
electrical current ampere A
amount of substance mole mol
(continued on the following page)
Units of Measurement
A
CTIVITY
01-1

Chapter 1: Nature of Chemistry
2
Foundations of Chemistry
M
ODEL
1:
I
NTERNATIONAL
S
YSTEM OF
U
NITS
(SI U
NITS
),
CONTINUED
Table 2
Pre fi x Abbreviation Meaning
tera T 10 12
giga G 10 9
mega M 10 6
kilo k 10
3
centi c 10
–2
milli m 10
–3
micro μ 10
–6
nano n
10
–9
pico p 10 –12
femto f 10
–15
Examples
Mass: A quarter-pound hamburger has a mass of 0.11 kg. 0.11 kg = 110 g
Length: A tall basketball player (7 feet) has a height of 2.15 m. 2.15 m = 215 cm = 2150 mm
Time: There are 3300 s in a 55 minute chemistry lecture. 3300 s = 3.300 ks
Temperature: Water freezes at 273 K.
1
×
10
3
g = 1000 g = 1 kg
1 cm = 0.01 m = 1
×
10
–2
m
10 cm
×
10 cm
×
10 cm = 1000 cm
3
= 1 L (Note: L = liter)
1 ps = 1
×
10
–12
s
K
EY
Q
UESTIONS
1. What are the 6 basic units and their abbreviations listed in Model 1 (Table 1)? (You need to have
these units and their abbreviations memorized. Writing them without looking at the table will help
you remember.)
2. What are the 10 pre fi xes listed in Model 1 (Table 2), along with their abbreviations and meanings?