CHAPTER 3:
MEASUREMENTS IN CHEMISTRY
CHAPTER 3:
MEASUREMENTS
IN CHEMISTRY
MEASUREMENT
SYSTEMS
SECTION 3.1
measurement
on
0
a comparison of an unknown quantity to a
known standard unit
-
MEASUREMENT: DIMENSIONS
demensions
Many phenomena have _____________
(measurable
~
quantities).
examples: length, mass, volume, time, and electrical charge
Each dimension has a unit of measure.
example: length—kilometer, mile, inch
Dimensional units are lined up on a scale to provide a means of
measuring.
MEASUREMENTS
A measurement consists of two parts:
8
a number
a unit
METRIC SYSTEM
Scientists need standardized
measurement units.
_
In 1670, French astronomer Gabriel Mouton proposed a metric
system which was based on a decimal scale.
Decimul
_____________—a
scale that consists of base units
multiplied by powers of ten
In 1960, many nations adopted the modern metric system—the
Système International d’Unités (the International System of
Units, SI).
scale
fundamental unit
_
θ
one of seven units in the SI that is based
on a physical constant
0
_
SI FUNDAMENTAL UNITS
1. ___________—measures
electrical current
ampere ( A )
Candela ( ed )
2. ___________—measures
light intensity
Kelvin ( K )
3. ___________—measures
temperature
4. ___________—measures
mass
KTlogram ( kg )
)
5. ___________—measures
length
meter (
ㅣ
m
mole cmole )
6. ___________—measures
number of particles
second ( s )
7. ___________—measures
time
‰
K
kg
m
밤이
e
derived unit
~
units
in the SI that are mathematical
→
combinations of fundamental units
_
_
combination
DERIVED UNIT: EXAMPLES
newton ( N )
___________—the
unit of ~
force
Oomnumi
kg m rs
N=
O
s2
쁨
___________—the
unit of energy, work, and heat
joule ( J )
⑩
O
kg m2
J=
s2
DERIVED UNIT: EXAMPLES
∞
___________—the
unit of pressure
pascal ( Pa )
_
kg
Pa =
m s2
~
~
>
10805m 10
엌
'
쁘
msz
읍 틈
틋
SI DERIVED UNITS
square meter (m2)
ared
cubic meter (m3) volume
kilogram per cubic meter (kg/m3) density
hertz (Hz) frequency
newton (N) force
pascal (Pa) pressure
joule (J) energy
degree Celsius (°C) temperture
SI UNIT PREFIXES
Scientists sometimes need to scale units up or down in order to
measure and express quantities of different sizes.
example: measuring the length of your shoe vs. the distance
from your house
To change the size of a unit, the SI adds prefixes representing
powers of ten to the names of the base units.
example: meter—millimeter, centimeter, kilometer
unit conversion
the mathematical process used to change
a measurement in one unit into an
equivalent measurement using a different
unit
UNIT CONVERSION
conversion factor—a factor that is used to convert between units
the ratio of two equivalent measures; always equal to 1
a fraction that contains both the original unit and its equivalent
value in a new unit
dimensional analysis—a process of treating units as if they were
variables in math
EXAMPLE 3-1
Convert 55.6 in. into feet.
55.6 in. = ? ft
Ift
=
12 ih
55.6 in. 1 ft = ? ft
12 in.
55.6 ft = 4.63 ft
12
55.6 in. ft = ? ft
in.
EXAMPLE 3-2
Convert 132 547 cm to m.
102 m 1325.47 m
132 547 cm
=
= 1325.47 m
1
1 cm
132 547 cm
1m
= 132 547 m = 1325.47 m
100 cm
100
EXAMPLE 3-3
Convert 356 kg to μg.
1000 g 1000000 μg 356 000 000 000 μg
356 kg
=
1
kg
1
g
1
= 356 000 000 000 μg
= 3.56 ? 011 μg
EXAMPLE 3-4
Convert the density of iron from 7.874 g/cm3 into kg/m3.
g 1 kg 100 cm 3 7 874 000 kg
7.874
=
3 1000 g
3
cm
1m
1000 m
= 7874 kg/m3
3.1 SECTION REVIEW
1. What do we call the process by which scientists quantify their
observations of their surroundings?
2. What is a dimension?
3. What measuring system is used by scientists around the world?
3.1 SECTION REVIEW
4. Explain how a measurement system is a model. Why is it
important that scientists have a standardized system?
3.1 SECTION REVIEW
5. Explain one of the three reasons for the almost worldwide
usage of the SI.
3.1 SECTION REVIEW
6. What is the SI fundamental unit for temperature, and on the
basis of what physical constants is it defined?
3.1 SECTION REVIEW
7. Write an equation that states the relationship between the
given units, then write a conversion factor that could be used
to convert the first unit to the second.
a. grams and micrograms
b. femtometers and meters
3.1 SECTION REVIEW
7. Write an equation that states the relationship between the
given units, then write a conversion factor that could be used
to convert the first unit to the second.
c. liters and hectoliters
d. gigahertz and hertz
3.1 SECTION REVIEW
8. Convert the following measurements.
a. 3.8 × 1010 bytes to gigabytes
b. 475 nm to meters
3.1 SECTION REVIEW
8. Convert the following measurements.
c. 27.3 kL to milliliters
d. 5.67 Mg to micrograms
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