Chemistry: Matter and Change

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Analyzing Data
Section 2.1 Units and
Measurements
Section 2.2 Scientific Notation and
Dimensional Analysis
Section 2.3 Uncertainty in Data
Section 2.4 Representing Data
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Section 2.1 Units and Measurements
• Define SI base units for time, length, mass, and
temperature.
• Explain how adding a prefix changes a unit.
• Compare the derived units for volume and density.
mass: a measurement that reflects the amount of
matter an object contains
Section 2.1 Units and Measurements
base unit
kelvin
second
derived unit
meter
liter
kilogram
density
Chemists use an internationally
recognized system of units to
communicate their findings.
(cont.)
Standards of Measurement
2
Units and Standards
• A standard is an
exact quantity
that people
agree to use to
compare
measurements.
Standards of Measurement
2
Measurement Systems
• Suppose the label on a ball of string indicates
that the length of the string is 150.
• Is the length 150 feet, 150 m, or 150 cm?
• For a measurement to make sense, it must
include a number and a unit.
Standards of Measurement
2
Measurement Systems
• The English system of
measurement is
commonly used in the
United States.
• Most other nations use
the metric system—a
system of
measurement based
on multiples of ten.
Standards of Measurement
2
International System of Units
• All SI standards are
universally
accepted and
understood by
scientists
throughout the
world.
Standards of Measurement
2
International System of Units
• Each type of SI
measurement has
a base unit.
• The meter is the
base unit of length.
Standards of Measurement
2
International System of Units
• Every type of quantity
measured in SI has a
symbol for that unit.
• All other SI units are
obtained from these
seven units.
Standards of Measurement
2
SI Prefixes
• The SI system is
easy to use
because it is
based on multiples
of ten.
Standards of Measurement
2
SI Prefixes
• Prefixes are used
with the names of
the units to indicate
what multiple of ten
should be used with
the units.
• The most frequently
used prefixes are
shown.
Standards of Measurement
2
Converting Between SI Units
• A conversion factor is a ratio that is equal to
one and is used to change one unit to
another.
• For example, there are 1,000 mL in 1 L, so
1,000 mL = 1 L.
Standards of Measurement
2
Converting Between SI Units
• To convert units, you multiply by the
appropriate conversion factor.
• For example, to convert 1.255 L to mL, multiply
1.255 L by a conversion factor.
Standards of Measurement
2
Converting Between SI Units
• Use the conversion factor with new units
(mL) in the numerator and the old units (L) in
the denominator.
Standards of Measurement
2
Measuring Distance
• In scientific measurement length is the
distance between two points.
• The SI base unit of length is the meter, m.
• Metric rulers and metersticks are used to
measure length.
Standards of Measurement
2
Choosing a Unit of Length
• The size of the
unit you measure
with will depend
on the size of the
object being
measured.
• You probably would use the centimeter to
measure the length of your pencil and the meter
to measure the length of your classroom.
Standards of Measurement
2
Choosing a Unit of Length
• By choosing an appropriate unit, you avoid
large-digit numbers and numbers with many
decimal places.
• Twenty-one kilometers is easier to deal with
than 21,000 m. And 13 mm is easier to use
than 0.013 m.
Standards of Measurement
2
Measuring Volume
• The amount of space occupied by an object
is called its volume.
• If you want to know the volume of a solid
rectangle, such as a brick, you measure its
length, width, and, height and multiply the three
numbers and their units together (V = 1 x w x
h).
Standards of Measurement
2
Measuring Volume
• For a brick, your measurements probably
would be in centimeters.
• The volume would then be expressed in cubic
centimeters, cm3.
Standards of Measurement
2
Measuring Liquid Volume
• In measuring a liquid’s volume, you are
indicating the capacity of the container that
holds that amount of liquid.
• The most common units for expressing liquid
volumes are liters and milliliters.
Standards of Measurement
2
Measuring Liquid Volume
• A liter occupies the same volume as a cubic
decimeter, dm3.
• A cubic
decimeter is
a cube that
is 1 dm, or
10cm, on
each side.
Standards of Measurement
2
Measuring Liquid Volume
• Sometimes, liquid volumes such as doses of
medicine are expressed in cubic centimeters.
• Suppose you wanted to convert a
measurement in liters to cubic centimeters.
• You use conversion factors to convert L to mL
and then mL to cm3.
Units
• Système Internationale d'Unités (SI) is an
internationally agreed upon system of
measurements.
• A base unit is a defined unit in a system of
measurement that is based on an object or
event in the physical world, and is
independent of other units.
There are four
main categories of
measurement
• Time
• Length
• Matter/mass
• Temperature
25
Each category of
measurement has a
base unit
• Time – second (s)
• Length – meter (m)
• Matter/mass – gram
(g)
• Temperature –
Kelvin (K)
26
Units (cont.)
• The SI base unit of temperature
is the kelvin (K).
• Zero kelvin is the point where
there is no particle motion or
kinetic energy, also known as
absolute zero.
• Two other temperature scales
are Celsius and Fahrenheit.
• Some measurements
are considered to be
derived units. For
example, density is a
mass to volume
comparison and can
be calculated using the
following equation:
• d = m/v
28
• Volume is considered
to be a derived unit.
Why?
29
Standards of Measurement
2
Measuring Volume
• The amount of space occupied by an object
is called its volume.
• If you want to know the volume of a solid
rectangle, such as a brick, you measure its
length, width, and, height and multiply the three
numbers and their units together (V = 1 x w x
h).
Section 2.1 Assessment
Which of the following is a derived unit?
A. yard
B. second
C. liter
D
C
A
0%
B
D. kilogram
A. A
B. B
C. C
0%
0%
0%
D. D
Section 2.1 Assessment
What is the relationship between mass
and volume called?
A. density
B. space
D
A
0%
C
D. weight
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. matter
Section 2.3 Assessment
A substance has an accepted density of
2.00 g/L. You measured the density as
1.80 g/L. What is the percent error?
A. 0.20 g/L
A
0%
D
D. 0.90 g/L
C
C. 0.10 g/L
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. –0.20 g/L
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