Chapter 1, cont’d: Units of Measurement
Measured quantities are associated
with units!!
1. Base units in the SI system:
Mass
kilogram (kg)
Length
meter (m)
Time
sec (s)
Quantity
mole (mol)
Temperature Kelvin (K)
From the base units come derived units, e.g.,
Density = mass/volume
Velocity = distance/time
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Review of Exponential Notation (Appendix A1)
e.g., express the following in scientific notation:
0.001453 m3 (what is this a measure of?)
33987.22 sec
SI system uses prefixes to indicate decimal fractions or
multiples of units, e.g.,
Kilo-
k
1x103
Centi-
c
1x10-2
Milli-
m
1x10-3
Micro- 
1x10-6
Nano-
1x10-9
n
LOOK OVER TABLE 1.5 (Common SI Prefixes)
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e.g., use appropriate metric prefixes (k-, p, n, etc) to
express the following measurements without an exponent:
6.5 x 10-9 m
3.5 x 103 L
6.54 x 105 s
Temperature
What is temperature?
Temperature scales
Celsius
0oC= freezing point of H2O
100oC=boiling point of H2O (at sea level)
-What are the corresponding temps in oF?
Conversions between oC and oF
o
C = 5/9(oF - 32o)
o
F = 9/5(oC) + 32o
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Kelvin scale
0 K = -273.15 oC
(absolute zero)
K = oC + 273.15
Density (D)
D = mass / volume
What are the base SI units of density?
More common: units of g/cm3
-Do density and weight describe the same thing?
Is density an intensive property of matter or an extensive
one?
Calculations using density
Find the density (g/cm3) of Hg if 1.00x102 g of this
substance occupies a volume of 7.45 cm3
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2. Uncertainty in Measurement
Uncertainties always exist in measured quantities.
Why?
Exact and Inexact Numbers
Exact: any counted quantity; any conversion factor
Inexact: any measured quantity
Precision and Accuracy
precision: how closely individual measurements agree
with each other
accuracy: how closely individual measurements agree
with the "correct" value
Significant Figures
Measured quantities are reported such that only the
last digit is uncertain
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e.g., a penny has a mass of 1.5576 g. This implies that the
uncertainty in the mass of the penny is  0.0001 g.
How many significant figures are reported in the mass
of the penny?
How do we determine the number of significant figures in
a measured quantity?
Rules to live by:
all nonzero digits are significant (893 cm ; 17.57 L)
zeros between nonzero digits are significant (1.005
mol; 104 kg)
zeros to the left of the first nonzero digit are NOT
significant (0.05 mol)
zeros at the end of a number AND to the right of the
decimal point ARE significant (0.0200 mol; 3.0 cm)
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OK, what about a number which ends in zeros that are not
to the right of the decimal point? (120g, 11500 cm)
write the number in scientific notation:
e.g., 120 g = 1.20x102 g (3 sig figs)
11500 cm = 1.1500x104 cm (5 sig figs)
Significant figures in calculations involving measured
quantities
The precision of the calculated result is limited by the
least precise measurement!!!!!
Multiplication and division
result must have no more sig figs than the
measurement with the fewest sig figs
e.g.: Suppose that a 1.05 g sample of a metal had a volume
of 23.610 cm3. Find the density in g/cm3.
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If the result has more than the correct number of sig figs,
it must be rounded off:
e.g., round 0.006543210 nm to four sig figs and report
in scientific notation
In calculations with intermediate steps, retain an extra sig
fig or two through the calculations and round the final
result to the correct number of sig figs!
e.g.: The maximum allowable concentration of CO
in urban air is 10.0 mg/m3 over an 8-hour period.
At this level, what mass of CO in mg is present in
a room measuring 8.0 x 12.1 x 10.1 m?
3. Dimensional Analysis/Conversions
Length
Given that 1 m = 1.0936 yd, and 1 inch = 2.54 cm,
how many inches are in 2.5 m?
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Convert 0.0023 mm to nm
Volume
SI unit of volume = m3
More common: cm3 (or cc) or
dm3
1 liter (L) = 1000 ml = 1000
cm3
Given that 1 L = 1.057 qt, how many L is 5 gal of
gasoline?
Convert 55.35 ft3 to cm3
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The density of air is 1.19 g/L. What is the mass, in kg, of
the air in a room that measures 12.5 x 15.5 x 8.0 ft?
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Problems du Jour
Perform the following conversions:
5.0 x 10-8 m to nm
1.55 kg/m3 to g/L
5.0 pm/s to m/s
An individual suffering from high blood cholesterol
has a count of 232 mg cholesterol/100 mL blood. If
the total blood volume is 5.2 L, how many g of total
blood cholesterol does this person contain?
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