Chemistry
Chapter 3
Scientific Measurement
Scientific Notation
Convert to or from Scientific
Notation:
A) 241
2.41 x 102
D) 0.512
5.12 x 10-1
B) 6015
6.015 x 103
E) 6.62 x 102
662
C) 0.0162
1.62 x 10-2
F) 3.4 x 10
0.0034
-3
Accuracy -how close measurements
are to the correct or accepted value.
Precision - closeness of a set of
measurements.
Percent error – compares the accuracy
of an individual value or average
values to the correct or accepted
value.
% error =
Accepted value – Experimental value x 100%
Accepted value
STAAR CHART FORMAT
Example: What is the percent error for a
mass measurement of 17.7g, given that the
correct value is 21.2g?
% error = 21.2g – 17.7g x 100% =
21.2g
16.5%
Significant Figures Rules
1. Nonzero Digits – every nonzero
digit is significant.
Ex: a) 32.8 m has three sig figs
b) 981.78 km has five sig figs
2. Sandwich zeros – zeros appearing
between nonzero digits are
significant.
Ex: c) 101.2 g has four sig figs
d) 50.1 L has three sig figs
3. Placeholder – leftmost zeros
appearing in front of nonzero digits
are not significant.
Ex:
e) 0.000007 has one sig fig
f) 0.0003809 has four sig figs
4. Trailer zeros – zeros at the end of
a number and to the right of the
decimal point are significant.
Ex: g) 2000. m has four sig figs
h) 34.0 mL has three sig figs
Uncertainty in
Measurement
STAAR CHART FORMAT FOR
SIG. FIGS.
Rounding
*The calculated value cannot be more
precise than the measured values
used to obtain it.
Example: Round each measurement to
the three sig. figs.
a) 45.89m
45.9m
c) 17.32 cm
17.3 cm
b) 3004 m
3.00 x 103m
d) 20019 L
2.00x104 L
Rounding – Addition and
Subtraction
Round the answer to the same number
of decimal places (not digits) as the
measurement with the least number
of decimal places.
Example: Subtract 2.6103m
from 5.44m.
5.44
m
- 2.6103 m
2.8297 m
2.83m
Rounding – Multiplication and
Division
Round the answer to the same number
of sig. figs as the measurement with
the least number of sig. figs.
Example: Multiply 2.4 m2 and
15.82m.
2.4 m2 x 15.82 m = 37.968 m3
38 m3
Extra Practice
SI Measurement – Le Systeme
International d’Unites
7 SI Base Units
Quantity
Symbol
Unit Name
Unit
Abbreviation
l
m
t
T
n
meter
kilogram
second
Kelvin
mole
m
kg
s
K
mol
Electric Current
I
ampere
A
Luminous Intensity
Iv
candela
cd
Quantity
Length
Mass
Time
Temperature
Amount of
Substance
SI Prefixes
Prefix
kilo
Unit
abbreviation
Exponential
factor
k
103
100
Example
1 kilometer(km)= 1000 m
1 meter (m)
deci
d
10-1
centi
c
10-2
100 centimeter (cm) = 1m
milli
m
10-3
1000 millimeter (mm) = 1m
micr
o
nano
u
10-6
1000000 micrometer (um) =1m
n
10-9
10 decimeter(dm) = 1 m
1000000000 nanometer (nm) = 1m
Mass – measure of the quantity of
matter (SI unit is kg).
The gram, g, is ideal for expressing
masses of small objects such as a
beaker.
For even smaller masses like weighing
out chemicals the milligram is used.
Mass vs Weight
Mass is the measure of the amount of
matter, whereas weight is the
measure of the gravitational pull on
matter.
Derived units are a combination of SI
base units.
*Volume is the amount of space
occupied by an object. The derived
unit for volume is cubic meters, m3.
(Volume = l x w x h)
Figure 01.20
Density is a derived unit. It is mass
divided by volume.
density =
mass
volume
or
The SI units are kg/m3
D=m
V
Density…:
• is a physical property of a substance.
• does not depend on the size of the
sample.
• As the mass of the sample increases
so does the volume.
Density of a substance determines
whether it floats or sinks in a liquid.
For instance, ice has a density of 0.92
g/mL, which is less than that of water
(0.998 g/mL). Since ice is less dense,
it will float on water.
Example: The density of water is 0.998 g/mL. If
copper pellets were placed in the water would it
sink or float? (Density of copper is 8.92g/mL)
The copper would sink as its density is
higher than that of water.
Examples:A sample of aluminum metal has a
mass of 8.40g. The volume of the sample is 3.1cm3.
Calculate the density of aluminum.
D=m
V
= 8.40g
3.1cm3
= 2.7g/cm3
A sheet of metal has a length of 32.0cm, a width of
2.00cm, and a height of 1.000cm. The density
of the metal is 9.7g/cm3. Calculate the mass
of the metal.
D = m/V
m=DxV
m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm)
m=
620 g
Specific Gravity
• Comparison of the density of a
substance with the density of a
reference substance.
• A hydrometer is used to measure the
specific gravity of a liquid.
Temperature
• Determines the direction of heat
transfer.
Temperature Scales
• Celsius scale: Uses water as the
reference (i.e. 0oC and 100oC)
Temperature Scales (cont.)
• Kelvin scale: Freezing point of water
is 273.15 K and its boiling point is
373.15 K.
– Absolute Zero – all motion ceases
Converting between Celsius
and Kelvin
K = oC + 273
oC = K – 273
Liquid nitrogen boils at 77.2 K. What is
this temperature in degrees Celsius?
oC
= K – 273
oC = 77.2 – 273
-195.8oC