Chapter 2
Measurements in Chemistry
Chemistry 2A
Data
• Qualitative
– Data obtained from
one’s opinion
– Does not involve
numbers
• Quantitative
– Data obtained from
measurements
– Involves numbers
U.S. Customary System
• Also called:
– American System
– English System
•
•
•
•
Inch
Gallon
Pound
Teaspoon
Metric System
• Système International (SI)
• International decimalized system of
measurement
• First adopted by France in 1791
• Meter
• Gram
• Liter
Length
• How long something is, DUH!
• SI unit = meter (m)
Mass
• Measure of the quantity of matter (stuff) in
an object
• SI unit = Kilogram (kg)
Volume
• The amount of space that an
object or substance
occupies.
• SI unit = Cubic meter (m3)
• 1 L = 0.001 m3
• 1 L = 1000 mL
• 1 mL = 1 cm3 = 1 cc
Time
• Duration of event
• SI unit = Second (s)
French Revolutionary Clock
System International (SI) Units
Prefix
Giga
Mega
Kilo
Hecto
Deka
No prefix
(Unity)
Deci
Centi
Milli
Micro
Nano
Pico
Symbol
G
M
k
h
da
Multiple
109
106
103 = 1000
102 = 100
101 = 10
100
d
c
m
10-1 = 0.1
10-2 = 0.01
10-3 = 0.001
μ
n
p
10-6
10-9
10-12
Example
Gigabyte = Gbyte
Kilogram = kg
Meter, liter, gram =
m, L, g
Milliliter = mL
Nanometer = nm
Common Units and Their Equivalents
Length
1 kilometer (km)
1 meter (m)
1 meter (m)
1 foot (ft)
1 inch (in.)
=
=
=
=
=
0.6214 mile (mi)
39.37 inches (in.)
1.094 yards (yd)
30.48 centimeters (cm)
2.54 centimeters (cm) exactly
Common Units and Their Equivalents
Mass
1 kilogram (km) = 2.205 pounds (lb)
1 pound (lb) = 453.59 grams (g)
1 ounce (oz) = 28.35 grams (g)
Volume
1 liter (L)
1 liter (L)
1 liter (L)
1 U.S. gallon (gal)
=
=
=
=
1000 milliliters (mL)
1000 cubic centimeters (cm3)
1.057 quarts (qt)
3.785 liters (L)
Problems
1) Green light has a wavelength of
approximately 550 nm. What is this
value in meters? Picometers?
Kilometers?
2) Your neighbor lost 50 pounds after
having a baby. How many kg did she
lose? How many micrograms?
3) How many milliseconds in a year?
Dimensional Analysis
• Using units as a guide to problem solving
is called dimensional analysis
• Figure out which unit you want to start
with and which one you want to get to
• Use conversion factors to get there
– Relationship between two units
– May be exact or measured
– Generated from equivalence statements
• Always include units in your calculations!
12 eggs = 1 dozen
Temperature
• A measure of the average kinetic
energy of the particles in a
sample of matter, expressed in
terms of units or degrees
designated on a standard scale.
• A physical property that
determines the direction of heat
flow in an object upon contact
with another object.
• Fahrenheit (°F), Celsius (°C),
Kelvin (K)
Fahrenheit (ºF), Celsius (ºC), Kelvin (K)
•
•
•
•
ºF = ºC(1.8) + 32
ºC = (ºF – 32)/1.8
K = ºC + 273
ºC = K – 273
Lord William Thomas Kelvin
Problems
1) If it’s 35ºC in London, would you say that
it’s probably winter or summer? What is
this temperature in Kelvin?
2) You are feeling sick and decide to take
your temperature. Your thermometer,
which only reads temps in Kelvin, says
that you are at approximately 312 K. Do
you have a fever?
Density
• The ratio of the mass of an object to its
volume
Mercury
Water
13.6 g/cm3
1.0 g/mL
8.94 g/cc
Problems
1) Calculate the density of the
rock in the picture to the
right. The rock has a mass of
29.5g.
2) What is the mass of 5.5mL
of mercury if Hg has a
density of 13.53 g/mL?
3) Calculate the height of the
piece of wood to the right.
Oregon Pine d = 0.53 g/mL
Scientific Notation
1) Locate the decimal point
2) Move the decimal so that there is only one
number to the left of it
3) Write “x 10” behind you new number
4) Count the number of places you’ve moved your
decimal point and make this number the
exponent on your 10
5) Assign a + or – sign to your exponent
a) If your original # is larger than your SN #, the
exponent is +
b) If your original # is smaller than your SN #, the
exponent is –
Problems
Write the following standard numbers in scientific
notation and write the numbers in scientific notation
in standard form.
1)
2)
3)
4)
5)
6)
7)
252
342888
0.0047
0.000008
3.33 x 102
4 x 10-4
35000
Significant Figures
•3
• 3.0
• 3.00
• Scientific measurements are reported so that
every digit is certain except the last, which
is estimated
Certain
Uncertain
Rules for Significant Figures
1) Numbers up to and including the
“uncertain” number are significant
2) All non-zero numbers are significant
3) Zeros may or may not be significant
4) Zeros are significant if
a) They are between two non-zero digits
b) They are at the end of a decimal number
5) Zeros are not significant if
a) They are used as place holders in large
numbers without a decimal point
b) They are at the beginning of decimal numbers
6) All numbers displayed in a number written
in scientific notation are significant
Problems
Identify the correct number of significant digits in the
figures below.
1)
2)
3)
4)
5)
45
45.0
405
4050
4050.
6) 0.000405
7) 0.00040500
8) 900.00
9) 4.0 x 103
10) 3 x 108
Mt. Everest
29000 ft, 2.9000 x 104 ft., or 29002 ft?
Calculation With Significant Digits
• Multiplication and Division
– The final answer has the same number of sig figs
as the measurement with the fewest sig figs
– Example 1:
• 22.2 cm x 3.4654 cm = ?
– Example 2:
• 0.0009 mm / 0.340 mm = ?
• Addition and Subtraction
– The final answer is written so that it has the
same number of decimal places as the
measurement having the fewest decimal places
– Example 1:
• 44.4 L + 2.3967 L + 0.000002 L = ?
– Example 2:
• 4107 in – 608.7 in = ?
Problems
1)
2)
3)
4)
200 • 3.44 • 9.30
0.00309 / 4.4 x 103 • 999
24.464 – 10.63 – 2.2
0.000800 + 909 + 3.6
Precision and Accuracy
• Precision: how well several determinations
of the same measurement agree
– Reproducibility/repeatability
• Accuracy: agreement of a measurement
with the accepted value
Determine whether the following students
exhibit good or poor accuracy and precision
Exam 1
Exam 2
Student A
99%
100%
Student B
100%
89%
Student C
59%
59%
Student D
25%
49%
Accuracy &
Precision