CHEMISTRY IS
LARGELY A
QUANTITATIVE SCIENCE
Theories and ideas are tested by
measurement
Measurements are usually quantitative –
have numbers
Science is built on a foundation of
mathematics.
In recording measurements, it is necessary to
understand
1. SIGNIFICANCE of numbers
2. importance of UNITS.
Learning Objectives about
Units
1. Understand importance of units in
measurement
2. Identify common “metric” units
3. Apply common metric prefixes
4. Use simple unit conversions
5. Perform simple density
calculations
Scientific method and experiment
Hypothesis
proposes
relationship
between
sweetness and
size of oranges
Experiment tests
hypothesis with
measurement
Systems of measurements: the
“old”
English System - what the United States
uses today derived from the 'Kings" feet
(Old England). Also known as the United
States Customary System (USCS)
Units
1 foot (“big feet")
1 inch (knuckle)
1 yard (King Henry I - nose to thumb)
System Internationale (S.I.): the
“new”
The creation of the decimal Metric
System at the time of the French
Revolution and the creation of two
platinum standards representing the
meter and the kilogram was the first
step in the development of the
present International System of
Units.
Science has adopted the S.I. When
we say “metric” we mean S.I.
Know one’s units
Not only
inexperienced
chemistry
students can be
confused by units
Whoops!
Time waits for no one
Prefixes
Remember these: case is
important – compare M and m
Mega- (M) 1,000,000
kilo- (k) 1,000
deci- (d) 1/10
centi- (c) 1/100
milli- (m) 1/1,000
micro- () 1/1,000,000
nano – (n) 1/1,000,000,000
106
103
10-1
10-2
10-3
10-6
10-9
The seven fundamental units of
measurement
Physical property
Length
Mass
Time
Name of unit
meter
kilogram
second
Symbol
m
kg
s
Electrical current
ampere
A
Temperature
kelvin
K
Luminous intensity
candela
Cd
Amount of substance
mole
mol
Unit summary
Length: meter (m)
Length is fundamental unit. In metric system,
meter is standard unit.
Original physical standard meter is kept in
Paris. Modern definition:
“Length of path travelled by light in vacuum
during a time interval of 1/299 792 458 of a
second”
It equals 39.37 inches.
1m = 100 cm then 1 inch = 2.54 cm.
Comparisons:
centimeter - width of your fingernail
kilometer - 0.60 miles
millimeter - thickness of a dime
Mass: kilogram (kg)
Mass is fundamental unit; it measures quantity
of matter present. Although mass and weight
are used interchangeably in conversation,
mass and weight have different meanings.
Weight includes effect of gravity on mass. In a
space capsule, your weight would be zero
(absence of gravity) but your mass is same as
on earth. Standard unit of mass is kilogram
(kg).
Conversions factors:
1 pound = 454 g
2.2 pounds (lb) = 1 kilogram (kg)
1 gram (g) = 1000 milligrams (mg) or 1 mg = 0.001 g
1 kilogram (kg) = 1000 grams (g) or 1 g = 0.001 kg
Volume (two common units in S.I.)
Volume is derived unit (using length units). It
measures space. Standard unit of measurement is
meter cubed (m3) or centimeter cubed (cm3).
Note: In chemistry, standard unit of volume for liquid is
the liter (L) – not strictly S.I. The liter is similar to a
quart in the English system.
Conversion factors:
1 liter (L) = 1.06 quarts (qt)
1 quart (qt) = 0.946 liters (L)
1 liter (L) = 1000 milliliters (mL)
1 mL = 0.001 L
1 mL = 20 drops
1 mL = 1 cm3 (or 1 C.C.)
Relationship between cm3 and mL
1 L = 1 dm3; 1 dm = 10 cm, 1 dm3 = 103cm3, 1 mL = 1 cm3
Derived units
Derived units can
be resolved into
combinations of
fundamental units
Area and volume
involve only the
units of length
Most involve
combinations of
different units
Quantity
Units
Area
m2
Volume
m3
Density
kg/m3
Speed
m/s
Force
kg m/s2 (newton N)
Pressure
kg/(m s2) (pascal Pa)
Energy
kg m2/s2 (joule J)
Dimensions and relations
between units
It is important to keep track of dimensions in
derived units when making conversions:
1 cm = 10 mm
1 cm2 = 10 x 10 = 100 mm2
1 cm3 = 10 x 10 x 10 = 1,000 mm3
Conversion factors and unit
factors
Making conversions between different
units is very important
Always keep track of units in calculation
Conversion factor: 1000 mg = 1 g
Unit factors
1g
1
1000mg
1000mg
1
1g
There are two unit factors for any
conversion
Unit factors at work
How many grams are there in 2680 mg of
sucrose?
Conversion factor: 1 000 mg = 1 g
1g
Unit factor
1
1000mg
? g = amount in mg x unit factor
1g
? g  2680mg x
1000mg
Unit factor has value of 1 – no change in value
Unit factor causes old units to cancel
1g
? g  2680 x
 2.680 g
1000
Handy conversions
Working with unit conversions
Density
Mass divided by
volume
Units are:
g/cm3(solid)
g/mL (liquid)
kg/m3 or g/L(gas)
Density and temperature
In most cases,
density decreases
with temperature.
(Why is that?)
Water provides a
critical exception
to the rule