1. Units of Measurement
Section 2.2

2. Vocabulary
Measurement: dimensions, quantity, or capacity as ascertained by comparison with a standard.
Quantity: something that has magnitude, size, or amount
Example: the quantity represented by a teaspoon is volume, the teaspoon is a unit of measurement

3. Standard Measurement Nearly every measurement is a number plus a unit
There has to be an agreement on measurement standards
Mention distances in foot lengths

4. SI Measurement Le Systeme International d’Unites Adopted in 1960
Has seven base units with other units derived from these seven
Are standard measurements

5. SI Base Units found on page 34
Quantity
Unit name
Unit abbreviation
Length
meter m
Mass
kilogram kg
Time
second s
Temperature
kelvin K
Amount of substance
mole
mol
Electric current
ampere A
Light intensity
candela cd

6. SI Prefixes
These are the most commonly used prefixes (“unit” can be grams, liters, etc):
1 unit = 100 c units
1 unit = m units
1 unit = µ units
100 units = 1 h unit
1 000 units = 1 k unit
units = 1 M unit

7. Mass and Length A measure of the quantity of matter
Weight: a measure of the gravitational pull on matter
Length is frequently measured in cm or km

8. Derived SI Units (page 36)
Volume: the amount of space occupied by an object
The derived SI unit of volume is m3
cm3 is often used in chemistry
A non-SI unit of volume is the liter, L
A smaller non-SI unit of volume is the mL
1cm3 = 1mL

9. Density
Density: the ratio of mass to volume, or mass divided by volume
D = m/V
Units are expressed as kg/m3, g/L, g/mL or g/cm3 (or any other mass/volume units)

11. More about Density Density is a characteristic physical property
It is an intensive property
Can be used to help identify a substance
See the table on page 38

12. Conversion Factors
A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other
The following steps will help you use conversion factors for the rest of chemistry….they don’t ever go away!

13. Steps for Using Conversion Factors
Determine which is the smaller unit
How many of the smaller units are in one of the larger units
Set up the conversion factors as fractions
Write what you are given, then a multiplication sign, then a fraction bar
Choose a conversion factor that will make the units of the given value cancel diagonally
Solve the problem.

14. Practice Problem Convert 42.6 cm to meters.
cm is smaller, so 100 cm = 1 meter.
100 cm or ___1 m__
1 m cm
42.6 cm ● __1 m__
100 cm
This is a division problem of 42.6 divided by 100. Answer is m

15. More Practice Convert: 1.843 m to km 96.3 hg to g
Mg to mg (two step problem, go to grams first, then to mg)
4863 µL to L
1.4 x 105 g to µg