1. Chapter 3.2 Units of Measurement

2. Using SI Units SI = International System of Units
The standards of measurement used in science are those of the metric system
All metric units are based on multiples of 10. As a result, you can convert between units easily

3. There are six SI base units
From these base units, all other SI units of measurement can be derived
Density and pressure
SI Base Units
Quantity
SI base unit
Symbol
Length
meter m
Mass
kilogram kg
Temperature
kelvin K
Time
second s
Amount of substance
mole
mol
Volume
meter cubed m3

4. Commonly Used Metric Prefixes
Symbol
Factor
kilo k
10 3 = (1000)
hecto h
10 2 = (100)
deca D
10 1 = (10)
gram, liter, meter
g, L, m
deci d
10-1 = (1/10)
centi c
10-2 = 1/100)
milli m
10-3 = (1/1000)

5. Length The SI Unit for length is the meter (m)
For very large and very small lengths, a unit of length may have a prefix
For small distances, the prefix millimeters (mm) could be used
Prefix milli- means 1/1000, so 1 mm =0.001 m.
For large distances....kilometers (km) can be used
The prefix kilo- means 1000, so 1 km = 1000 m

6. Volume The SI unit of volume is a cubic meter (m3)
A more convenient unit of volume for everyday use is the Liter (L), a NON-SI unit
A smaller, NON-SI unit of volume is the milliliter (mL)
1 mL and 1 cm3 are the same volume
The units milliliter (mm) and cubic centimeter (cm3) are thus used interchangeably

7. Mass The SI Unit of mass is kilogram (kg)
A more convenient unit of volume for everyday use is the gram (g)
There are 1000 grams in 1 kilogram (1000g = 1kg)

8. Weight
Weight is a force that measures the pull on a given mass by gravity.
The weight of an object can change with its location
An astronaut weighs less on the moon but has the same mass

9. Density mass volume Density =
Density is the ratio of the mass of an object to its volume
The relationship between an object’s mass and its volume tells you whether it will float or sink in a given situation
mass
volume
Density =
Density is an intensive property (does not depend on the amount of matter)

10. Units of Density
The SI unit of density is kilograms per cubic meter (kg/m3)
Units of density vary depending on the units for mass and volume being measured
Increasing density (mass per unit volume)
10 g
0.53 g/cm3
19 cm3
10 cm3
3.7 cm3
0.88 cm3
1.0 g/cm3
2.7 g/cm3
11.4 g/cm3

11. Corn syrup sinks below water because it is more dense
As shown below, corn oil floats on top of water because it is less dense
Corn syrup sinks below water because it is more dense
Corn oil
Water
Corn syrup

12. Densities of Some Common Materials
Solids and Liquids
Gases
Material
Density at 20°C (g/cm3)
Density at 20°C (g/L)
Gold
19.3
Chlorine
2.95
Mercury
13.6
Carbon dioxide
1.83
Lead
11.3
Argon
1.66
Aluminum
2.70
Oxygen
1.33
Table sugar
1.59
Air
1.20
Corn syrup
1.35–1.38
Nitrogen
1.17
Water (4°C)
1.000
Neon
0.84
Corn oil
0.922
Ammonia
0.718
Ice (0°C)
0.917
Methane
0.665
Ethanol
0.789
Helium
0.166
Gasoline
0.66–0.69
Hydrogen
0.084

13. Density and Temperature Relationship
The volume of most substances increases as the temperature increases, while the mass remains the same.
Therefore, Density of a substance generally decreases as its temperature increases.
Water is an important exception (density increases as temperature increases)

14. PRACTICE PROBLEM
A copper penny has a mass of 3.1 g and a volume of cm3. What is the density of copper?

15. PRACTICE PROBLEM
A rock is determined to have a mass of 8.2 g. The rock is dropped into a graduated cylinder containing 20.0 mL of water. The volume of the cylinder rises to 31.0 mL. Determine the density of the rock?

16. PRACTICE PROBLEM
What volume would grams of Gold occupy? (Gold has a density of 19.3 g/cm3)

17. PRACTICE PROBLEM
The density of osmium, which is the densest metal, is g/cm3. What is the mass of a block of osmium that measures 1.00 cm x 4.00 cm x 2.50 cm?

18. PRACTICE TIME!