1. Units of Measurement

2. OBJECTIVES
Distinguish between a quantity, a unit, and a measurement standard.
Name and use SI units for length, mass, time, volume, and density.
Distinguish between mass and weight.
Perform density calculations.
Transform a statement of equality into a conversion factor.

3. KEY TERMS Quantity SI Weight Derived unti Volume Density
Conversion factor
Dimensional analysis

4. UNITS OF MEASUREMENT Chef recipe Measurements represent quantity
QUANTITY: is something has magnitude, size or amount.
Not the same as a measurement
EX:
A quantity represented by a teaspoon is volume
teaspoon  measurement
Volume quantity

5. Scientists worldwide use SI measurements
Scientists all over the world have agreed on a single measurement system called Le Systéme International d’Unités, abbreviated SI.
Adopted in 1960 by General Conference on Weights and Measures
7 base units
Most other units are derived
Non-SI units still commonly used

6. Scientists worldwide use SI measurements
SI units are defined in terms of standards of measurements.
Standards are objects or natural phenomena that are of a constant value, easy to preserve and reproduce, and particular in size.
International organizations monitor the defining process
US: National Institute of Standards and Technology (NIST)
NOT 75,000
Becuase coma in other countries is used to represent the decimal point.

7. Prefixes added to SI base units indicate larger or smaller quantities
Seven SI base units are listed in the table below.
Quantity
Quantity Symbol
Unit Name
Unit Abbreviation
Length L
Meter m
Mass M
Kilogram kg
Time t
Second s
Temperature T
Kelvin K
Amount of substance N
Mole
mol
Electric Current I
Ampere A
Luminous Intensity Iv
candela cd

8. Prefixes added to SI base units indicate larger or smaller quantities
All other SI units can be derived from these 7 fundamental units
Prefices added to the names of SI base unkits are used to represent quantities that are larger or smaller than the base units.
EX:
Prefix centi-, abreviated c, represents exponential factor 10-2, which equals 1/100
1 centimeter  1 cm = 0.01 m

9. Prefix
Unit abbreviation
Exponential factor
Meaning
Example
Tera T
1012
1 Tm = 1 x 1012 m
Giga F
109
1 Gm = 1 x 109m
Mega M
106
1 Mm = 1 x 106 m
Kilo k
103
1000
1 km = 1000 m
Hecto h
102
100
1 hm = 100 m
Deka da
101 10
1 dam = 10 m 1
1 m
Deci d
10-1
1/10
1 dm = 0.1 m
Centi c
10-2
1/100
1 cm = 0.01 m
Milli m
10-3
1/1000
1 mm = 0.001
Micro
10-6 1/
1 µm = 1 x 10-6 m
Nano n
10-9 1/
1 nm = 1 x 10-9 m
Pico p
19-12 1/
1 Pm = 1 x m
Femto f
10-15 1/
1 fm = 1 x m
atto a
10-18 1/
1am = 1 x m

10. Mass MASS: a measure of the quantity of matter
SI standard base unit for mass is kilogram
Standard of mass are used to calibrate balances all over the world
The unit of mass equal to the mass of the international prototype of the kilogram
A kilogram is 2.2 pounds
The gram, g, is 1/1000 of a kilogram
More useful for measurement of small objects
About the mass of a paper clip
Milligram, mg, used for tiny quantities
1/1000 of a gram

11. Mass vs. Weight Mass often confused with weight
Mass measure of the amount of matter
WEIGHT: a measure of the gravitational pull of matter.
Mass determined by comparing the mass of an object with a set of standard masses on two sides of the balance.
When mass on each are the same, the sides balance.
Mass does not depend on the gravity
Weight changes as gravitational forces change
Mass does not change

12. Mass vs. Weight Mass measured on instrument called a balance
Weight typically measured on a spring scale
Involves reading the amount that an object pulls down on a spring
As force of gravity increases on an object , the object´s weight increases.
Weight of an object on the Moon is about 1/6 of weight on Earth.

13. Length SI standard unit for length is the meter
1 m is about the width of an average doorway
For longer distances, a kilometer is used
1 km = 1000 m
For shorter distances, a centimeter is used
About the size of a paper clip
1 cm = 1/100 m

14. SI base units combine to form derived units
Combinations of SI base units form DERIVED UNITS.
Produced by multipying or dividing standard units
EX:
Area  length times width  m x m = m2

15. Derived SI Units Quanity Quanity Symbol Unit Unit Abbreviation
Derivation
Area A
Square meter m2
Length x width
Volume V
Cubic meter m3
length x width x height
Density D
Kilograms per cubic meter
kg/m3
Mass
volume
Molar Mass M
Kilograms per mole
kg/mol
amount of substance
Molar Volume Vm
Cubic meters per mole
m3/mol
Amount of a substance
Energy E
joule J
Force x length

16. SI base units combine to form derived units
Some combinations of units are given their own names
Pressure
kg/m·s2
Pascal, Pa
Prefixes also added to derived units
Area
cm2 or mm2

17. Volume VOLUME is the amount of space occupied by an object.
Derived SI unit of volume is cubic meters, m3.
Large unit inconvenient in chemistry lab
Cubic centimeter, cm3
1 m3 = cm3
Chemists use non-SI units for liquids and gases
Liter, L
1 L = 1000 cm3
Milliliter, mL
For smaller volume
1000 mL = 1 L
Cubic centimeter and milliliter are interchangeable

18. Density Cork lighter than lead even though same size
Liquid mercury heavier than water
Different substances contain different masses per volume
DENSITY is the ratio mass to volume, or mass divided by volume
DENSITY density = mass
volume

19. DENSITY

20. Density
SI unit for density is devied from the base units for mass and volume
kg/m3
Units are large for laboratory use
g/cm3 or g/mL
Physical property of a substance
Doesn´t depend on amount of sample
As mass increases, volume increases (proportional)
Ratio of mass to volume is constant
Helps to identify a substance

21. DENSITIES OF SOME MATERIALS
Solids
Density at 20°C (g/ml)
Liquids
Density a 20°C (g/ml)
Cork
0.24
Gasoline
0.67
Butter
0.86
Ethyl alchohol
0.791
Ice
0.92*
Kerosene
0.82
Sucrose
1.59
Turpentine
0.87
Bone
1.85
Water
0.998
Diamond
3.26
Sea water
1.025**
Copper
8.92
Milk
0.0131**
Lead
11.35
Mercury
13.6
* Measured at 0°C
** measured at 15°C

22. Sample Problem: Density
A sample of alumininum metal has a mass of 8.4 g. The volume of the sample is 3.1 cm3. Calculate the density of aluminum
ANALYZE
m = 3.4 g, v = 3.1 cm3, d =?
PLAN
Density = mass/volume
SOLVE
Density = 8.4 g/ 3.1 cm3 = 2.7 g/cm3
CHECK YOUR WORK

23. Practice Problems: Density
What is the density of a block of marble that occupies cm3 and has a mass of 853 g?
Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of cm3.
What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is g/mL?

24. Conversion Factors change one unit to another
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.
ALWAYS equals 1
Have to equivalent to each other
EX:
How many quarter are there in a dollar?

25. Conversion Factors change one unit to another
Use conversion factors to solve problems through dimensional analysis
DIMENSIONAL ANALYSIS is a mathematical technique that allows you to use units to solve problems involving measurements.
Quantity sought = quantity given x conversion factor

26. Deriving Conversion Factors
You can derive conversion factors if you know the relationship between the unit you have and the unit you want.
Deci- means “1/10”, its 1/10 of a meter
1 m = 10 dm

27. Sample Problem: Conversion Factors
Express a mass of g in mg and kg.
ANALYZE
1 g = 1000 mg, 1 kg = 1000 g
5.712 g
PLAN
SOLVE
5.712 g x (1000 mg/1 g) = 5712 mg
5.712 g x (1 kg/1000 mg) = kg
CHECK YOUR WORK

28. Practice: Conversion Factors
Express a length of m in centimeters and in kilometers.
Express a mass of mg in grams.