Download CHEM121 Lecture Ch1 student

CHEM 121
Chapter 1
Winter 2015
Instructor: Alissa Agnello
[email protected]
1
Why study Chemistry?
2
Chemistry:
the study of matter
Matter:
Mass:
Weight:
Mass is just one way to describe matter…
3
Physical Properties of Materials
• Physical Property:
• can be measured or observed without changing the
material’s identity
• Intensive
• Extensive
• Physical Change
4
Chemical Properties of Materials
• Chemical Property:
• Demonstrated when changing the material’s
identity
• Chemical Change:
• Chemical reaction
5
3-minute review
Chemical or Physical Change?
• Cooking an egg
• Chopping wood
• Rusting
• Burning paper
• Water freezing
http://www.youtube.com/watch?v=I8aA7SjYsCA&feature=player_embedded#t=123
6
Classifications of Matter
Pure Substance:
Matter that has a fixed composition
• Element
• Compound
7
Molecules & Atoms
Atoms make up molecules
Diatomic molecules
Triatomic molecules
Polyatomic molecules
Homonuclear molecules:
Heteronuclear molecules:
8
Example: NaCl
9
Mixtures
Almost everything!
• Heterogeneous Mixture:
• One or more boundaries; not uniform
• Homogeneous Mixture:
• individual atoms, ions or molecules mixed
10
Mixtures v. Compounds
In mixtures…
1. Proportions of the components can vary
2. Individual properties of the components are
observable
3. Components can be separated by physical
means
11
3-minute review
Pure substance or mixture?
•
•
•
•
•
Salt water
Helium gas
Baking soda
Vegetable soup
Hydrogen peroxide (H2O2)
12
Elements
• Elements:
– primary substances from which all other things
are built.
– Cannot be broken down into simpler substances
13
The Scientific Method
Observations
Data (quantitative); “natural law”
Hypothesis
Experiment
Theory
14
Measurement
• Metric system (National Assembly of France, 1790)
• International System of Units (SI, 1960)
What do we measure?
Metric Units
SI Units
Length
Volume
Mass
Temperature
Time
Derived units: combinations of fundamental units
15
Equipment for Measurement
Length
Volume
Mass
Temp
Time
16
Scientific Notation
Width of human hair = 0.000008 m
Coefficient
Coefficient?
Power of Ten: 10x
Power?
Time to drive from Seattle to NYC = 91,000 s
Coefficient?
Power?
17
Conversion to a standard number
3.252 x 106
If power of ten is positive,
move decimal to RIGHT
4.56 x 10-3
If power of ten is negative,
move decimal to LEFT
18
Scientific Notation on Calculators
Look for:
EE
EXP
Note:
9.64 x 105 = 9.64 E5
Coefficient
Power of Ten
2. x 10-8 = 2.E-8
19
Measured Numbers
•
•
Numbers obtained when you measure a quantity
Estimate the final digit
1
2
3
4
5
6
1
2
3
4
5
6
20
Significant Figures
• All measured digits, including the estimated digit
2045 g
2.333 x 10-5 L
50. s
• Zeros not significant in 2 situations:
1.
2.
4500 cm
0.0063 kg
0.05202 L
21
5-minute review
• How many sig figs?
 0.00500 L
 53,069 s
 0.00004715 m
 0.509 kg
• Write the numbers above in scientific notation.
• How many sig figs does each have now?
22
Exact Numbers
• counted numbers
• definition comparing two units in same
measurement system
NOT considered as significant figures!
23
3-minute review
What is the temperature on each
(˚C) thermometer? (sig figs!)
Is each of the following an exact or measured number?
•
•
•
•
The
The
The
The
number of chair legs in this room
length of your benchtop in inches
length of your benchtop in cm
area of the projector screen
24
Sig Figs in Calculations
# of sig figs in measured numbers limits the
#of sig figs in a calculated answer.
• Multiplication and Division:
• Addition and Subtraction:
25
5-minute practice
24.64 x 3.2 =
3.525 - 5.2 =
3.525 + 6.475 =
26
Rounding Rules
Used to limit the number of sig figs?
Look at first non-significant number (to be dropped)
Is this number 4 or less?
Is this number 5 or more?
2390.321
to 4 sig figs
0.0056194 to 1 sig fig
688511 to 3 sig figs
27
Prefixes
• 590000 g or 590 kg?
• 0.0004 g or 0.4 mg?
Prefixes can be attached to units to increase
or decrease size by a factor of 10
(multiply by 10 or divide by 10)
Multiply by 10x
Multiply by 10-x
28
Common Prefixes with SI Units
Prefix
Prefix
Symbol
Word
Exponential
Notation
Mega
M
Million
1,000,000
1 x 10
6
Kilo
k
Thousand
1,000
1 x 10
3
Deci
d
Tenth
0.10
1 x 10
-1
Centi
c
Hundredth
0.01
1 x 10
-2
Milli
m
Thousandth
0.001
1 x 10
-3
Micro
μ
Millionth
0.000001
1 x 10
-6
Nano
n
Billionth
0.000000001
1 x 10
-9
Pico
p
Trillionth
0.000000000001
1 x 10
-12
Femto
f
Quadrillionth
0.000000000000001
1 x 10
-15
29
Equalities
relationships that measure the same quantity
(different units)
• Length:
• Volume:
Cubic centimeter: cc
1 cm x 1 cm x 1 cm = 1 cm3
30
Volume conversions
If 1 cubic centimeter equals 1 mL,
how many milliliters does 1 cubic meter equal?
31
Equalities used in Measurements
• Length
• Volume
• Mass:
32
Conversion Factors:
Changing Between Units
1 hr = 60 min
Conversion Factor:
1 hr
60 min
1 hr
1
1 hr
Metric Conversion Factor:
1m
100 cm
60 min
1 hr
60 min
1
60 min
100 cm
1m
33
More Conversion Factors
Metric Conversion Factors:
1 mL
1 cm 3
1 cm3
1 mL
1L
1000 mL
1000 mL
1L
Metric- U.S. System Conversion Factors:
1 kg = 2.20 lb
1 km = 0.621 mi
1 kg
2.20 lb
2.20 lb
1 kg
1 km
0.621 mi
0.621 mi
1 km
34
More Conversion Factors
• Standard equalities can be looked up in a table
• Other equalities may be stated in a problem
Examples:
• The average speed of cars driving on I-5 during rush
hour is 11 mph.
Equality:
• One five pound bag of sugar costs $4.00.
Equality:
35
Percents as Conversion Factors
• Percent means 1 per 100
Example:
• If a person is 20% body fat by mass, then:
36
Using Conversion Factors
Your patient tells you that she recently lost 15 kg.
How many pounds has she lost?
1.
What’s given?
What do we want to know?
2. What conversion factors do I need?
3. Set up problem
37
Using Conversion Factors
3. Set up problem
38
Using Conversion Factors
The recommended daily value of vitamin C is 60 mg.
If an average orange contains 45 mg of vitamin C,
how many oranges should you eat in a week?
1.
What’s given?
What do we want to know?
2. What conversion factors do I need?
39
Temperature
Measure of how hot or cold a substance is
Scale
Boiling Point H2O Freezing Point H2O
Celsius
˚C
Fahrenheit
˚F
Kelvin
K
Note: the unit is not ˚K
40
Temperature Conversions
How many units between boiling and freezing points?
Scale
Celsius
˚C
Fahrenheit
˚F
Kelvin
K
the unit 1 Kelvin equals the unit 1 degree Celsius
41
Converting Units Fahrenheit to Units Celsius
180 Fahrenheit degrees = 100 Celsius degrees
TF  1.8(TC )  32
TC

T

F
 32
1.8
o
o

42
Temperature Scale Hints
1.
2.
3.
4.
5.
43
5-minute review
Which of each of the following pairs is the higher T?
• 260 K
or
0 °C
TF  1.8(TC )  32
• -10 °C
• 260 K
or
or
o
-10 °F
250 °F
TC

T

F
 32
1.8
o

44
Density
• physical property
• intensive property
45
Density
Units:
SI: kg/m3
often use:
Density of water (at 20˚C and typical room pressure)
density of substance
specific gravity 
density of water
46
Density Table
Density can be used as a conversion factor!
(relates mass to volume)
47
Density of Solids
• How can we determine the density of a solid?
– Need to know mass
– Need to know volume
mass
density 
volume
Does this method work
for all solid materials?
48