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BiochemistryChemical Engineering
Nanotechnology
Physical Chemistry
Environmental Chemistry
Organic Chemistry
Inorganic Chemistry
CHEMISTRYCHEMISTRY
Observations
Hypothesis
Experiment
Theory
The Scientific Method
Data (quantitative); “natural law”
Measurement• Metric system (National Assembly of France, 1790)• International System of Units (SI, 1960)
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What do we measure?Length
VolumeMass
Time
Temperature
Metric Unitsm
L
g
s
˚C
SI Units
m
m3
kg
s
K
Derived units: combinations of fundamental units
Ex. Speed (m/s)
Equipment for Measurement
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Length
Volume
Mass
Time
Temp
Scientific Notation
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Coefficient
Power of Ten: 10x
Width of a human hair = 0.000008 m
Coefficient?
8 Power? 10-6
8 x 10-6 m
Seconds to drive from Seattle to NYC = 90,000 s
Coefficient?
9 Power? 104
9 x 104 s
Scientific Notation on Calculators
Your calculator should work with scientific notation! Look for:
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EE EXP
Note:9.64 x 105 = 9.65 E5
Coefficient Power of Ten
2. x 10-8 = 2.E-8
Scientific Notation
Conversion to a standard number
3.252 x 106
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If power of ten is positive, move decimal point to the
RIGHT(add zeros if necessary)
If power of ten is negative, move decimal point to the
LEFT(add zeros if necessary)
4.56 x 10-3
0.00456
3252000
Measured Numbers – Numbers obtained when you measure a quantity– Estimate the final digit
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1 2 6543
Read greater than 4 and less than 5; estimate last digit
1 2 6543
Read greater than 4.8 and less than 4.9; estimate last digit
4.84 in
4.8 in
Significant Figures
• All measured digits, including the estimated digit
4.84 cm
2045 g2.333 x 10-5 L50. s
• Zeros not significant in 2 situations:– At the beginning of a decimal number– At the end of a number without decimal point
4500 cm
0.0063 kg
0.05202 L 9
Exact Numbers
• A counted number (not measured!)– Ex. # of students in this classroom
• A definition comparing two units in same measurement system– Ex. 1 ft = 12 in– Ex. 1 kg = 1000 g
NOT considered as significant figures!
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Significant Figures in Calculations
• In lab, at work, we measure things. Then what?
• The number of sig figs in measured numbers limits the number of sig figs in a calculated answer.
You can’t have more detail in your answer than
you have in your measurements
Number of sig figs in answer depends on what type of calculations you performed
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Sig Figs in Calculations• Multiplication and Division:
– Final answer has the same number of sig figs as the measurement with the fewest significant figures
• Addition and Subtraction:– Final answer has the same number of decimal places
as the measurement with the fewest decimal places
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24.64 x 3.2 = 78.848
79.
3.525 - 5.2 = -1.675
-1.7
3.525 + 6.475 = 10
10.000
Rounding Rules
How do we limit the number of sig figs? Rounding!
Look at first non-significant number (to be dropped)
Is this number 4 or less?Is this number 5 or more?
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Round “down”Round “up”
2390.321 to 4 sig figs
2390.
0.0056194 to 1 sig fig
0.006
688511 to 3 sig figs
689000
Prefixes
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Is it easier to write:• 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
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
Equalities used in MeasurementsEquality:
A relationship between two units that measure the same quantity
• Length: 1 m = 100 cm = 1000 mm
• Volume:1 L = 10 dL = 1000 mL
1 dL = 100 mL
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Cubic centimeter: cc
1 cm x 1 cm x 1 cm = 1 cm3
Thinking about volume conversions…
If 1 cubic centimeter equals 1 mL,how many milliliters does 1 cubic meter
equal?
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100 cm x 100 cm x 100 cm = 1000000 cm3
1 m = 100 cm
1000000 cm3 = 1000000 mL
1 x 106 mL
1 x 103 L
• Mass:1 kg = 1000 g1 g = 1000 mg1 mg = 1000 μg
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Equalities used in Measurements
Conversion Factors: Changing Between Units
1 hr = 60 min
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Conversion Factor:
hr 1
hr 11
min 60
min601
Metric Conversion Factor:
min 60
hr 1
hr 1
min60
cm 100
m 1
m 1
cm 100
More Conversion Factors
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Metric Conversion Factors:
3cm 1
mL 1
mL 1
cm 1 3
Metric- U.S. System Conversion Factors:
lb 2.20
kg 1
kg 1
lb 20.2
L 1
mL 1000
mL 1000
L 1
1 kg = 2.20 lb
mi 0.621
km 1
km 1
mi 621.01 km = 0.621 mi
More Conversion Factors
• Standard equalities can be looked up in a table (Table 1.9 in your book, for example)
• Other equalities may be stated in a problem
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Examples: • The average speed of cars driving on I-5 during
rush hour is 11 mph.
Equality: 11 miles = 1 hour
h 1
mi 11
mi 11
h 1
• One five pound bag of sugar costs $4.00. Equality: 1 bag = 5 lb =
$4.00
Percents as Conversion Factors
• Percent means 1 per 100
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Example: • If a person is 20% body fat by mass, then:
body kg 100
fat kg 20
20 kg fat = 100 kg body total
fat kg 20
body kg 100
End of class Practice Questions• How many sig figs are in each the following?
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?
• Write a conversion factor relating micrograms to grams
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Practice Questions
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Is each of the following an exact or measured number?• The number of chair legs in this room• The length of your benchtop in inches• The length of your benchtop in cm• The area of the projector screen
What is the temperature on each (˚C) thermometer shown? (sig figs!)
4.9 ˚C 61.5 ˚C
Exact
Measured
Measured
Measured
Using Conversion Factors
1. What’s given? What do we want to know?
2. What conversion factors do I need?
3. Set up problem
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weight lost (kg)= 15 kg
Your patient tells you that she recently lost 15 kg.
How many pounds has she lost?
weight lost (lb)= ? lb
kg lb
2.20 lb = 1 kg lb 2.20
kg 1
kg 1
lb 20.2
factor(s) conversion Given
Using Conversion Factors
3. Set up problem
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lb 2.20
kg 1
kg 1
lb 20.2factor(s) conversion Given
15 kg x ?
kg lb
lb 2.20
kg 1 kg 15
kg 1
lb 2.20 kg 15
81818.6lb
kgkg
33kg
kglblb 33
Check sig figs!
Using Conversion Factors
1. What’s given? What do we want to know?
2. What conversion factors do I need?
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1 week
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?
# of oranges
week # oranges
days 7
week1
day 1
mg 60
orange 1
C vitamin mg 45
week 1 week1
days 7
day 1
mg 60 mg 45
orange 1oranges 33333.9
oranges 9
days mg vitamin C
Physical Properties of Materials
• Physical Property:– can be measured or perceived without
changing the material’s identity– Intensive
• Independent of amount of substance
• Ex. Boiling point
– Extensive• Depends on amount of substance
• Ex. Mass, volume
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Density
• Relationship between mass and volume
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volume
massdensity
V
m
• Density is a physical property
• Density is an intensive property 4 times more mass
4 times more volume
V4
m4
V
m
Density
• Units: – SI: kg/m3
– often use: g/L
g/mL
g/cm3
g/cc
• Density of water (at 20˚C and typical room pressure)
1 g/cc 1 g/mL
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Density of Solids
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• How can we determine the density of a solid?
– Need to know mass– Need to know volume volume
massdensity
Measure displacement
of water
Does this method work for all solid materials?
Density Table
Density can be used as a conversion factor!
(relates mass to volume) 32
Specific Gravity (sp gr)
Ratio between density of substance & density of water
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waterofdensity
sample ofdensity gravity specific
Measure sp gr with a hydrometer
Units for sp gr?
waterofdensity
sample ofdensity gr sp
mlg 1.1
mlg 1.2
Unitless!
Temperature
• Measure of how hot or cold a substance is relative to another substance
• Scales and Units
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Scale Boiling Point H2O
Freezing Point H2O
Celsius ˚C
Fahrenheit ˚F
Kelvin K
100˚C 0˚C
212˚F 32˚F
373.15 K
273.15 K
Note: the unit is not ˚K
Temperature Conversions
How many units are between boiling point and freezing point of water?
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Scale
Celsius ˚C
Fahrenheit ˚F
Kelvin K
100˚C – 0˚C212˚F –
32˚F
= 100 units= 180 units
373 K –273 K
= 100 units
the unit 1 Kelvin equals the unit 1 degree Celsius 273TT CK
Converting Units Fahrenheit to Units Celsius
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180 Fahrenheit degrees = 100 Celsius degrees
degrees Celsius 100
degrees Fahrenheit 180C 1
F 8.1o
o
C 1
TF 8.1T
oC
o
F
o32
oCF 32 )T(8.1T
Things to Remember about the Temperature Scales
1. 0 K is absolute zero2. You can never (ever ever ever) have a
temperature of negative K3. The unit for the Celsius scale is the degree C (˚C)4. The unit for the Fahrenheit scale is the degree F
(˚F)5. The units for the Kelvin scale is the Kelvin (K)
6. A change of x Kelvin = a change of x ˚C
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K 300 -K 350 C300 -C350 oo
Start value and end values are different; Both changed the same amount (50 K units = 50 ˚C
units)
Precision and Accuracy• Precision: reproducibility• Accuracy: how close to actual value
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Temp (˚C)