Transcript Chapter 1

Chapter 1
Chemistry and
Measurement
Dr. S. M. Condren
Chemistry
• What is it?
• Why do we study it?
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Physical States
• solid
– fixed volume and shape
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Physical States
• solid
– fixed volume and shape
• liquid
– fixed volume
– shape of container, horizontal top surface
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Physical States
• solid
– fixed volume and shape
• liquid
– fixed volume
– shape of container, horizontal top surface
• gas
– takes shape and volume of container
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Physical States
• solid
– fixed volume and shape
• liquid
– fixed volume
– shape of container, horizontal top surface
• gas
– takes shape and volume of container
• liquid crystal
– some characteristics of solid and some of liquid states
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Modern Chemistry:
A Brief Glimpse
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“Exploring the Nanoworld”
To order a kit (Special introductory price, $24 shipped to US
addresses) contact the Institute for Chemical Education
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Air Bags: How Do They Work?
http://whyfiles.news.wisc.edu/032air_bag/how_work.html
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Matter
• has mass
• mass vs. weight
• occupies space
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Scientific Method
• Experiment
• Results
• Hypothesis
– further experiments
– refine the hypothesis
• Theory
– experiments to test the theory
– refine the theory
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Law of Conservation of Mass
In an ordinary chemical reaction matter is
neither created nor destroyed.
The sum of the masses of the reactants equals
the sum of the masses of the products.
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Properties of Matter
Extensive Property
• depends on specific
sample under
investigation
• examples:
– mass and volume
Intensive Property
• identical in all samples
of the substance
• examples:
– color, density, melting
point, etc.
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Physical Property
• one that can be observed without changing
the substances present in the sample
• changes in physical properties of
substances
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Chemical Property
• the tendency to react and form new
substances
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Chemical Reaction
• reactants undergo chemical change to
produce products
sucrose ---> carbon + water
reactant
products
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Chemical Reaction
Reactions are indicated by:
• evolution of a gas
• change of color
• formation of a precipitate
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Law of Definite Proportions
• All samples of the same pure substance
always contain the same elements in the
same proportions by weight
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Pure Substances
Elements
Compounds
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Mixtures
Heterogeneous
• uneven texture
Homogeneous (Solution)
• sample uniform throughout
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Dr. S. M. Condren
Separation of Mixtures
• filtration
• distillation
• chromatography
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Filtration
• separate solids by
differences in melting
points
• separate solids by
differences in solubility
(fractional crystallization)
• mechanical separation such
as in Fig. 1.11 page 13.
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Distillation
• separation by differences in boiling point
(fractional distillation)
– distillate
– distillation
• fractionating column - part of apparatus where
separation occurs
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Dr. S. M. Condren
Chromatography
•
•
•
•
•
•
liquid-column
paper
thin-layer (TLC)
gas
HPLC
electrophoresis (DNA mapping)
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Column Chromatography
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Paper Chromatography of Inks
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Dr. S. M. Condren
Uncertainty in Measurements
Accuracy
closeness to true value
vs
Precision
reproducibility
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Accurate and/or Precise?
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Accurate and/or Precise?
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Significant Figures
Rules for determining which digits are significant:
• All non-zero numbers are significant
• Zeros between non-zero numbers are significant
• Zeros to the right of the non-zero number and to
the right of the decimal point are significant
• Zeros before non-zero numbers are not significant
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Significant Figures
Examples:
Railroad Track Scale
• 70,000,000 g
• + 500,000 g
7.00 x 107 g (scientific notation)
7.00 E7 g (engineering notation)
3 significant figures
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Significant Figures
Examples:
Regular Lab Balance
• 1,000 g + 0.1 g
1.0000 x 103 g
5 sig. fig.
• 400 g + 0.01 g
4.0000 x 102 g
5 sig. fig.
• 100 + 0.001 g
1.00000 x 102 g
6 sig.fig.
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Rules for Mathematics
Multiplication and Division
For multiplication and division, the number of significant
figures used in the answer is the number in the value with
the fewest significant figures.
(2075)*(14)
---------------- = 2.0 x 102
(144)
4 sig. fig.; 2 sig.fig.; 3 sig. fig. => 2 sig. fig.
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Rules for Mathematics
Addition and Subtraction
For addition and subtraction, the number of
significant figures used in the answer is
determined by the piece of data with the
fewest number decimal places.
4.371
302.5
-------306.8
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Rules for Mathematics
Addition and Subtraction
For addition and subtraction, the number of
significant figures used in the answer is
determined by the piece of data with the
fewest number decimal places.
4.371
302.5
-------306.8
Dr. S. M. Condren
Rules for Mathematics
Addition and Subtraction
For addition and subtraction, the number of significant figures
used in the answer is determined by the piece of data with
the fewest number decimal places.
4.371 (I truncate extra data)
302.5
-------306.8
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Exact Numbers
• conversion factors
• should never limit the number of significant
figures reported in answer
12 inches = 1 foot
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Round Off
• Chemistry is an inexact science
• all physical measurements have some error
• thus, there is some inexactness in the last
digit of any number
• use what ever round-off procedure you
choose
• reasonably close answers accepted
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Measurement and Units
length - meter
volume - liter
mass - gram
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Important Metric Unit Prefixes
deci -- 1/10*
centi -- 1/100*
milli -- 1/1000*
nano -- 1/1,000,000,000
kilo -- 1000*
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Liter
1 liter = 1 decimeter3
by definition
where
1 decimeter = 10 centimeters
therefore
1 liter = (10 centimeters)3
or
1 liter =1000 cm3 =1000 mL
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Millimeter
1 millimeter = 1/1000 meter
1000 millimeter = 1 meter
1000 mm = 1 m
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Nanometer
1 nanometer = 1/1,000,000,000 meter
1,000,000,000 nanometer = 1 meter
1,000,000,000 nm = 1 m
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Liter
1 liter = 1 decimeter3
1 liter = 1000 milliliters
1 L = 1000 mL
1 mL = 0.001 L
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Milligram
1 milligram = 1/1000 gram
1 mg = 0.001 g
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Kilogram
1 kilogram = 1000 gram
1 g = 0.001 kg
1 mg = 0.000001 kg
1 kg = 1,000,000 mg
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Conversion of Units
1 in = 2.54 cm
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Temperature
Scales:
• Fahrenheit
• Rankin
– absolute scale using Fahrenheit size degree
• Celsius
• Kelvin
– absolute scale using Celsius size degree
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Dr. S. M. Condren
Comparison of Temperature
Scales
Fahrenheit
Celcius
98.6
37.0
comfort temp. 68.0
20.0
bp water
212
100
mp
32
0
bp-mp
180
100
body temp.
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Temperature Relationships
C = 100/180 * (F - 32)
F = (180/100)*C + 32
K = C + 273.15
- 40o F = - 40o C
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If the temperature of the room goes from 20
degrees C to 40 degrees C, the ambient
thermal energy
– doubles
– is halved
– increases by less than 10%
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Density
• Mass per unit of volume => d =m/V
• Mass equals volume times density => m = V*d
• Volume equals mass divided by density => V = m/d
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Problem Solving by
Factor Label Method
• state question in mathematical form
• set equal to piece of data specific to the
problem
• use conversion factors to convert units of
data specific to problem to units sought in
answer
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Example
How many kilometers are there in 0.200
miles?
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Example
How many kilometers are there in 0.200
miles?
state question in mathematical form
#km
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Example
How many kilometers are there in 0.200
miles?
set equal to piece of data specific to the
problem
#km = 0.200 miles
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Example
How many kilometers are there in 0.200
miles?
use conversion factors to convert units of data
specific to problem to units sought in
answer
#km = (0.200 miles)
* (5280 ft/mile)
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Example
How many kilometers are there in 0.200
miles?
cancel units
#km = (0.200 miles)
* (5280 ft/mile)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
add another conversion factor
#km = (0.200)*(5280 ft)
*(12 in/ft)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
cancel units
#km = (0.200)*(5280 ft)
*(12 in/ft)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
#km = (0.200)*(5280)*(12 in)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
add still another conversion factor
#km = (0.200)*(5280)*(12 in)
*(2.54 cm/in)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
cancel units
#km = (0.200)*(5280)*(12 in)
*(2.54 cm/in)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
#km = (0.200)*(5280)*(12)*(2.54 cm)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
add still another conversion factor
#km = (0.200)*(5280)*(12)*(2.54 cm)
*(1 m/100 cm)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
cancel units
#km = (0.200)*(5280)*(12)*(2.54 cm)
*(1 m/100 cm)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
#km = (0.200)*(5280)*(12)*(2.54)
*(1 m/100)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
add still another conversion factor
#km = (0.200)*(5280)*(12)*(2.54)
*(1 m/100)*(1 km/1000 m)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
cancel units
#km = (0.200)*(5280)*(12)*(2.54)
*(1 m/100)*(1 km/1000 m)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
#km = (0.200)*(5280)*(12)*(2.54)
*(1/100)*(1 km/1000)
Dr. S. M. Condren
Example
How many kilometers are there in 0.200 miles?
solve mathematics
#km = (0.200)*(5280)*(12)*(2.54)
*(1/100)*(1 km/1000)
= 0.322 km
3 sig. fig.
Dr. S. M. Condren
Example
How many kilometers are there in 0.200
miles?
solve mathematics
#km = (0.200)*(5280)*(12)*(2.54)
*(1/100)*(1 km/1000)
= 0.322 km
3 sig. fig.
exact numbers
Dr. S. M. Condren