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Intersection 8: Aqueous Chemistry
10/24/05
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Exam 2 (45 points)
• Tuesday, October 31 8-10pm CHEM 1400
• Topics: (through 10/27)
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Polarity (Lewis structures, VSEPR)
Intermolecular forces
Thermochemistry
Solutions chemistry (dilution, precipitation,
measuring concentration)
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Mole Day
6:02am-6:02 pm 10/23
Q: What element do moles love to study in chemistry?
A: Molybdenum
Q: What did Avogadro teach his students in math class?
A: Moletiplication
Q: What do you get when you have a bunch of moles
acting like idiots?
A: A bunch of Moleasses
http://www.moleday.org/
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Outline
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Finish thermochemistry
Revisiting spectroscopy
Aqueous notes/Water Project
Scientific Inquiry
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H2O(l) → H2O(g) DH >0
H2O(s) → H2O(g) DH >0
H2O(g) → H2O(l) DH <0
H2O(g) → H2O(s) DH <0
H2O(s) → H2O(l) DH >0
H2O(l) → H2O(s) DH <0
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Problem 5
Suppose that you add a small ice cube to room
temperature (25oC) water in a coffee cup
calorimeter. What is the final temperature
when all of the ice is melted? Assume that
you have 200. mL of water and that the ice
cube weighs 15.0 g and is at 0oC before
being added to the water.
Heat of fusion of water = 333 J/g
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Problem 6
If you want to convert 56.0 g ice (at 0oC) to
water at 75.0oC, how many grams of
propane (C3H8) would you have to run to
supply the energy to melt the ice and then
warm it to the final temperature?
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Silicon-Based Life
Space slugs – Star Wars
Is silicon-based life likely to be more stable or less stable
than carbon-based life?
J. Chem. Ed. 1988, 65, 414.
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Stability of Silicon vs Carbon
• Consider decomposition of alkanes and
silanes to the elements (no oxygen in space
for that slug to worry about).
• Consider combustion of silanes and alkanes
(will those silicon-based life forms make it
on earth?).
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Thermochemical Behavior with Respect
to Reversion to the Elements
Si2H6 (g) → 2 Si (s) + 3 H2 (g)
C2H6 (g) → 2 C(s) + 3 H2 (g)
DHof Si2H6 (g) = 80.4 kJ/mol
DHof C2H6 (g) -84.7 kJ/mol
DHrxn = 0 + 0 – 80.4 = -80.4 kJ/mol
Exothermic !
DHrxn = 0 + 0 – (-84.7) = 84.7 kJ/mol
Endothermic!
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Thermochemical Behavior with
Respect to Combustion
7/2 O2 (g) + Si2H6 (g) → 2 SiO2 (s) + 3 H2O (g)
DHf =
Si2H6 (g) = -80.4 kJ/mol
SiO2 (s) = -911 kJ/mol
H2O(g) = -242 kJ/mol
CO2 (g) = -394 kJ/mol
C2H6 (g) = -85 kJ/mol
DHrxn = [2(-911) + 3(-242)] – [1(-80.4)]
= -2468 kJ
Exothermic !
7/2 O2 (g) + C2H6 (g) → 2 CO2 (s) + 3 H2O (g)
DHrxn = [2(-394) + 3(-242)] –[1 (-85)]
= -1429 kJ
Exothermic!
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Silicon-Based Life
Space slugs – Star Wars
Is silicon-based life likely to be more stable or less stable
than carbon-based life?
Thermochemical considerations indicate that silicon-based
life would tend to decompose exothermically!
Our space slug unlikely to survive.
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Muskov Case Study
How did you determine if the level of nitrate
in the well was higher than the MCL?
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NO3
-
+
+ Zn + 2H
-
NH2 + NO2 + 2H
HO3S
+
sulfanilic acid
HO3S
N
N +
NO2- + Zn+2 + H2O
HO3S
(1)
N
N + 2 H2O
N
N
(2)
diazonium cation
NH2
HO3S
NH2
magenta
1-naphthylamine
4-[(4-amino-1-naphthalenyl)azo]- benzenesulfonic acid
+
+H
(3)
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Measuring Concentrations of
Contaminants
• Utilize spectroscopy if the molecule absorbs
light.
Transmittance, T = P / P0
% Transmittance, %T = 100 T
P
Po
b
sample
Absorbance,
A = log10 P0 / P
A = log10 1 / T
A = log10 100 / %T
A = 2 - log10 %T
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What kind of relationship do absorbance and concentration have?
Describe why and how you would use absorbance to find concentration?
(use an equation in your description)
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Beer-Lambert law: A=ebc
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absorbance (no units, since A = log 10 P0 / P )
e
molar absorptivity with units of L mol-1 cm-1.
Molar absorptivity is a constant unique to every
colored molecule at a particular wavelength.
b is the path length of the sample, that is, the
length that the light must travel through the
sample expressed in centimeters.
c is the concentration of the molecule in
solution, expressed in mol L-1 (M)
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Molar Absorptivity
A compound with a high molar absorptivity is
very effective at absorbing light (of the
appropriate wavelength); a very low
concentration of this compound will have a
high absorption. A compound with a low
molar absorptivity absorbs less light per
unit concentration, so it will take a higher
concentration of this compound to reach the
same absorbance.
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Path Length
The Beer-Lambert Law implies that the fraction of
the light absorbed by each layer of solution is the
same.
cm
0
0.2
0.4
0.6
0.8
1.0
Abs
0.0
0.3
0.6
0.9
1.2
1.5
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One note on case study: Antibacterial Soaps
• “Normal usage" (according to directions) of these
products will destroy some beneficial bacteria.
Fortunately, the normal bacteria population within
the septic system is sufficient and adequate to
quickly recover. Significant treatment problems,
with conservative use, should not occur. Excessive
use of these products in the home can cause
significant and even total destruction of the
bacteria population.”
• University of Arizona
http://ag.arizona.edu/pubs/water/az1258.html
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Aqueous Chemistry
Picture from: http://www.twingroves.district96.k12.il.us/Wetlands/WaterLilies/WaterLily.html
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Why is water important?
• Support life (cook, food, heat/cool,
economy)
• Clean
• Transportation
• Recreation
• More plants and animals live in water than
on land
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What are common water issues?
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Pollution/health
Ownership
Who polices it
Who cleans it up (who pays)
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Distribution of Drinking Water on Earth
Source
Volume
Percent of total water
(thousands of km3)
Oceans
1,320,000
97.3
Icecaps and Glaciers
29,200
2.14
Groundwater
8350
0.61
Freshwater lakes
125
0.009
Saline Lakes and Inland
Seas
104
0.008
Soil Moisture
67
0.005
Atmospheric water
13
0.001
Rivers
1.25
0.0001
From: Kegley, S. E., Landfear, D., Jenkins, D., Gross, B., Shomglin, K. Water Treatment:
How Can We Make our Water Safe to Drink? Norton: 2004.
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Drinkable Water
Define the desirable characteristics of drinkable
water.
Is the best water supply composed of 100% H2O?
What is the water source for our community?
How many of you have lived someplace where there
was a septic system? Where well water was used
as the drinking source?
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What’s in water that is harmful?
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Drinking Water Standards
Congress passed the Safe Drinking Water Act in
1974. Amended in 1986 and 1996, the law requires
the EPA to set standards for contaminant levels such
that the concentrations of these species do not
threaten public health and safety.
1) Primary contaminants: those substances that may cause
serious health problems above certain concentrations.
2) Secondary contaminant: substances that are not toxic but
detract from water quality, affecting such characteristics as
appearance, smell, and taste.
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EPA Standards
MCL maximum contaminant level enforceable
MCLG maximum contamination level goals
MCL (mg/L)
MCLG (mg/L)
CN- 0.2
0.2
Hg
0.002
0.002
As
0
0.10 (as of 1/23/06)
Question 1
Figure 1 represents a 1.0 L solution of sugar dissolved in
water. The dots in the magnification circle represent the
sugar molecules. In order to simplify the diagram, the
water molecules have not been shown.
12 dots
Which response represents the view after 1.0 L of water was added
(Figure 2).
6 dots
7 dots
12 dots
24 dots
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What’s added to water
intentionally?
• What may you want to be there?
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Bubbles
Caffeine
Vitamins
Soy
Sugar
Flavors
Fluoride
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Bottled Water
• According to the Beverage Marketing
Corporation, manufacturers sold more than $7.7
billion worth of bottled water in the United States
in 2002.
• The average U.S. consumer drank 21 gallons of
bottled water,
• A 1997 report published in International Journal of
Sports Nutrition found that in 52 healthy
nonsmoking adults, who exercised 30 minutes two
to four times a week, drinking flavored water
actually increased fluid consumption by 20
percent.
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Water Project
Friday 11/3
Mon 11/13, 11/20
Wed 11/29
Mon 12/11
Proposal Meeting
Lab Work Days
Poster Session Planning
Poster Session
Paper Due
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Proposal
Hypothesis: Use one to two sentences to describe a testable
scientific hypothesis that will be the focus of your miniproposal.
Significance: Use two to three sentences to say why testing
this hypothesis is significant.
Planned Experiment: Write a concise paragraph that
describes your planned experiment. This should include
details of obtaining field samples, laboratory experiments
planned, instrumental analysis planned etc.
Anticipated Results: Write several sentences describing the
likely positive and negative outcomes of your experiment.
Possible Conclusions: Write several sentences describing
the conclusions you could reach based upon the
experiments you are proposing.
Instruments and Materials Needed: List the instruments
you need to use and the materials you need.
See course website for template
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Proposals
Proposal Meetings during studio, Friday 11/3
– 12 minutes
– 1 hard copy of proposal for us to keep (in
template format)
– No more than 5 minutes to present proposal
orally
– Questions and discussion
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Other Facets of “Scientific
Research”
• Does trial and error fit into scientific
research?
• Does creativity fit into scientific research?
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Complexity: Molecules vs.
Systems vs. People
• What are the differences?
• Do you still use the scientific method?
• Do you understand the consequences of
your actions/results?
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Characteristics of Good Inquiry
• Investigations are conducted for different reasons:
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Exploring new phenomena
Checking previous results
Test how well a theory predicts
Compare different theories
• Sometimes scientists can control conditions in
order to obtain evidence. When that is not
possible for ethical reasons, they try to observe as
wide a range of natural occurrences as possible in
order to discern patterns.
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Characteristics of Good Inquiry
• There are different traditions in science
about what is investigated and how, but they
all have in common certain beliefs about the
value of evidence, logic, and good
arguments. There is agreement that
progress in all fields of science depends on
intelligence, hard work, imagination, and
even chance.
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Characteristics of Good Inquiry
• Scientists in any one research group tend to see
things alike, so even groups of scientists may have
trouble being entirely objective about their
methods and findings. For that reason, scientific
teams are expected to seek out the possible
sources of bias in the design of their investigations
and in their data analysis. Checking each other’s
results and explanations help, but there is no
guarantee against bias.
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Bias
• Symphony trials
• Unconscious bias (Reskin, B. Regional
Review, 2005, 33-37.)
– Women, minorities, elderly, overweight
http://implicit.harvard.edu/
• Bias even in scientific results…how?
• Is bias an ethical issue?
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From: http://microbiology.georgetown.edu/education/bioscipoladv.html
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Science Policy
• How does research impact decisions about
life/funding?
• Should research be published and open to
everyone?
– (milk/terrorism)
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Science Policy: Budget
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Proposed Total Federal
Budget, FY2006
Fiscal year 2006 runs from October 1, 2005 to
September 30, 2006. The Bush Administration, in its
proposed budget, did not include spending on the
wars in Iraq or Afghanistan.
Other includes general science, space and technology;
energy; agriculture; commerce and housing credit;
community and regional development; general
government; allowances; and undistributed offsetting
receipts.
Source: Office of Management and Budget, Budget of
the U.S. Government, FY2006, Historical Tables,
Table 5-1.
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National Science Foundation
(NSF)
The National Science Foundation (NSF) budget was cut in
2005
In 2006, there is a proposed increase of 2.4% to $5.6 billion
Most increase allotted to facilities funding
Most programs receive a 1% increase (but still would be
below 2004 budget)
Cuts in education and training
Total number of research grants funded in 2006: 6310
1 in 5 applications funded
From: http://www.aaas.org/spp/rd/prel06pr.htm
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Science Policy: Laws
• Environmental controls
• Speed limits
• BAC
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Arsenic
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MCL (maximum contamination limit)
1976 initial MCL set to 50 ppb
Jan 16, 2001 set to 10 ppb
Feb 2001 10 ppb merits further review;
NAS study recommends 3 ppb the limit
achieved using current treatment
technologies
• Oct 31, 2001 set to 10 ppb
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MSF