1
How?
Why?
Light Tools
Building and confirming tools for inquiry
Think with me
•
Why do you see colors when some chemicals are flamed?
•
Why do different chemicals => different colors?
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Assertion I: (proposed model): unlike planets, electrons are
only allowed discrete energies*
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Assertion II: Energies that don’t take an electron to an allowed
place are ignored by the electron, doesn’t move
*If the earth should stop revolving,
Spinning slow enough to die...
--IF, David Gates (Bread)
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Hydrogen Atom Simulator
3
(Dan Damelin)
•
http://chemsite.lsrhs.net/FlashMedia/html/flashEMR.h
tm
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Also in Further Explorations
• Predict: what happens to an arbitrary-energy photon?
• Predict: what happens to one that matches a difference
between current and potential orbital
Set ‘pause mode’ to on
4
Why are there holes in sunlight?
Assume: the light is ‘born’ as all wavelengths
http://antwrp.gsfc.nasa.gov/apod/ap070624.html
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Tool using
How are these
different?
•
Using a thermometer to test temperature
•
pointing stick at sky, say magic words, wait for rain
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using ‘pH paper’ to count ‘protons’
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using the Ba(OH)2 ‘test for’ carbon dioxide
•
counting geigs with a Geiger counter
•
believing in ‘global climate change’
Any sufficiently advanced technology is indistinguishable from
magic. --Arthur C. Clarke
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Rankings
7
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Empirical--you saw it, touched it, etc.
•
Reasoned argument from documented/identified assumptions &
previous knowledge
•
Repeatedly established by others
•
Never: assertions by authority regardless of the nature (or
volume) of that authority
Suck it & see
8
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We’ll have tubes with chalk or filter paper; drop these in the specs
•
Look at the beam (far red may be hard to see)
•
slowly and carefully move the wavelength selector
•
Look again
•
Reset spec to wavelength indicated on machine
Driving Ms. Spec
Set wavelength
Set for infinite absorbance
(blocked path)
Set zero
absorbance
Be careful when setting infinite absorbance!
Tick mark, NOT infinity symbol
9
Calibrating your eye
•
Graph paper pp. J-13 to 20
•
Predict: how will a blue liquid absorb? A green one?
•
Draw the graph (wavelength vs. absorbance)
10
To your specs!
•
On your desk is a bank of tubes
•
Find the absorbance of each at each wavelength
•
Zero machine EACH time you go to a new one! Don’t
trust those ahead of you or the machine to stay
zeroed
11
Data (one per person)
Blue
Violet
Red
Green Yellow
350
430
500
590
630
660
This should take 15’.
leaf
12
Graphing
•
Create a graph and table for HW
•
Separate graph for each color allows you to more easily
visualize the behavior of each color
•
Make a NEW table to turn in because you will need your
old table next week in class
•
See rubric!!!
•
How is a table useful? A graph?
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FYI: Dye Structures
14
Napthol Green
FDC Yellow5
Yellow
Crystal Violet
FDC Blue1
FDC Red 3
The Joy of Dilution
•
What fraction of molecules would you have to remove for
there to be 1/2 as many collisions between beam & dye?
•
OK, build a solution with 1/4 absorbance of stock (2 ways
about this)
•
•
Confirm by checking initial absorbance at a
wavelength that it will likely absorb HIGH, and final
absorbance at the same wavelength
•
Is it 1/4 the initial absorbance?
Tubes should be covered with parafilm
15
16
Photosynthesis
“Makin’ things with light*”
*Lite-Brite ad jingle
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Flight of
the
electron
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Photosynthesis:
Intro
What’s in a leaf
•
Predict: what will we find when we grind up a leaf?
•
Protocol: p. 11-3
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Graph absorption of spinach extract
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‘ultra’-violet light it (high or low energy)?
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Note!! These wavelengths re-do your DNA!!
19
20
Fashioning an
assay
Using the oxygen that plants belch out
Photosynthesis
6CO2 + 6H2O
Light
C6H12O6 + 6O2
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Deflating, inflating a leaf
•
If we deflate a leaf, what will happen if we put it in a beaker of
water?
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How can you tell if photosynthesis is happening?
•
What are the inputs of photosynthesis? The products?
•
How can you test for these?
Doing it!
23
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Cut out 5-7 leaf disks with hole punch, suction air out in syringe
(half full with buffer) until they all sink  too much and they will
die
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Buffer solution – keeps them at a happy pH
•
Set up in small beaker under the lights in 20mL of buffer, observe!
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This is practice for next week!
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Next week!
•
You’ll take the data you have from this
week to create a red-passing, bluepassing or green-passing solution
•
This will be used to test whether different
portions of the visible spectrum are
equally potent for photosynthesis
Sadava, Life, Fig. 8-6
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Semester project!
• Resume experimenting in 2 weeks
• Remember to email me if there were extra
supplies you needed by November 5!
• Reports due the week after Thanksgiving
Presentations
• Last presentations in 2 weeks
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Table & Graph of absorbance data
Dilution worksheet (pp. 11-9 & 10)
Homework