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?
•
Assertion I: (proposed model): unlike planets, electrons are
only allowed discrete energies*
•
Assertion II: Energies that don’t take an electron to an allowed
place are ignored by it
*If the earth should stop revolving,
Spinning slow enough to die...
--IF, David Gates (Bread)
2
Hydrogen Atom Simulator
(Dan Damelin)
•
http://chemsite.lsrhs.net/FlashMedia/html/flashEMR.htm
•
Also in Further Explorations (on course website)
•
Predict: what happens to an arbitrary-energy photon?
(on the slide bar labled ‘Photon Energy’ these are 10,
11, 12 & 13)
•
Predict: what happens to one that matches a difference
between current & potential orbital? ((on the slide bar
labled ‘Photon Energy’ these are 10.20, 12.09, etc.)
Set ‘pause mode’ to on
3
What is ‘color’
•Is there a difference between your
shirt and a neon light?
How does the ‘Atom Simulator’
help us understand…
6
Tool using
How are these
different?
•
Using a thermometer to test temperature
•
pointing stick at sky, say magic words, wait for rain
•
using ‘pH paper’ to count ‘protons’
•
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
7
Capturing CO2
H2O + CO2 -> H2CO3
H2CO3 -> HCO3– -> CO32–
CO32– + Ba2+ ->BaCO3 (white ppt.)
Rankings
9
•
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
Principles of
spectrophotometry
10
Driving Ms. Spec
Set wavelength
Set for infinite absorbance
(blocked path)
Set zero
absorbance
**Appendix D also reviews how to use this
Spec
11
SEE for yourself!
12
•
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 by tape on spec
13
Evaluating your expectations
•
Graph paper pp. J-13 to 20
•
Predict: how will a blue liquid absorb? A green one?
To your specs!
• Tubes in the rack
• Find the absorbance of each color at
each wavelength (record – Appendix I has
tables)
• MOVE your body to the next wavelength (the
next spec)
•Protocol for chlorophyll on 11-3
14
15
Data
Blue
Violet
Red
Green Yellow
350
430
500
590
630
660
This should take 15’.
leaf
Graphing
•
Create a graph, table for HW
•
See rubric!!!
16
FYI: Dye Structures
17
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;
confirm
•
Tubes will be covered
18
19
Photosynthesis
“…converting light energy into chemical
energy in the C-C & C-H bonds of sugar.”*
* Freeman – fourth edition
Photosynthesis
Light
6CO2 + 6H2O
C6H12O6 + 6O2
21
Photosynthesis:
Intro
22
Fashioning an
assay
Using the oxygen that plants belch out
23
Deflating, inflating a leaf
•
How can you tell if photosynthesis is happening?
•
What are the inputs? The products?
•
How can you test for these?
What’s in a leaf
•
Predict: what will we find when we grind up a leaf?
•
Protocol: p. 11-3
•
Graph absorption of spinach extract
•
‘ultra’-violet light it (high or low energy)?
•
Note!! These wavelengths re-do your DNA!!
24
Looking at a leaf, what
would you hypothesize
would be the most
effective wavelengths
for photosynthesis?
(what is your
mechanism?)
25
26
Semester project!
27
Table & Graph of absorbance data READ
the rubric CAREFULLY!
Dilution worksheet (pp. 11-9 & 10)
Homework