11

Light ToolsLight ToolsBuilding and confirming tools for

inquiryBuilding and confirming tools for

inquiry

How? Why?

2

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 the electron, doesn’t move

*If the earth should stop revolving, Spinning slow enough to die...--IF, David Gates (Bread)

3Hydrogen Atom Simulator

(Dan Damelin)

• http://chemsite.lsrhs.net/FlashMedia/html/flashEMR.htm

• Also in Further Explorations

Set ‘pause mode’ to on

• Predict: what happens to an arbitrary-energy photon?• Predict: what happens to one that matches a difference between current and potential orbital

4Why are there holes in sunlight?

http://antwrp.gsfc.nasa.gov/apod/ap070624.html

Assume: the light is ‘born’ as all wavelengths

55

Tool usingTool using

6How 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

7Rankings

• 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

8

Suck it & see• 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

9Driving Ms. Spec

Set for infinite absorbance(blocked path)

Set wavelength

Set zero absorbance

Be careful when setting infinite absorbance! Tick mark, NOT infinity symbol

10Calibrating 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)

11

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

12Data (one per person)

Blue Violet RedGree

nYello

wleaf

350

430

500

590

630

660

This should take 15’.

13

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?

14FYI: Dye Structures

Crystal Violet

Yellow

Napthol Green

FDC Blue1

FDC Red 3

FDC Yellow5

15The 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

1616

PhotosynthesisPhotosynthesis“Makin’ things with light*” “Makin’ things with light*”

Lite-Brite ad jingle

17

Flight of the electro

n

18

Photosynthesis: Intro

19What’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!!

2020

Fashioning an assay

Fashioning an assay

Using the oxygen that plants belch outUsing the oxygen that plants belch out

Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

21

Light

22Deflating, inflating a leaf

• If we deflate a leaf, what will happen if we put it in a beaker of water?

• How can you tell if photosynthesis is happening?

• What are the inputs of photosynthesis? The products?

• How can you test for these?

Doing it!• 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

• Buffer solution – keeps them at a happy pH

• Set up in small beaker under the lights in 20mL of buffer, observe!

• This is practice for next week!

23

24Next week!

• You’ll take the data you have from this week to create a red-passing, blue-passing 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!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

• 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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HomeworkHomework

Table & Graph of absorbance dataDilution worksheet (pp. 11-9 & 10)Table & Graph of absorbance dataDilution worksheet (pp. 11-9 & 10)