Lecture 4

 Watch Faraday's Lecture 4, The Nature of the Atmosphere

ADDED AFTER CLASS

1) Link to gas simulation: http://www.falstad.com/gas/

2) Figure: electromagnetic spectrum

3) Link: one person's interpretation of the cummings poem:

http://poetryandscience.blogspot.com/p/blog-page_28.html

4) Link: poem by Billy Collins:

https://www.poetryfoundation.org/poems/46712/introduction-to-poetry

I welcome your comments.

••••••

• Chemical Equations

    Test for carbon dioxide:

    Production of carbon dioxide from heating marble or shells (calcium carbonate):

Read or Watch

Spectroscopy, a tool for analysis of molecular structure 

A detailed record of energy absorbed by a substance (called its absorption spectrum) is like a fingerprint of that substance, and is not likely to be identical to the spectrum of any other substance. A spectrum can be compared (by a computer program) to a library of spectra of known substances, in order to identify the substance.

Even the very simple water molecule (H-O-H) can vibrate in several ways, as shown by its IR spectrum. 

Roughly speaking, each band of low transmittance results from a different way that a water molecule can vibrate, each vibration associated with a different frequency of IR absorption.

Shown below are the infrared spectra of three similar compounds, called o-, m-, and p- aminophenol. (The spectra are displaced vertically to allow comparison.)

• (March 2014 
• International Journal of Electrochemistry 2014(3):1-11)

• 
  

(source)

Although these tree compounds are very similar in structure and properties, they are easily distinguishable by their IR spectra.

••••••

• Separations and Purification: How Do Chemists Obtain Pure Samples for Study?

••••••

Chromatography

This animation shows thin-layer chromatography to separate the pigments in spinach leaves. 

Animation

(wait and watch -- be patient and it will repeat)

Chromatography of a spinach-leaf extract.

Different plant pigments travel at different

rates, revealing the number of pigments present,

as well as some other properties of 

them (e.g. their individual colors).

(Animated .gif file made at https://ezgif.com/maker)

This type of separation is called adsorption chromatography, because it takes advantage of the varying  tendencies of different pigments 1) to adsorb (hang onto the surface of) onto the white surface (powdered silica) and 2) to dissolve in the moving solvent and thus be pulled along the surface.

Another example of chromatography (called affinity chromatography) is testing for Covid-19 using a lateral-flow cartridge.

Notice that the movement of each component (antigen, antibody, ...) depends upon its affinity (tendency to combine tightly and specifically with) for other components on the strip. Some components can move freely along the strip, which others are physically bound and do not move. When a freely moving component binds to a bound one, the freely moving one stops moving.

••••••

• Read this poem

in time of daffodils( who know , e e cummings

Submit Your questions using the instructions at the bottom of this page.
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Additional Resources (optional, but recommended)

Commentary on Lecture 4
by the producers of the video series