New Metallurgy Resources

AUS-e-TUTE has just added new metallurgy resources.
Tutorials, game, test and drills on the chemistry of deciding how to extract a metal from its ore.
Visit http://www.ausetute.com.au

Paraquat

On Monday 12th November 2012, a Queensland farmer was out spraying paraquat, one of the most widely used herbicides (weedkillers) in the world. The pressure pump unit released and sprayed paraquat into the farmer's mouth. Tragically, 24 hours later the farmer died.


Because paraquat is a highly toxic chemical, it is available in Australia and the United States only to trained users and is not supplied for home or garden use. Even though it is so toxic to humans, it is still widely used because it kills a wide range of grasses and weeds very quickly and becomes biologically inactive on contact with the soil.

Paraquat is the trade-name for 1,1'-dimethyl-4,4'-bipyridinium dichloride. The structural formula is shown on the right.
1,1'-Dimethyl-4,4'-bipyridinium dichloride is a yellow solid at room temperature and pressure and smells faintly like ammonia.

 Commercially, paraquat is available as a solution at a concentration of 250 g/L. This is further diluted by the farmer before applying it to the fields.


Reference
http://www.couriermail.com.au/news/queensland/lifelong-farmer-dies-from-toxic-weedkiller/story-e6freoof-1226517724826

Further Reading 
Empirical and Molecular Formula 
Relative Molecular Mass
Concentration of Solutions (molarity)
Structural Isomers

Suggested Study Questions:

1. Give the molecular formula for paraquat.
2. Give the empirical formula for paraquat.
3. Calculate the molecular mass of paraquat.
4. Calculate the moles of paraquat present in 8 L of commercially available paraquat solution.
5. Draw the structural formula for 2 possible structural isomers of paraquat.
6. Paraquat is often sold as the chloride salt as shown in the structural formula in the article above. It can also be sold as the sulfate salt. Draw a possible structural formula for the sulfate salt form.
7. In the instructions for use, the manufacturer of paraquat stresses that only clean water, water free of clay or silt, should be used to dilute the paraquat solution. Why is it so important to use clean water?
8. Suggest some safety precautions that farmers should take when preparing and using paraquat.

New Metallurgy Resources

AUS-e-TUTE has just added new tutorials, games, tests, and drills to its metallurgy section.
The new sections include:
Metal + Water Reactions
Metal + Non-oxidizing Acid Reactions
Metal + Oxygen Gas Reactions
Activity Series (metals)

Chemistry in Eclipses

The 14th November 2012 excites students of physics and those interested in astronomy. This is the date of a total eclipse of the sun. The area of totality will pass over northern Australia, from east of Darwin in the Northern Territory to the Cape York Peninsula of Far North Queensland, turning morning into darkness. The rest of Australia will see a partial eclipse.

But why would chemists get excited about a solar eclipse?

The story begins more than 200 years ago ...

Gaps in the Solar Spectrum?

In 1802 an English Chemist, William Hyde Wollaston, was the first person to record the appearance of a number of dark lines in the emission spectrum of light from the sun.

In 1814, German physicist Joseph von Fraunhofer began measuring the wavelengths of over 570 of these lines.

Fingerprinting the Sun

Robert Gustave Kirchhoff and Robert Bunsen, developed a better prism-based spectroscope and observed that the spectral lines emitted by a gas occurred at the same wavelength as the absorption lines observed when incandescent light from Bunsen's burner shone through the same gas heated at the same temperature.

Then Kirchhoff,  proposed the laws of spectroscopy which bear his name:

1. A hot solid object produces light with a continuous spectrum
2. A hot tenuous gas produces light with spectral lines at discrete wavelengths (an emission spectrum)
3. A hot solid object surrounded by a cooler tenuous gas produces light with an almost continuous spectrum with gaps at discrete wavelengths (an absorption spectrum)

A star, like the sun, will create an absorption line spectrum because the continuous spectrum emitted by the dense, opaque gas that makes up most of the star passes through the cooler, transparent atmosphere of the star.

In 1859, Kirchhoff  demonstrated that all pure substances display their own characteristic spectrum, so it is possible to use the spectrum of elements to identify elements in a mixture, just like each person's fingerprints are unique and can be used to identify them. He proposed  that the lines in the solar spectrum are caused by the absorption of light by elements in the solar atmosphere and set out to identify the elements present in our sun.

New Element Discovered

On the 18th August 1868 there was a total solar eclipse. In India, French astronomer Pierre Janssen observed this eclipse using a spectroscope. He recorded a bright yellow line with a wavelength of 587.49 nm in the spectrum of the solar prominences. The same result was also recorded by British astronomer Norman Lockyer. This line could not be due to sodium, because although sodium produces a bright yellow line (actually more than 1), the wavelength of sodium's 'line' is about 589.3 nm. Lockyer proposed that this line was due to a new element which he called helium after the greek word 'helios' meaning 'sun'.

About 10 years later, Scottish chemist William Ramsay isolated helium on earth ...... but that's another story.

References:

http://eclipse.aaq.org.au/

http://www.csiro.au/en/Outcomes/Understanding-the-Universe/Tracking-spacecraft/History-of-total-solar-eclipses.aspx

Further Reading:

Emission Spectra 

Suggested Study Questions:

1. speed of light (m/s) = frequency (s^-1) x wavelength (m)
   If the speed of light is 3 x 10⁸ ms^-1 calculate:
• find the frequency of the 'yellow line' in sodium's spectrum
• find the frequency of the yellow line for the new element found in the solar spectrum
2.  speed of light (m/s) = frequency (s^-1) x wavelength (m)
   If the speed of light is 3 x 10⁸ ms^-1 calculate:
• wavelength of blue light with a frequency of 6.9 x 10¹⁴ s^-1
• wavelength of red light with a frequency of 4.6 x 10¹⁴ s^-1
  
3. The energy of light emitted, E, is Planck's constant,h, multiplied by the speed of light divided by the wavelength of light emitted. Write a mathematical equation to represent this.
4. Use your equation above to calculate
   • energy of the blue light in question 2 above
   • energy of the red light in question 2 above
5. Complete the following generalizations:
   • The longer the wavelength of light, the ___________ energy it has
   • The shorter the frequency of light, the _________ energy it has.
6. Compare the wavelength of the 'yellow line' in sodium's spectrum and the yellow line for the 'new element'. Which element has
   • the longest wavelength
   • the shortest frequency
   • the most energy
7. Describe the difference in the spectrum of light from the sun as seen in a spectroscope compared to the spectrum of light from a fluorescent light as seen in a spectroscope.
8. Explain the differences between the two spectrum in question 7 above.

Glow in the Dark Ice

No (chemistry) party is complete without edible "glow in the dark" ice cubes.
To make your ice cubes:

•  open up some tonic water (or a bottle of "bitter lemon")
• pour it into an ice cube mold
• place the mold in the freezer until the tonic water solidifies (freezes)

To make your ice cubes glow in the dark:

• place some ice cubes in a glass of water (or cordial or carbonated beverage)
• place the glass under a UV ("black") light (even strong fluorescent light will work but the effect is not as dramatic!) and turn off the room's lights

Results : your glass of water and ice should glow a nice blue colour.


This is an example of fluorescence, the emission of light by a substance that has absorbed electromagnetic radiation. In the case of the tonic water, there is a compound in the tonic water that absorbs light in the ultraviolet region of the electromagnetic spectrum (wavelength ~ 350 nm), and emits light in the visible region of the electromagnetic spectrum (wavelength ~ 450 nm corresponding to bright blue or cyan).

The compound in the tonic water that fluoresces is known as quinine, with the molecular formula C₂₀H₂₄N₂O₂ and the structural formula shown below:

Quinine occurs naturally in the bark of the cinchona tree which is found in the tropical Andes forests of western South America. Quinine was the first effective treatment for malaria. The first medicinal uses involved drying the bark of the cinchona tree then grinding it into a powder which was then mixed into a drink (often wine), which was then drunk. The effective medicinal ingredient of the bark, quinine, was finally isolated in 1820 by French researchers Pierre  Joseph Pelletier and Joseph Bienaime Caventou.
During World War II, the Axis Powers had control over most of the commercial quinine production centres, so the Allied Powers were cut off from their supply of quinine, a necessary war-time commodity for fighting in the tropics. Then in 1944, the American chemists R.B. Woodward and W.E. Doering succeeded in producing quinine in the laboratory.




Quinine is no longer recommended as a first-line treatment of malaria, instead another plant-derived organic compound is used, artemisinin, but that's a different story.

Further Reading:
Emission Spectroscopy
Empirical Formula
Relative Molecular Mass (molecular weight, formula mass, formula weight)
Percent Composition
Parts per Million Concentration
Functional Groups


Suggested Study Questions:

1. Draw a diagram to describe what happens when quinine absorbs UV light and emits bright blue/cyan light.
2. Imagine you were to view the light emitted by the tonic water through a spectroscope. Draw a sketch of the emission spectrum you would expect to see.
3. Use the molecular formula for quinine to find its empirical formula.
4. Calculate the relative molecular mass (molecular weight, formula mass, formula weight) of quinine.
5. Calculate the percentage of each element present in quinine.
6. Assume a 1L bottle of tonic water contains 15ppm quinine. Calculate the
   • mass of quinine contained in the bottle
   • moles of quinine in the bottle
   • quinine concentration in mol L^-1
7. Using the structural formula for quinine, identify an aliphatic double bond (that is, a double bond that does not occur in an aromatic ring), an aromatic (benzene) ring, and an hydroxyl group