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Chapter 16: Chemistry in Today's World

Top ten chemists

The top ten chemists of all time, in date order.

Chemist Lived Accomplishments
Robert Boyle 1627-1691
  • Helped start the Royal Society.
  • Showed air followed laws.
  • Discovered phosphorus.
  • Christian.
Henry Cavendish 1731-1810
  • Discovered hydrogen.
Antoine Laurent Lavoisier 1743-1794
  • Made measurement an essential part of chemistry.
  • Stated the law of conservation of matter.
John Dalton 1766-1844
  • Atomic theory.
  • Showed methane is made of carbon and hydrogen.
  • Quaker.
Humphry Davy 1778-1829
  • Used electricity to refine elements.
  • Discovered potassium, sodium, barium, strontium, calcium, magnesium.
  • "Discovered" Michael Faraday.
Jöns Jakob Berzelius 1779-1848
  • Analysed 2,000 compounds.
  • Established the law of definite proportions*.
  • Discovered cerium, selenium, thorium.
Michael Faraday 1791-1867
  • Explained the operation of a battery.
  • Discovered benzene.
  • Christian - belief in a triune God led him to discover how electricity, magnetism and light are related (and thus was an even greater physicist than he was a chemist).
  • Believed the Bible contains perfect truth.
Louis Pasteur 1822-1895
  • Discovered optical isomers.
  • Explaned fermentation.
  • Christian.
Dmitri Ivanovich Mendaleev 1834-1907
  • Periodic table.
William Ramsey 1852-1916
  • Discovered whole family of noble gases and isolated argon, krypton, neon, xenon.
  • 1904 Nobel Prize in chemistry.
  • Christian.

* The law of definite proportions says that a particular compound will always be made of the same amount of each substance. For example, water will always be made of two hydrogen atoms and one oxygen atom - H2O. Aluminium oxide (alumina) will always be made of two aluminium atoms and three oxygen atoms - Al2O3. Because of this, knowing the molecular mass of the component atoms, we can calculate how much aluminium is in a certain amount of alumina.

Also available are the religious beliefs of some important physicists.

Distillation

Distillation is a process used to separate liquids (with different boiling points) or to purify a liquid, by boiling it then condensing it back into its liquid form. Impurities are left behind when the liquid is boiled. For example, muddy water or sea water can be distilled into pure water. Distilling sea water is a process that can be used to get drinking water from sea water.

Distillation was invented by Greek chemists in the first century AD.

Fractional distillation is used to separate a mixture of liquids when they have boiling points which are close together, normally within 25 °C. Cryongenic (very cold) fractional distillation is used when the boiling points are well below room temperature, such as with liquid air. Their vapours rise through a fractionating column and condense at different levels - the lightest ones - those with the lowest boiling point - at the highest levels. Argon is relatively inexpensive because it can be produced easily with this method.

Atmospheric Gas Proportion of Air (by volume) Boiling Point
Neon (Ne) 1 part in 65,000 -246.08 °C
Nitrogen (N2) 78.1% -195.79 °C
Argon (Ar) 0.934% -185.85 °C
Oxygen (O2) 20.95% -182.95 °C
Krypton (Kr) 1 ppm -153.22 °C
Xenon (Xe) 1 part in 20 million -108.12 °C

Carbon dioxide (0.038% of air, boiling point -78 °C) may be obtained from air distillation, however this yields only very small quantities of CO2.

Advanced - nobel gases

Why are krypton and xenon used in some lightbulbs when argon is so much more common, and therefore so much cheaper? It has to do with conducting heat from the filament. The less heat conducted from the filament, the hotter it is, and the more efficient it is. For low power bulbs a vacuum works OK, but it turns out that for high power bulbs, using an inert gas is better than using a vacuum, and some gases work better than others. From the Great Internet Light Bulb Book:

Sometimes, premium fill gases such as krypton or xenon are used. These gases have larger atoms that are better at bouncing evaporated tungsten atoms back to the filament. These gases also conduct heat less than argon. Of these two gases, xenon is better, but more expensive. Either of these gases will significantly improve the life of the bulb, or result in some improvement in efficiency, or both. Often, the cost of these gases makes it uneconomical to use them.

This all means there's no point in using neon, since argon does a better job and is cheaper.

Ethanol has a lower boiling point than water. Ethanol boils at 78.5 °C while water boils at 100 °C. However, a mixture of 95% ethanol and 5% water boils at 78.2 °C. This mixture with a lower boiling point than either component liquid, is called an azeotrope. For this reason, ethanol cannot be completely purified by direct fractional distillation of ethanol-water mixtures.