Man has always been in need of energy sources; starting with the discovery of fire. From the middle of the 17th century till the late 19th century , whale hunting was prevalent to such an extent, that certain kinds of whales, like the blue whale, the sperm whale ,were hunted for their oil till they almost became extinct. Whale oil was a necessary source of fuel and heat including whale oil for lighting, as well as for candle waxes and even in the processing of textiles and soap. An unexpected gush of oil discovery in Pennsylvania, USA, is considered the beginnings of the use of fossil fuels for Western energy sources in the 19th century. In China and Iran, seep oil as it was called, was used for fuel from early times. (4th century through 16th century)
What are fossil fuels and why do we call them that? Basically it is animal remains under great pressure and temperature over years and years that converts to crude petroleum. The distillation of petroleum leads to myriad products that literally fuels our every day life.(Distillation is a chemical process that starts with heating crude petroleum obtained from oil rigs and separated into several solids, liquids and gases used for fuel and other purposes.)
Every third week we will study organic chemistry. If you look at the Periodic Table, you find that the 6th element is carbon. Carbon is such a busy element because it can combine with other elements to form hundreds of carbon compounds. The study of these compounds has been named Organic Chemistry to distinguish it from Inorganic Chemistry, which is the study of the rest of the elements in the Periodic Table!
Today we will look at one of the combinations of carbon and hydrogen or compounds comprising hydrogen and carbon; these are called hydrocarbons. ( A compound is a chemical combination of two or more elements.) The first series of hydrocarbons have the general formula shown below and are called alkanes or paraffins.
CnH2n+2
The first alkane in the series has n=1 which makes 1 carbon atom combine with 2×1+2=4 hydrogen atoms to give :
C1H4 or CH4
as we commonly write it (when there is only one atom of any element you do not need the subscript 1 for it)
This hydrocarbon compound is named methane. Methane is also called ‘marsh gas’. As the second name suggests, it is a gas and is also highly flammable. Methane is the main component of natural gas used at homes and other places for cooking purposes:
Now let us make n= 2 and we get the second compound in the series called ethane; (n=2, so there are 2 carbon atoms and 2×2+2=6 hydrogen atoms) and the formula is C2H6 for ethane.
The next compound in the series (n=3) will be three carbon atoms combined with 2×3+2 =8 hydrogen atoms called propane
written like this/ chemical formula : C3H8
When n=4, we have 4 carbon atoms combined with 2×4+2=10 hydrogen atoms called butane and written like this/ chemical formula: C4H10
So far we have seen methane, ethane, propane and butane; all four are gases at room temperature. Notice all end in ‘ane’ and are all called alkanes.
When n=5 we have 5 carbon atoms combined with 2×5+2=12 hydrogen atoms and the name is pentane. From now on the names will be the latin word for the number so 6 carbon atoms will be called hexane and 7, heptane. 8, octane, and so on. As you notice the formula for pentane will be C5H12 , for hexane : C6H14, for heptane; C7H16 , and for octane: C8H18.
The first four alkanes were named before the nomenclature (a fancy word that means ‘naming process’)was decided.
Ethane is also used along with methane as natural gas for cooking purposes. Propane is used in propane tanks for outdoor grills. Butane is the fuel used in cigarette lighters and butane torches. Pentane is a low-boiling liquid used as a solvent and in the creation of plastic foams, hexane( liquid) is used in gasoline, and in industry as a solvent. Heptane has 0 octane rating and is not used as a fuel for gasoline since it causes high engine knock., it is used as a solvent in industry. Octane has good octane rating ( obviously) and is a major component of gasoline.
We have looked at the formula and uses of at least 8 alkanes, but it is important to picture how the arrangements of atoms or structure of these compounds looks like. Using simple materials like toothpicks and marshmallows or raisins one can construct these compounds. Here is a picture of the first three alkane compounds: methane, ethane and propane. As you can see, they are three-dimensional structures; for methane, one can see the tetrahedral structure of the compound.(The carbon atom is depicted by a tomato, and the hydrogen atom is depicted as a marshmallow here. The toothpicks are supposed to indicate the bond between the atoms; distances between the atoms, sizes of the atoms here are not accurate, but these models help understand structure.)
Next time (Week 6) we might be able to look at structure a little more closely and learn more about structural differences.Most of the alkanes studied today are the by-products in the distillation of crude petroleum. As you can see they are invaluable in our everyday life. However, next week as we look at Chemistry and Social Justice, we will talk about the problems in our society as a result of our over-dependence on petroleum/ fossil fuels.Careening from the near extinction of whales we are now at the point of near exhaustion of our fossil fuel energy resources.
Activities for middle school teachers: Let students figure out the structures of nonane, (9 carbon), decane etc till , say n=20. Students can also draw a graph using graph paper, making the number of carbon atoms on the x-axis, and the number of hydrogen atoms on the y-axis and plot a graph.(For example the x point for methane will be 1 unit and the y point will be 4 units.) What will be the shape of the plotted points? Why? Can the student now predict the structure of any alkane from that plotted graph? How will they do it?
If the language arts teacher is reading “Moby Dick” by Herman Melville, students will have an idea about the hunting of whales for whale oil two centuries back.
Nuggets of Information:The word ‘petroleum’ comes from 2 Greek words,’petra’ for rock and ‘oleum’ for oil.
Only the Inuit people have the legal rights to hunt whales today.
In 1859,workers in USA discovered petroleum jelly as a by-product in the oil rigs . They were not too happy with the sticky product, but found it was effective in the treatment of minor scratches and bruises. Today it is sold as Vaseline.
References:
http://sjvgeology.org/history/index.html
http://io9.com/5930414/1846-the-year-we-hit-peak-sperm-whale-oil
http://www.petroleum.co.uk/alkane-chemistry
http://historicaltidbits.blogspot.com/2012/05/petroleum-jelly.html
http://www.newworldencyclopedia.org/entry/Petroleum
Tags: alkanes, hydrocarbons, nomenclature, organic chemistry, petroleum, whales
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